Note: Descriptions are shown in the official language in which they were submitted.
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SYNTHETIC AGGREGATES COMPRISING SEWAGE SLUDGE AND
OTHER WASTE MATERIALS AND METHODS FOR
PRODUCING SUCH AGGREGATES
Field of the Invention
[0001] Synthetic aggregates, and, more particularly, synthetic aggregates
comprising sewage sludge and silicoaluminous materials, and synthetic
aggregates
comprising combinations of low and high calcium containing silicoaluminous
materials.
Background of the Invention
[0002] Aggregates are essential ingredients of concrete, masonry, and cavity
fill insulation. Other applications for aggregates include filler aid or
horticultural
aggregate. Aggregates may be derived from natural sources with minimal
processing
or from naturally occurring materials that are heat treated. Aggregates may
also be
synthetic. Aggregates from natural sources, such as quarries, pits in ground,
and
riverbeds, for example, are generally composed of rock fraginents, gravel,
stone, and
sand, which may be crushed, washed, and sized for use, as needed. Aggregates
from
natural materials that may be used to form aggregates include clay, shale, and
slate,
wllich are pyroprocessed, causing expansion of the material. OPTIROC and LECA
are examples of cominercially available expanded clay aggregates, for example.
Syntlietic aggregates may comprise industrial byproducts, which may be waste
materials. LYTAG, for example, is a commercially available sintered aggregate
coinprising pulverized fuel ash ("PFA"), also known as fly ash. PFA is
produced
from the combustion of coal in power plants, for example.
[0003] Natural aggregates for use in construction are in very high demand.
However, aggregate resources are finite and extracting and processing these
materials
is complicated by environmental issues, legal issues, availability, urban
expansion,
and transportation costs, for example. There has also been a tremendous
increase in
waste generation by various industries that must be disposed of in an
environmentally
and legally acceptable manner. Typically, most generated waste is disposed of
in
landfills at a great expense. Due to the exhaustion of available landfill
sites, the
difficulties in acquiring new sites, the potential adverse environmental
effects, and the
cost of landfilling, disposal of waste materials has been a significant
problem for
many years.
CONFIRMATION COPY
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[0004] The processing and transformation of waste materials to produce
viable synthetic aggregates for use in concrete and in other applications
would
alleviate both waste problems and the depletion of natural aggregate
resources.
[0005] Aggregates may be lightweight or normal weight. Lightweight
aggregates ("LWAs") have a particle density of less than 2.0 g/m3 or a dry
loose bulk
density of less than 1.1 g/cm3, as defined in ASTM specification C330. Normal
weight aggregates from gravel, sand, and crushed stone, for example, generally
have
bulk specific gravities of from about 2.4 to about 2.9 (both oven-dry and
saturated-
surface-dry), and bullc densities of up to about 1.7 g/cm3. High quality LWAs
have a
strong but low density porous sintered ceramic core of uniform structural
strength and
a dense, continuous, relatively impermeable surface layer to inhibit water
absorption.
They are physically stable, durable, and enviroiunentally inert. For use in
concrete,
LWAs should have a sufficient crushing strength and resistance to
fragmentation so
that the resulting concrete has a strength of greater than 10 MPa and a dry
density in a
range of about 1.5 g/cm3 to about 2.0 g/cm3. Lower density LWAs may also be
produced. Concrete containing LWAs ("LWA concrete") may also have a density as
low as about 0.3 g/cm3.
[0006] Synthetic lightweight aggregates ("LWAs") have received great
attention due to the substantial benefits associated with their use in
structural
applications. Concrete containing LWAs ("LWA concrete") may be 20-30% lighter
than conventional concrete, but just as strong. Even when it is not as strong
as
conventional concrete, the LWA concrete may have reduced structural dead loads
enabling the use of longer spans, narrower cross-sections, and reduced
reinforcement
in structures. The lower weight of the LWA concrete facilitates handling and
reduces
transport, equipment, and manpower costs. LWA concrete may also have improved
insulating properties, freeze-thaw performance, fire resistance, and sound
reduction.
[0007] Sewage sludge, which is produced by biological wastewater treatment
plants, is a significant waste in terms of volume and heavy metal content.
Sewage
sludge comprises settled solids accumulated and subsequently separated from
the
liquid strea.in during various treathnent stages in a plant, such as primary
or secondary
settling, aerobic or anaerobic digestion or other processes. The composition
and
characteristics of the sewage sludge may also vary depending upon the
wastewater
treatment process and the sewage sludge treatment process applied. Sewage
sludge
can be raw, digested, or de-watered. Sewage sludge contains significant
amounts of
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organic materials and may also contain high concentrations of heavy metals and
pathogens. Sewage sludge has been generally disposed of by incineration to
form an
inert ash that is disposed by lagooning, landfilling, spreading on land as
fertilizer or
soil conditioning, and ocean dumping, for example. If the sewage sludge has
not been
treated prior to being spread on land or disposed of in a landfill,
mldesirable
contamination may occur.
[0008] Sewage sludge recycling and disposal presents considerable economic
and environmental problems. The presence of heavy metals and pathogens in the
waste, wliich may leach from the landfill, is a threat to adjacent ground and
water
supplies. The availability of landfill sites is also decreasing. In addition,
the presence
of large amounts of water in sewage sludge, which increases the weight of the
waste,
causes significant transportation and disposal costs.
[0009] Another significant waste produced is the ash streain generated from
inunicipal solid waste ("MSW") incineration. Althougll the disposal of MSW ash
residues to landfill occupies only one-tenth of the volume of the original
waste, their
management presents a problem due to considerable amounts of solid residues
produced, the majority of which is currently landfilled. Incinerator bottom
ash
("IBA") is the principal ash stream accounting for approximately 75 to 80% of
the
total weigllt of MSW incinerator residues and is a heterogeneous mixture of
slag,
glass, cerainics, ferrous and nonferrous metals, minerals, other non-
combustibles, and
unbumt organic matter. IBA is currently used in its raw form (without heat
treatinent)
in the construction of embankments, pavement base and road sub-base courses,
soil
stabilization, in bricks, blocks, and paving stones, and as fillers in
particular
applications. Although considered a relatively inert waste, leaching of heavy
metals
in these applications is possible.
[0010] MSW incineration also produces a particulate residue in the form of
dust suspended in the combustion gases or collected in emission control
devices,
which is called air pollution control ("APC") residue. This includes fly ash,
lime,
carbon, and residues collected at the pollution control systems. The
incinerator filter
dusts ("IFD") are an APC residue collected in baghouse filters produced at a
rate of
25-30 kg per 1000 kg of incinerated waste, while fly ash, which in some cases
includes IFD, accounts for about 10% to 15% of the total combined ash stream.
MSW incinerator fly ash ("IFA") contains high concentrations of hazardous
materials,
such as heavy metals, dioxins, sulphur compounds, and chlorine compounds, and
is
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therefore classified in most European countries as a toxic and dangerous
residue.
Therefore, it can only be disposed in special landfills, which is costly and
enviromnentally unsafe.
[0011] Significant volumes of residues are also produced by the mining of
minerals, ores, and stones. Typical mining operations include extraction,
beneficiation, blasting, crushing, washing, screening, cutting (stone), and
stockpiling.
These operations produce wastes, such as crushed material of different sizes,
powders,
mud residues, and waste water, that must be disposed. Marble and granite
rejects,
from cutting ornamental stones, for example, 'also generates large amounts of
rejected
mud that is discarded into rivers and lagoons. Granite sawinills and granite
cutting
machines also generate large amounts of powder and mud waste residues. The
term
"mining waste" is used herein to refer to the waste produced during these
operations.
Mining waste needs to be treated prior to lagoon or landfill disposal in order
to
prevent environmental contamination. Other mining wastes include limestone and
dolomite tailings, for example.
[0012] Electricity-generating power plants also produce large volumes of ash
residues in the form of a fine-grained particulate, known as pulverized fuel
ash
("PFA") and a coarse fraction, known as furnace bottom ash ("FBA"). The
heavier
ash material accounts for 20-30% of the total coal ash produced and is the
fraction
that falls through the bottom of the f-urnace. FBA is currently used in its
raw form as
aggregate in lightweight concrete, in Portland cement production and other
asphalt or
road base applications.
[0013] Other waste generated at high rates include cement kiln dusts ("CKD")
and blast furnace slag. CKD is a fine-powdery by-product of cement manufacture
operations captured in the air pollution control dust collection systems of
the
manufacturing plant. Approximately 14.2 million tons of CKD are produced
annually
in the United States, and about 64% of the total CKD generated is reused
within
cement plants. GGBS is a noninetallic product of the production and processing
of
iron in blast funlaces. It is estimated that approximately 15.5 million tons
of GGBS
are produced annually in the United States, and the majority is used in cement
production, as an aggregate or insulating material.
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Summary of the Invention
[0014] The economic burdens and environmental risks associated with waste
disposal make it advantageous to develop alternative techniques for converting
wastes
into safe, revenue-earning products. The reuse of wastes to produce building
and
construction materials such as synthetic aggregates would be an effective
option
because it provides a great potential for massive waste utilization, as well
as reducing
demand for non-renewable raw materials for material aggregates.
[0015] In accordance with an embodiment of the invention, a method for
producing an aggregate is disclosed comprising mixing sewage sludge from a
waste
water treatment facility with a non-coal combustion ash silicoaluminous waste
material. The method further comprises agglomerating the mixture to form an
agglomerate and pyroprocessing the agglomerate to forin an aggregate. The
waste
material may comprise municipal solid waste incinerator residues, waste glass,
blast
fui7iace slag, kiln dusts, and/or mining waste. The municipal solid waste
incinerator
residues may comprise air pollution control residues and/or incinerator bottom
ash.
Air pollution control residues include incinerator fly ash and/or incinerator
filter
dusts. The kiln dusts coinprise cement kiln dusts. The mining waste includes
granite
sawing residues.
[0016] In one example, the waste material comprises more calcium than the
sewage sludge. In this example, the waste material includes incinerator filter
dusts,
incinerator bottom ash, cement kiln dusts, waste glass, and/or blast furnace
slag. The
waste material may coinprise more than 9% calcium and the sewage sludge may
comprise less than 3% calcium. The resulting aggregate may comprise less than
about 10% calcium by dry weight. The method may comprise mixing from about
99% to about 60% sewage sludge by dry weight of the mixture with from about 1%
to
about 40% of the waste material by dry weight of the mixture. Preferably, the
method
coinprises mixing from about 80% to about 90% sewage sludge by dry weight of
the
mixture with froin about 10% to about 20% of the waste material.
[0017] In another example, the waste material comprises less calcium than the
sewage sh.idge. In this exainple, the waste material may comprises furnace
bottom
ash, granite sawing residues, and/or waste glass. The waste material may
comprise
less than about 10% calcium and the sewage sludge may comprise greater than
about
10% calciuin. The aggregate may comprise less than about 10% calcium. The
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inethod may comprise mixing from about 5% to about 95% sewage sludge by dry
weight of the mixture with from about 95% to about 5% of the waste material by
dry
weight of the mixture. Preferably, the method coinprises mixing from about 30%
to
about 70% sewage sludge by dry weight of the mixture with from about 70% to
about
30% of the waste material by dry weight of the mixture. More preferably, the
method
coinprises mixing from about 30% to about 50% sewage sludge by dry weight of
the
mixture with from about 70% to about 50% of the waste material by dry weight
of the
mixture.
[0018] The method may further comprise milling the waste material prior to
mixing. Preferably, the milling is wet milling. The mixture of the sewage
sludge and
the waste material is preferably milled prior to agglomerating. Preferably,
the
agglomerating comprises pelletizing. At least some of the water may be removed
from the wet milled waste material and at least some of that water may be used
during
pelletizing and/or quenching of the pyroprocessed agglomerate. The resulting
aggregates may have a diameter of from about 3 mm to about 40 inm.
[0019] The agglomerates may be coated with an inorganic powder. A plastic
binder may be mixed with the sewage sludge and waste material prior to
agglomerating. The plastic binder may compri'se clay. The clay binder may
comprise
from about 5% to about 20% by dry weight of the mixture.
[0020] Pyroprocessing of the agglomerate may take place in a rotary kiln.
The resulting aggregate may be a lightweight aggregate or a normal weight
aggregate,
for example. The agglomerate may be vitrified. Selected'properties of the
aggregate
may be controlled based, at least in part, on a proportion of the sewage
sludge to the
waste material and the pyroprocessing temperature. The selected properties may
inch.tde the density, water absorption. and/or strength of the aggregate.
[0021] In accordance with another embodiment of the invention, a method for
producing a sintered lightweight aggregate is disclosed comprising preparing a
mixture comprising sewage sludge from a waste water treatment facility and a
non-
coal coinbustion ash, silicoaluminous waste material, agglomerating the
mixture to
fonn an agglomerate, and sintering the agglomerate. The waste material may
coinprise incinerator fly ash, incinerator filter dust, incinerator bottom
ash, furnace
bottom ash, waste glass, blast furnace slag, ceinent kiln dusts, and/or
granite sawing
residues.
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[0022] In accordance with another embodiment of the invention, a sintered
lightweight aggregate is disclosed comprising sewage sludge from a waste water
treatinent facility and a non-coal combustion ash, silicoaluminous waste
material. A
mixture of the sewage sludge and the waste material is sintered at a
teinperature to
form the sintered lightweight aggregate. The waste material may comprise
incinerator
fly ash, incinerator filter dust, incinerator bottom ash, waste glass, blast
furnace slag,
cement kiln dust, and/or granite sawing residues, for example. The lightweight
sintered aggregate may comprise from about 2% calcium to about 10% calcium.
Preferably, the lightweight sintered aggregate comprises from about 3% to
about 6%
calcium. The lightweight sintered aggregate may be chemically inert.
[0023] In accordance with another embodiment of the invention, a
pyroprocessed aggregate comprises sewage sludge from a waste water treatment
facility and a non-coal combustion ash, silicoaluminous waste material. The
aggregate may be sintered or vitrified. The aggregate may be a normal weight
or
lightweight aggregate.
[0024] In accordance with another embodiment, a pyroprocessed aggregate
consists of sewage sludge. The sewage sludge may comprise less than 40%
organic
material, by weight.
[0025] In accordancewith another embodiment, a method for producing an
aggregate is disclosed coinprising mixing sewage sludge from a waste water
treatinent
facility and furnace bottom ash ("FBA") from a coal-burning facility,
agglomerating
the mixture to form an agglomerate, and pyroprocessing the agglomerate to form
an
aggregate. In accordance with another embodiment, a pyroprocessed aggregate is
disclosed comprising sewage sludge from a waste water treatment facility and
famace
bottom ash from a coal buniing facility.
[0026] In accordance with another embodiment of the invention, a method for
producing an aggregate is disclosed comprising reducing a moisture content of
sewage sludge from a wastewater treatment facility to a level to allow
agglomeration,
agglomerating the sewage sludge, and pyroprocessing the agglomerate to fonn an
aggregate.
[0027] In accordance with anotller embodiment, a method for producing an
aggregate is disclosed comprising milling at least one of clay or shale,
removing at
least some of the water in sewage sludge from a wastewater treatment facility,
and
mixing the sewage sludge with the clay or shale. The mixture is pelletized
and.the
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pellets are pyroprocessing to form an aggregate, in a rotary kiln. The mixture
of the
sewage sludge and the clay or shale may be wet milled.
[0028] In accordance with another embodiment, a process for producing
aggregates is disclosed comprising mixing sewage sludge from a waste water
treatment facility with slate, lime, limestone, dolomite, and/or gypsum. The
mixture
is agglomerated to form an agglomerate. The agglomerate is then pyroprocessed
to
form an aggregate. One or more natural materials, such as slate, lime,
limestone,
dolomite, or gypsuin, may be processed prior to being mixed with the sewage
sludge.
[0029] In accordance with another embodiment, a pyroprocessed aggregate is
disclosed comprising sewage sludge from a waste water treatment facility and
slate,
lime, limestone, dolomite, and/or gypsum.
[0030] In accordance with another embodiment, a method for producing an
aggregate is disclosed comprising mixing a first material, which may comprise
pulverized fuel ash from coal combustion, coal, clay, shale, slate, granite
sawing
residues, waste glass, and/or furnace bottom ash, with a second material,
which may
comprise incinerator fly ash, cement kiln dust, incinerator filter dust, blast
furnace
slag, limestone, gypsum, dolomite, and/or waste glass. The mixture is
agglomerated
the mixture to form an agglomerate and the agglomerate is pyroprocessed to
form an
aggregate. The first material may comprise less than about 3% by dry weight
calcium
and the second material may comprise more than about 9% calcium.
[0031] In accordance with another embodiment of the invention, a method for
producing an aggregate is disclosed comprising mixing sewage sludge from a
waste
water treatment facility and incinerator residues from a municipal solid waste
incinerator, agglomerating the mixture to form an agglomerate, and
pyroprocessing
the agglomerate to form an aggregate. The incinerator residues may comprise
incinerator bottom ash, incinerator fly ash, and/or incinerator filter dusts.
[0032] In accordance with anotlier embodiment of the invention, a method for
producing an aggregate is disclosed comprising mixing a first material, which
comprises first materials: pulverized fuel ash from coal combustion or clay,
with one
or more of the following second materials: slate, lime, limestone, dolomite,
gypsum,
blast fiirnace slag, incinerator fly ash, incinerator filter dust, or cement
kiln dust. The
inixture is agglomerated and the agglomerate are pyroprocessed to form an
aggregate.
[0033] In accordance with another embodiment, a pyroprocessed aggregate is
disclosed comprising a first material, which may be pulverized fuel ash from
coal
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combustion and/or clay, and a second material, which may be slate, lime,
limestone,
dolomite, gypsum, blast furnace slag, incinerator fly ash, incinerator filter
dust, and/or
ceinent kiln dust.
Brief Description of the Figures
[0034] Fig. 1 is a graph of density (g/cm3) versus pyroprocessing temperature
( C) for sewage sludge (Sample X) and mixtures of sewage sludge and granite
sawing
residue, in accordance with an embodiment of the invention;
[0035] Fig. 2 is a graph of density (g/cm3) versus pyroprocessing temperature
( C) for sewage sludge and mixtures of sewage sludge and cement kiln dust, in
accordance with an einbodiment of the invention;
[0036] Fig. 3 is a schematic cross-section of an example of an agglomerate
produced in accordance with processes of the invention;
[0037] Fig. 4 is a schematic cross-sectional view of an example of a sintered
aggregate, in accordance witlz embodiments of the invention;
[0038] Fig. 5 is a schematic cross-section of an example of a vitrified
aggregate, in accordance with embodiments of the invention;
[0039] Fig. 6 is an example of a method for producing aggregates, in
accordance with an embodiment of the invention;
[0040] Fig. 7 is a photograph of an example of sintered aggregates, in
accordance witll embodiments of the invention;
[0041] Fig. 8 is an example of another method for producing aggregates, in
accordance with another embodiment of the invention;
[0042] Fig. 9 is a graph of density (g/cm3) versus pyroprocessing
temperature ( C) for IBA and mixtures of sewage sludge and waste glass, in
accordance with an embodiment of the invention;
[0043] Fig. 10 is a graph of density (g/cm) versus pyroprocessing
teinperature ( C) for sewage sludge (Sample Y) and mixtures of sewage sludge
and
granite sawing residues, in accordance with an embodiment of the invention;
[0044] Fig. 11 is a graph of density (g/cm3) versus pyroprocessing
temperature( C) for sewage sludge and mixtures of sewage sludge and bentonite,
in
accordance with an embodiment of the invention;
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[0045] Fig. 12 is a graph of density (g/cm) versus pyroprocessing
temperature( C) for sewage sludge and mixtures of sewage sludge and limestone,
in
accordance with an embodiment of the invention;
[0046] Fig. 13 is a graph of density (g/cm3) versus pyroprocessing
temperature( C) for sewage sludge and mixtures of sewage sludge and
incinerator fly
ash, in accordance with an embodiment of the invention; and
[0047] Fig. 14 is a graph of density (g/cin3) versus pyroprocessing
teinperature( C) for sewage sludge and mixtures of sewage sludge and ground
granulated blast furnace slag, in accordance with an embodiment of the
invention.
Detailed Description of the Preferred Embodiments
[0048] The behavior of a material when heated is primarily dependent on its
composition, grain size, and mineral composition. In order to obtain a
controlled
densification with pyroprocessing temperature during production of sintered
and
vitrified products having desired densities, water absorptions, etc., a good
ratio
between fluxing materials and refractory minerals is required. Refractory
minerals,
such as silica and alumina, generally have high melting points. The presence
of
fluxing minerals, such as the alkaline earth metals calcium and magnesium, and
the
alkaline metals sodium and potassium, present in a material form of oxides,
carbonates, or sulfates, lowers the melting point of silica and alumina and
other
refractory minerals in the material. If there is a high fraction of fluxing
minerals in a
material, there is a correspondingly lower fraction of the glass network-
forming
element silicon. The fluxing minerals promote sintering and melting at the
temperature of the lowest eutectic point of the components in the mixture. In
addition, the fluxing minerals, wliich have low viscosity and high mobility,
assist in
the formation of a sintered or vitrified product, depending on the
temperatures
involved, by liquid phase sintering.
[0049] Sewage sludge is a heterogeneous waste material whose composition is
quite variable, depending principally on the characteristics of the wastewater
influent
entering a particular wastewater treatment plant and the treatinent processes
used for
wastewater and sludge treatment processes. Sewage sludge is used in certain
embodiments of the invention as the initial raw material for the production of
pyroprocessed aggregates. Sewage sludge from two different treatment plants
has
been subjected to aggregate production processing in accordance with
embodiments
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of the invention. Sewage sludge samples from one waste water treatment
facility
(Sample X, discussed in Example 1, below), comprised, in part, about 16.02%
silica
(Si02), 6.83% alumina (A1203), and 20.28% calcium oxide (CaO). Sample Y, also
discussed in Example 1, below, comprised, in part, about 31.24% silica (Si02),
6.22%
alumina (A1203), and 12.12% calcium oxide (CaO). These samples contained high
amounts of the alkali earth metals calcium, which lower the melting point of
the
remaining compounds in the sludge. Densification therefore occurs at lower
temperatures than the melting points of the refractory minerals silica and
alumina. In
addition, the calcium components act as fluxes, assisting in the formation of
a sintered
or vitrified product by liquid phase sintering. Whether a mixture is sintered
or
vitrified depends on the pyroprocessing temperature and the composition of the
mixture. The fluxing minerals melt to form a low viscosity, high mobility
liquid that
absorbs and dissolves the remaining refractory minerals very rapidly.
Furthermore,
the mobility of the silicate melt is increased by the presence of volatile
components in
the sludge. This liquid formation is responsible for an accelerated
densification
behavior of this type of sewage sludge witll increasing pyroprocessing
temperature.
[0050] Sewage sludge samples from a second wastewater treatment facility
had low concentrations of these fluxes. Sample Z, discussed below in Example
4, is
an example of a low calcium sewage sludge having a partial coinposition of
3.20%
calciuin oxide (CaO), 3.80% aluminum oxide (A1203), and 39.50% silicon oxide
(Si02). Densification took place at higher temperatures and over a wider
temperature
range, due to the higher concentrations of refractory minerals, such as
silica.
[0051] In accordance with an embodiment of the invention, a pyroprocessed
aggregate coinprising 100% sewage sludge and a method for producing such an
aggregate are disclosed. It has been found that better control of aggregate
production
may be attained by mixing the sewage sludge with an additive to modify the
composition of the sewage sludge and alter its behavior during pyroprocessing.
In
accordance with other embodiments, certain waste and natural additive
materials are
therefore mixed with sewage sludge. The selection of the additional material
depends
on the composition of the sewage sludge. Preferably, the material is chosen so
that
the resulting aggregate has a calcium content of from about 2% to about 10%.
More
preferably, the calcium content is from about 2% to about 6%.
[0052] In one example of an embodiment, sewage sludge having a high
calcium content, such as a calcium content higher than 10%, for example, is
mixed
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with low calcium silicoaluminous materials ("LCSAMs") having a calcium content
less than that of the sewage sludge, in order to modify the composition of the
sewage
sludge and, therefore, its densification behaviour during pyroprocessing. The
high
calcium content silicoaluminous sewage sludge may have a calcium content
greater
than 10% and the LCSAM may have a calcium content of less than about 10%, for
example. The LCSAMs are also referred to in this embodiment as Group A
additives
or materials. LCSAMs include waste materials, such as waste glass ("WG"),
furnace
bottom ash ("FBA"), and certain mining wastes, such as granite sawing residues
("GSR"). LCSAMs also include the natural material slate.
[0053] The addition of LCSAMs to high calciuin sewage sludge has been
found to 1) delay the densification of the material, and/or 2) increase the
temperature
range between the initial softening, sintering, and melting of the aggregates,
by
providing a lower mobility and higher viscosity melt from the LCSAMs. This has
been found to provide better control of the aggregate production process as
compared
to the processing of the 100% high calcium sewage sludge.
[0054] In anotller example of embodiment, sewage sludge having a low
calcium content is mixed with higll calcium silicoaluminous materials
("HCSAMs"),
wl-iich are referred to in this embodiment as Group B additives or materials.
Low
calcium sewage sludge may have a calcium content of less than 3% and HCSAMs
may have a calcium content of greater than 9%. HCSAMs in this embodiment
include, for example: 1) the wastes: municipal solid waste ("MSW") residues,
cement kiln dust ("CKD"), and blast furnace slag; and 2) the natural
materials:
limestone, gypsum, and dolomite. Municipal solid waste ("MSW") residues
include
air pollution control residues and incinerator bottom ash ("IBA"). Air
pollution
control residues include incinerator fly ash and incinerator filter dust.
[00551 The addition of HCSAMs to low calcium sewage sludge has been
fou.nd to 1) reduce the temperature range over which the aggregates containing
sewage sludge can be pyroprocessed; 2) provide a liquid melt that accelerates
sintering and/or vitrification; and 3) enable production of aggregates with
selected
characteristics (such as density, for exainple), dependent upon temperature
and
composition.
[0056] Waste glass comprises considerable amounts of fluxing components,
such as calcium and sodium (9% and 12% by weight, respectively), and
refractory
minerals, such as silica (71.7% by weight). Waste glass may therefore be both
a
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Group A and a Group B additive, depending on the composition of the sewage
sludge.
In other words, the waste glass can lower the calcium content of high calcium
sewage
sludge or raise the calcium content of low calcium sewage sludge.
[0057] In another example of an embodiment, synthetic aggregates from
mixes of at least one LCSAM with at least one HCSAM, are produced. In one
exainple, the LCSAMs coinprise less than 3% calcium while the HCSAMs comprise
of more than 10% calcium. It has been found that the mixtures of the LCSAMs
and
the HCSAMs provide a good ratio between refractory and fluxing minerals,
enabling
controlled pyroprocessing. LCSAMs in this embodiment include, for example, the
wastes: pulverized fuel ash from a coal burning facility ("PFA"), and the
other
LCSAMs discussed above, as well as clay, shale, and slate. The clay may be
bentonite and/or kaolin, for exainple. The HCSAMs.in this embodiment are the
same
as those discussed above, except that MSW incinerator bottom ash is not
included.
The addition of HCSAMs to LCSAMs aims to .provide a mixture with the desirable
composition of the appropriate proportion of the fluxing to the refractory
minerals, in
order to achieve a better control of the production process to manufacture
aggregates
of the desired properties.
[0058] In anotl7er embodiment, by controlling the proportions of the sewage
sludge to the second material/additive and the pyroprocessing temperature, a
range of
densities, porosities, and water absorptions of the synthetic aggregates can
be
obtained.
[0059] Fig. 1 is a graph of density (g/cin3) versus sintering temperature ( C)
for aggregates comprising sewage sludge (sample X in Example 2, below) and
aggregates comprising mixtures of sewage sludge and granite sawing residues,
over a
range of about 920 C to about 1,150 C. Curve A, corresponding to aggregates
coinprising 100% SS, shows that as temperature increases from about 920 C to
about
960 C, density increases from a low of about 1.2 g/cm3 to a maximum density of
about 2.5 g/cm3. As temperature increases from 960 C to 980 C, density
decreases
from the maximum density of about 2.5 g/cm3 to 1.7 g/cm3. Aggregates with
densities of 2.0 g/cin3 and below are referred to as lightweight aggregates
while
aggregates with densities above 2.0 g/cm3 are referred to as normal weight
aggregates.
[0060] Density increases with temperature from 920 C to 960 C because as
the product sinters, the fluxing agents in the sewage sludge melt to form a
liquid
phase that fills pores between particles in the sewage sludge by capillary
action.
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Density increases as pores are filled and the volume of the sample decreases.
In
addition, smaller particles in the liquid phase diff-use toward the larger
particles. The
melted materials form a rigid, glassy, ainorphous skeleton or matrix upon
hardening.
As the processing temperature increases, more of the compounds in the sewage
sludge
melt, substantially eliminating all the pores and forming a more glassy,
crystalline
solid matrix. At the temperature of maximum densification, essentially all of
the
pores are filled and the product is vitrified.
[0061] Density rapidly decreases with temperature from 960 C to 980 C
because further temperature increases result in sample melting and bloating.
Bloating
is caused by the entrapment of gases in the melted liquid phase, resulting
from
volatization of certain components of the sample. The entrapped gases form
pores.
[0062] As shown in Fig. 1, sewage sludge sinters rapidly over a very narrow
temperature range. For example, in order to produce a sintered liglltweight
aggregate
comprising 100% sewage sludge having a density in a range of about 1.4 g/cm3
to
about 1.8 g/cm3, the sintering temperature must be within a range of 930-940
C,
which is only 10 C wide. In addition, variations in the coinposition of a
given sample
of sewage sludge cause significant variations in the behavior of the sewage
sludge
sample during heating. The relationship between temperature and density for
different sewage sludge samples may therefore vary widely. Consequently, it is
very
difficult to achieve a sewage sludge end product having desired
characteristics of
density, porosity, water absorption, etc. The inability to control the
densification
behavior of sewage sludge having similar composition to this sample (high
calcium)
with temperature would be a significant obstacle in the production of
aggregates of
required properties in large-scale production.
[0063] The low calcium silicoaluminous materials (LCSAMs) used in
embodiments of the invention comprise more silica and less calciuin than
sewage
sludge. As described above, the sewage sludge sample (Sample X) used in
Exainples 1 and 2, below, comprised about 16.02% silica (Si02), 6.83% alumina
(A1203), and 20.28% calcium oxide (CaO). The natural LCSAM clays (bentonite
and
kaolin, for exainple), shale, and slate comprise from about 48% to 58% silica
(Si02),
from about 18% to about 29% aluminum (A1203), and less than about 3% calcium
oxide (CaO). Granite sawing residues ("GSR"), which is an example of a mining
waste that may be used in certain embodiments of the invention, comprise about
65%
silica (Si02), about 15% alumina (A1203), and about 2.6% calcium oxide (CaO).
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Waste glass comprises about 72% silica (Si02), about 2% alumina (A1203), aind
about
9% calciuin oxide (CaO). Waste glass also comprises about 12% sodium oxide
(Na20), which is also a fluxing compound, so it may be used either to increase
or
decrease the amount of fluxing agents in sewage sludge. Furnace bottom ash
("FBA"), which has the same composition as pulverized fuel ash from coal
combustion ("PFA"), comprises about 52% silica (Si02), about 26% alumina
(A1203),
and about 2% calcium oxide (CaO). The additional components of these LCSAMs
are given in the Examples, below.
[0064] As shown in Fig. 1, in an 60%/40% sewage sludge ("SS")/granite
sawing waste ("GSR") mix, for example, in order to produce a sintered
lightweight
aggregate having a density of from about 1.5 g/cm3 to about 1.8 g/cm3, the
sintering
temperature may be within a ran.ge of about 30 (from about 1,010 C to about
1,040 C). In a 40%/60% SS/GSR mix, similar densities may be achieved at a
temperature within a 65 C range of from about 1,010 C to about 1,075 C. In
addition, increasing the GSR concentration to 60% delays sintering as the
maximum
density is reached at about 1,110 C (in contrast to 960 C for 100% SS and
1,060 C
for 60%/40% SS/GSR). It is expected that further increases in GSR to 80% and
above would result in lightweight aggregates having densities of from about
1.5 g/cm3
to about 1.8 g/cm3 over a wider temperature range than the 40%/60% SS/GSR mix.
The broader temperature ranges facilitate production of aggregates of desired
density
and other properties, despite variations in composition of the SS. Fig. 1 is
based on
the results of Example 2, below.
[0065] Fig. 2 is a graph of density (g/cin) versus sintering temperature ( C)
for aggregates comprising sewage sludge (Sample Z in Exainple 4, below) and
aggregates comprising mixtures of sewage sludge and cement kiln dust, over a
range
of about 980 C to about 1,110 C. Curve B, corresponding to 100% sewage sludge,
shows that as temperature increases from about 980 C to about 1060 C, density
increases from a low of about 1.9 g/cm3 to a maximum density of about 2.4
g/cm3. As
teinperature increases from 1060 C to 1110 C, density decreases from the
maximum
density of 2.4 g/cm3 to 2.0 g/cm3. The aggregates having densities above 2.0
g/cm3
are nonnal weight aggregates.
[0066] As shown in Fig. 2, sewage sludge exhibits a delayed densification and
a broad teinperature interval between the initial material softening,
sintering and
melting, due to the high amounts of refractory components in the sewage
sludge. In
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this example, the temperatures investigated produced normal weight aggregates
having densities between 2.0 g/cm3 and 2.4 g/cm3 over a wide temperature range
of
110 C (1000-1110 C). In order to accelerate the densification behavior of the
material to produce both lightweight and normal weiglit aggregates within a
teinperature range providing predictability and production control, a high
calcium
silicoaluminous, Group B material ("HCSAM") is added to the sewage sludge. In
this
exainple, the HCSAM is cement kiln dust ("CKD"). Since CKD comprises a
significant amount of CaO (63% by weight), only a small amount of CICD is
needed
to have an accelerating effect. An addition of 5% CKD in the sewage sludge
results
in the production of lightweight aggregates having densities of from about 1.7
g/cm3
to about 2.4 g/cm3, when pyroprocessed in the salne temperature range of the
100%
sewage sludge mixture. An addition of 10% CKD in the sewage sludge results in
the
production of lightweight aggregates having densities as low as 1.4 g/cm3 and
normal
weiglzt aggregates having densities of up to about 2.4 g/cm3, between the
pyroprocessing temperatures of 940 C to 1060 C. Further additions of CKD are
not
preferred because it may further accelerate the densification of the mixture,
which
may be an obstacle in controlling the production process in a predictable
manner in
large scale aggregate production.
[0067] In a method in accordance with an embodiment of the invention, an
aggregate is formed by mixing predetermined amounts of sewage sludge and a
second
material, which may be an LCSAM or a HCSAM, depending on the composition of
the sewage sludge, agglomerating the mixture, and pyroprocessing the
agglomerate at
a selected teinperature. As discussed above, the LCSAM has less calcium-
containing
coinponents than the original sewage sludge, while the HCSAM has more calcium
than the sewage sludge. The temperature may be selected based, at least in
part, on
the proportion of sewage sludge to the silicoaluminous material ("SAM"), and
the
desired density and other properties of the aggregate, such as water
absorption and/or
strength, based on data such as that graphically represented in Figs. 1 and 2.
A
teinperature that will cause sintering is preferred. The mixture is preferably
agglomerated prior to sintering, to create agglomerates having a desired size
and
shape to foim the sintered aggregate. Pelletization is a preferred
agglomeration
inethod. The sewage sludge may be dried prior to mixing with the second
material.
Alternatively, the sewage sludge may be added in wet form having the desirable
moisture content to allow agglomeration.
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[0068] Fig. 3 is an example of an agglomerate 10 comprising LCSAM
particles 12, such as clay, shale, slate, granite sawing residue, waste glass,
and furnace
bottom ash, or HCSAM particles 12, such as cement kiln dust, blast furnace
slag,
limestone, gypsum and dolomite, and sewage sludge particles 14. Pores 16 are
also
shown. The agglomerate 10 may be pyroprocessed, for example sintered, to form
an
aggregate in accordance with an embodiment of the present invention. During
pyroprocessing, fluxing compounds, such as calcium, sodium, potassium, and
inagnesiuin oxide, and other compounds with melting points below the
processing
temperature in the original grain particles of sewage sludge 14 and high or
low
silicoaluininous materials ("SAM") particles 12, melt and flow into the pores
16. If
the SAM particles 12 are waste glass, which is a non-crystalline solid,
densification
occurs by fusing of softened glass particles by viscous sintering at
temperatures that
are generally much lower than the melting temperatures of other, crystalline
SAM
particles.
[0069] Fig. 4 is a schematic cross-sectional view of an example of an
aggregate 20 resulting from sintering the agglomerate 10, in accordance with
an
embodiment of the invention. The aggregate 20 coinprises a mixture of sewage
sludge and SAM. The agglomerate is sintered at a temperature that depends on
the
proportion of sewage sludge to SAM and the desired density and/or other
characteristics. The sintered aggregate 20 comprises a plurality of grains 22
bonded
to each otlier through a partly glassy and partly crystallized matrix 24,
resulting from
the melting and/or the crystallization of the components. The grains 22 may
comprise
silica, alumina, and other minerals with melting points above the processing
temperature. The grains 22 fully or partially crystallize during sintering,
providing an
additional bond between the grains 22. The aggregate 20 preferably has a
dense,
continuous, relatively impermeable surface layer 26, resulting from coating of
the
agglomerates 10 with an inorganic material, as discussed further below.
Internal
pores 28, which may be channel-like, and small surface pores 28a, which may be
microscopic, are also present. The surface pores may connect with the internal
pores,
enabling the aggregate 20 to absorb water. The degree of water absorption is
indicative of the voluine and connectivity of the pores.
[0070] Fig. 5 is a schematic cross-sectional view of an example of a vitrified
aggregate 30, in accordance with another embodiment of the invention. The
vitrified
aggregate 30 comprises fewer grains 22 and a larger matrix 24 than the
sintered
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aggregate of Fig. 4. Vitrification results from pyroprocessing of the
agglomerate 10
at or above the temperature of maximum densification for the particular
proportions
of sewage sludge to SAM, where most of the components of the agglomerate melt.
[0071] Highly porous lightweight aggregates, having densities as low as about
1.2 g/cm3 and water absorptions above about 40%, with very low strengths, as
well as
very strong, well-sintered lightweight aggregates with densities up to 2.0
g/cm3, lnay
be made in accordance with einbodiments of the invention. Normal weight
aggregates, with densities greater than about 2.0 g/cm3, and up to about 2.6
g/cm3, and
water absorptions close to zero, may also be made in accordance with
embodiments of
the invention. Aggregate production with sewage sludge and SAMs, and among
certain SAMs, present an advantageous reuse application.
[0072] Fig. 6 is an example of a method 100 of manufacturing aggregates in
accordance with an embodiment of the invention. The sewage sludge is first
dried, in
Step 105. Sludge may be dried in an oven at 110 C for 24 hours, for example.
If the
water content of the raw sludge is very higli, the excess water is reinoved by
filtering,
gravity settling, flocculation, or precipitation, for example, before being
dried in the
oven. Luinps of dried sewage sludge are typically formed. The size of the
lumps may
then need to be reduced. A fine powder suitable for subsequent processing is
preferably produced by dry milling or grinding, or by using a pestle and
mortar, for
example, in Step 110. In large-scale production, the dry solid cake may be
ground to
a powder by a hainmer mill, for example. The ground sewage sludge powder is
separated to remove large particles through a sieve, for example, in Step 115.
Coarse
particles, such as stones, roclcs, or metals present in the sewage sludge are
preferably
removed for further processing, as well. Separation may take place by
mechanically
shaking the sewage sludge powder onto ASTM standard stainless steel mesh
screens
having openings of 150 microns or 80 microns, for example. The sewage sludge
having particle sizes less than 150 microns is further processed.
[0073] Powders with fine particle size distributions (less than about 710
microns) have advantageous characteristics because the high surface area to
volume
ratio increases diffusion of small particles through the liquid phase to the
larger
particles, and because the powders are better distributed throughout the
aggregate,
with good packing densities.
[0074] Sewage sludge may also be used in its raw wet form, as long as the
material has suitable moisture content to be directly mixed with the SAM,
allowing
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further processing according to Steps 125-150 of Fig. 6, for example. Excess
water
content may again be removed by drying, filtering, and/or other processes, to
reach a
suitable moisture content before mixing with the additives. In this case,
Steps 105-
120 are not provided.
[0075] The ground sewage sludge powder from Step 120 is then mixed with
the appropriate SAM in the form of powder having a fine particle distribution,
in
Step 125. Mixing may be batch or continuous. If the SAM has a coarse particle
size
distribution, it may be pre-ground in a hammermill or a ball mill, for
example, using
dry or wet milling techniques, before being added to the mixer with the sludge
powder. Any amount of high or low calcium SAM may be added to the low or high
calciuin sewage sludge, respectively, for improved pyroprocessing performance.
The
preferred ranges of sewage sludge to SAM depend on whether the sewage sludge
is
high or low calcium sewage sludge. In accordance witlz an embodiment of the
invention, clay, such as bentonite and kaolin, and/or shale are wet milled in
Step 125.
[0076] Preferably, from about 5% to about 95% high calcium sewage sludge
by dry weigh.t of the mixture ("BDWM") is mixed with from about 95% to about
5%
LCSAM, BDWM. More preferably, from about 30% to about 70% high calcium
sewage sludge BDWM is mixed with from about 70% to about 30% of the LCSAM,
BDWM. In this range, the resulting aggregate has a calcuum content by dry
weight,
of from about 6% to about 15%. More preferably, from about 30% to about 50%
high
calcium sewage sludge BDWM is mixed with from about 70% to about 50% of the
LCSAM, BDWM. In this range, the resulting aggregate has a calcium content by
dry
weight, of from about 6% to about 10%. It has been found that the
densification
behavior of the mixture may be better controlled, enabling the production of
aggregates with desired characteristics, when the calcium content of the
aggregate is
from about 2% to about 10%, and even better control may be obtained when the
calcium content is from about 3% to about 6%.
[0077] Preferably, from about 99% to about 70% low calcium sewage sludge
BDWM is mixed with from about 1% to about 30% HCSAM, BDWM. More
preferably, from about 80% to about 90% low calcium sewage sludge BDWM is
mixed with from about 20% to about 10% HCSAM, BDWM. These ranges provide
aggregate calcium content similar to that discussed above.
[0078] A plastic binder, such as clay, may be added to enhance the physical
bonding of individual particles with water during granulation, which is
described in
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Step 125. The term "plastic binder" refers to a binder material having a high
plasticity index. A plasticity index of at least 10 is preferred. The clay
binder may
comprise from about 5% to about 20% by dry weight of the mixture of IBA, the
SAM, and the clay binder. The amount of binder used may depend on the type and
characteristics of the sewage sludge and the SAM, such as the plasticity of
individual
components in the mix.
[0079] After thoroughly mixing the powders, water is added to form a suitable
consistency for agglomeration, in Step 130. The mixture preferably has a clay-
like
mixture, for example. The amount of water to be added is related to the amount
and
type of additive in the mixture. For example, if the proportion of sewage
sludge to
clay is about 80% sewage sludge ("SS") to 20% clay, the amount of water
required
has been found to be about 25% by weight of the total dry weight of the
SS/clay
mixture. If the proportion is 60%/40%, then the amount of water required has
been
found to be about 28% by weight. If the proportion is 20%/80%, then the amount
of
water required has been found to be about 32%. If sewage sludge is used in its
wet
form, and the mixture of SS/SAM and optionally clay have a suitable moisture
content that allows further processing, no water needs to be added to the
mixture.
[0080] The resulting mixture is agglomerated, in Step 135. Agglomeration is
a particle size enlargement technique in wllich small, fine particles, such as
dusts or
powders, are gathered into larger masses, such as pellets. Preferably, the
mixture is
agglomerated by pelletization, wherein fine particles dispersed in either gas
or liquid
are enlarged by tu.inbling, without other external coinpacting forces. A
pelletizing
rotating drum or disc may be used, for example. The strength of the resulting
pellets
depends on the properties of the particles, the amount of moisture in the
medium, and
mechanical process parameters, such as the speed of rotation and angle of tilt
of the
rotating drunl, as is known in the art. An example of the use of a rotating
drum is
described in the examples, below. The resulting pellets are nearly spherical
or
slightly angular, and vary in color from light to darlc brown, depending on
the carbon
and iron content in the mixes. They may range in size from about 3 mm to about
40 inm, for example. As discussed above, Fig. 3 is an example of a pellet 10.
Extrusion may be used instead of pelletization. Extrusion results in a brick-
like
material that can be crushed into smaller particles after hardening.
Alternatively,
compaction may be used to produce cylindrical agglomerates, such as tablets or
other
shapes.
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[0081] The agglomerated mixture is optionally surface coated and then dried,
in Step 140. The amount of inorganic material used may be small. The pellets
may
be coated with an inorganic material that will not melt at the sintering
temperature.
The pellets may be coated by sprinkling the dust on them or by rolling the
pellets in
the dust. The use of a coating material depends on the characteristics of the
sewage
sludge and the selected additive. If the sewage sludge is high calcium sewage
sludge,
the inorganic material may comprise a LCSAM from Group A, such as granite
sawing
residues or furnace bottom ash in the form of dust, clay, ground shale, and
slate, could
also be used, for example. If the sewage sludge is low calciuin sewage sludge,
the
inorganic material may comprise an HCSAM from Group B, such as ceinent kiln
dust, incinerator fly ash, incinerator filter dust, limestone, gypsum, and
ground
granulated blast furnace slag, for exainple.
[0082] Covering the pellet surface with a thin layer of non-sticking material
results in formation of a skin on the pellet surface that decreases clustering
of the
pellets, enhances the pellet strength, and creates a thin dense outer skin on
the
aggregate, as shown in Fig. 4, for example. If a clay binder is added to the
mixture,
coating of the pellet surface is not needed to enhance pellet integrity or to
form a
coating, since the clay provides improved internal bonding. Coating is an
option,
however. Drying may talee place at about 110 C in an oven, for example. Drying
is
preferably provided because pyroprocessing wet pellets in a kiln may result in
cracking and exploding of the pellets due to rapid temperature changes.
[0083] The coated and dried pellets are pyroprocessed, in Step 145. The
pyroprocessing takes place at a temperature of from about 1000 C to about 1350
C,
for example, depending on the composition of the mixture and the desired
properties
of the aggregate, as discussed in more detail, below. The pyroprocessing may
be
sintering, which takes place at temperatures below the temperature of maximum
densification, or vitrification, which takes place at the temperature of the
maximum
densification and above. The pyroprocessing preferably takes place in a rotary
kiln.
Sintering results in increased strength and density of formerly loosely bound
particles,
through the fonnation of interparticle bonds. Vitrification results in
increased
strength at the teinperature of maximtun densification. As vitrification
progresses at
liiglier teinperatures, however, density and strength decrease due to bloating
of the
glassy ainorphous matrix, as discussed above.
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[0084] The pyroprocessed aggregate may be quenched in water, in Step 150.
Quenching cools the pellets, stopping the melting. If quenched, the resulting
aggregate 20 will have a more ainorphous matrix 24 than when air cooled, which
allows recrystallization. It is known in the art that quenching improves the
hardness,
toughness, and wear resistance of the pyroprocessed aggregates. The water may
be at
room temperature (about 30 C), for example.
[0085] After pyroprocessing and quenching, if provided, the pellets may be
crushed and graded to the desired aggregate size, in Step 155. Preferably, the
coarse
aggregates range from about 4.75 to about 19 mm. Smaller aggregates may also
be
used as fine aggregates in concrete, for exainple.
[0086] Due to pellet shrinkage during pyroprocessing, if the pellets ranged in
size from about 3 mm to about 40 mm, the pyroprocessed aggregates may range in
size from about 2 nun to about 30 min, for example. Appropriate size ranges
for the
graded aggregates may be about 4 mm to about 8 mm, which may be used in
filtration
applications, and about 12 mm to about 19 imn, which may be used in concrete.
Smaller aggregates (down to about 2 mm) may also be used as fine aggregates in
concrete, for exainple.
[0087] It is believed that as a result of pyroprocessing in accordance with
embodiments of the invention, the aggregates are chemically inert against most
substances under normal enviroiunental conditions.
[0088] Fig. 7 is an example of plurality of sintered aggregates made in
accordance with embodiments of the invention, from mixes containing 80%/20% of
SS/bentonite pyroprocessed at 990 C.
[0089] Fig. 8 is an example of a method 200 of manufacturing aggregates in
accordance with an einbodiment of the invention, in which specific SAMs having
coarse particle distributions, are wet milled before mixing with the sewage
sludge.
Additives used in the present invention that have such distributions include
IBA,
FBA, and waste glass.
[0090] IBA is added to a barrel of a ball mill in Step 205 and is milled with
water, in Step 210. Milling is used to reduce the particle size distribution
of the IBA
to a distribution that is fine, to improve pyroprocessing. Powders with fine
particle
size distributions have advantageous characteristics because the high surface
area to
volume ratio increases diffusion of small particles througll the liquid phase
to the
larger particles and because the powders are better distributed throughout the
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aggregate, with good packing densities. The resulting particles preferably
have a
mean particle size of about 45 microns and less, for example. Wet milling is
preferred because it has been found to provide more uniform particle size
distribution.
Iil addition, the liquids used in the wet milling process tend to brealc up
agglomerates
and reduce welding of powder particles. Alternatively, the IBA may be dry
milled in
a haminer mill, for example. While the metliod 200 of Fig. 8 will be described
with
respect to the use of IBA, it is understood that if FBA or waste glass are
used, they are
preferably milled, as well.
[0091] The IBA may be wet milled in a closed cylindrical container, for
example, wherein grinding spherical media such as wet mill balls, in a liquid
medium,
such as water or alcohol, apply sufficient force to break particles suspended
in the
medium. Motion may be imparted to wet ball mills by tumbling, vibration,
planetary
rotation, and/or agitation. The most important variables controlling the
powder
particle size distribution is the speed of milling (rpm), the milling time,
the amount of
grinding media, the initial particle size of the raw material, and the desired
product
size. For most efficient results, the inill should be at least half filled
with grinding
media. The milling media may be high density, aluininum spheres, for example,
with
a total weight of about four times that of the solids. Small grinding media
are
recommended for optimmn milling. When aluminum or steel balls are used,
preferred
sizes range between 1/Z and % inch. About twice as much liquid as solids is
preferably
provided. Milling may take place for about 8 hours, for example.
[0092] The wet milled IBA is separated to remove large particles through a
sieve, for example, in Step 215. If the particles are too big, they will not
fonn
homogenous pellets. Separation may take place in multiple steps. For example,
the
IBA may be mechanically shalcen over ASTM standard stainless steel mesh
screens
having openings of 355 microns or 150 microns, for example. The IBA having
particle sizes less than 150 microns is fiirtlier processed. The greater than
150 micron
fraction may be separated into different types of materials that may be reused
as a
SAM additive, as waste glass.
[0093] The resulting milled slurry of the finer fraction from Step 220 is
dewatered in Step 225. Preferably, all the free water is removed. The water
removed
is referred to as effluent, which may be used in Step 265, as discussed
further below.
Water may be removed in a filter press or other filtration apparatus, for
example.
Dewatering results in formation of a solid moist cake residue, in Step 230.
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[0094] The calce is dried and ground in Step 235. This step converts the cake
into a powder. The cake may be dried in an oven at 110 C, for example. The
powder
may be ground by a mortar and pestle, for example. In large-scale production
the dry
solid calce may be ground to a powder in a mixer with blades or a dry hammer
mill,
for example, so that the dry milled IBA solid cake may be simultaneously
ground to
powder and consistently mixed with the raw additives which are also in the
fonn of a
powder.
[0095] Before mixing the milled IBA, with the sewage sludge, the sludge is
dried, in Step 240. Sludge may be dried in an oven at 110 C for 24 hours, for
example. The solid cake produced is ground into a powder, in Step 245. The
powder
may be produced by dry milling or grinding, or by using a pestle and mortar,
for
example. The sludge powder is passed through 150 micron or 80 micron sieves to
remove coarse particles, in Step 250. The less than 150 micron fraction of
Step 255 is
thoroughly mixed with the milled IBA powder in, Step 260. Water is added to
the
mixture before the wet clay-lilce mixture is pelletized, in Step 265. The
water may be
some or all of the effluent produced from the dewatering Step 225, discussed
above.
Steps 265-285 correspond to Steps 130-155 in Fig. 6. Alternatively, sewage
sludge
may be mixed in its wet form with the IBA. However, the appropriate moisture
content is required to avoid furtlier addition of water for granulation of the
mixture.
hi this case, Steps 240-255 are not preferred.
[0096] Alternative processing may be used when the sewage sludge with the
IBA are wet milled together in a ball mill, to produce a slurry. Then the
milled slurry
is sieved through a series of sieves and dewatered in a filtration apparatus
to form a
clay-like solid cake. The solid calce is then dried at 110 C and ground to a
fine
powder, which is furtlier pelletized in the presence of water and
pyroprocessed to
forin aggregates. The milled slurry formed from wet milling both materials may
also
be dewatered to the required moisture content to allow direct pelletization of
the
mixture. Formed pellets are dried at about 110 C before entering the
pyroprocessing
stage in the lciln.
[0097] The following experiments have been performed:
EXAMPLE 1
[0098] In this example, synthetic aggregates were produced comprising
sewage sludge ("SS") and waste glass ("WG"). The average chemical compositions
(inajor oxides) of the three different SS samples used in this example are
given in
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Table A, below. Table B, below, shows the minor and trace constituents present
in
the three samples. Sample X and Sample Y were obtained from the same facility
about six months apart, while Sample Z was obtained from a second facility.
The
calcium oxide content of Sample X is 20.28% by weight; the calcium oxide
content of
Sample Y is 12.12% by weigllt; and the calcium oxide content of Sample Z is
3.20%
by weiglit. Samples X and Y are considered to be high calcium SS and Sample Z
is
low calcium SS. The average chemical coinposition of WG used is also shown in
Table A. The WG was made from soda-lime glass, which accounts for about 90% of
the glass produced in the United States. It consists mainly of silicon dioxide
(71.7%
by weight), sodium oxide (12.1% by weight), and calcium oxide (9.4% by weight)
with other minor components, such as aluminum and magnesium oxides. The
composition of the glass causes the material to densify by liquid phase
sintering at
lower temperatures than other glasses currently used to produce cerainics,
therefore
reducing energy production costs. Depending on the composition of the SS, WG
can
be used as both a LCSAM to increase the densification temperature range and
also as
a HCSAM that will act as a fluxing agent to accelerate densification. For
example,
WG may be used with sewage sludge samples X, Y, and Z to produce synthetic
aggregates.
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TABLE A: CHEMICAL ANALYSIS OF SS AND WG
Constituent Weight (%)
SS (Sample X) SS (Sample Y) SS (Sample Z) Waste glass
Si02 16.02 31.24 39.50 71.7
A1203 6.83 6.22 3.80 2.1
Fe203 2.35 6.33 6.70 0.3
CaO 20.28 12.12 3.20 9.4
Mg0 3.00 2.25 - 2.8
Na20 0.30 0.58 0.69 12.1
K20 0.59 0.32 0.28 0.9
Ti02 0.38 0.41 0.47 0.1
P205 3.90 2.64 2.43 2.43
SO3 1.85 2.11 2.87 2.87
TABLE B: MINOR AND TRACE CONSTITUENTS IN SEWAGE SLUDGE
Constituent mg/kg
Sample X Sample Y Sample Z
As 30 20 20
Ba 400 300 300
C1 940 1200 1300
Cr 700 900 900
Cu 300 200 300
Mn 90 100 100
Ni 100 100 100
Pb 200 300 300
Rb 20 20 20
Sr 300 100 100
y 10 100 10
Zn 1200 2300 3400
Zr 100 90 100
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[0099] SS sample X and WG were subjected to processing described below.
In this example, WG was added to dried SS powder before pelletization.
[00100] Sample X was oven dried at 110 C for 24 hours. The resulting dry
cake was added to a ball mill for grinding to powder. The mill was a Pascal
Engineering Co., Ltd., Model No. 21589, containing about 2.172 kg of 3/4 inch
(19.05 mm), high density, alumina sphere grinding media. The ground powder was
sieved through a 150 microns sieve to remove coarse particles.
[00101] The WG used was derived in part from bottles and window glass
separated from raw IBA. This WG was washed and oven-dried overnight at 110 C.
The WG was t11en crushed in a jaw crusher and separated to reduce the particle
sizes
to between 2 mm to 6 mm and then ground in a tungsten carbide Tema mill,
available
from Gy-Ro, Glen Creston Ltd., Brownfields, England by the use of vibrating
rings,
so that ninety five percent of the volume (d95) had a particle size less 710
microns. It
was again dry milled in a carbide mill for an additional 4 minutes to further
reduce the
particle size distribution. This fine WG fraction was used in this Example.
The d50
value of the particle size of the crushed WG was 197.6 microns, which was
reduced to
19.8 microns after 4 minutes of dry milling. In addition, WG from the wet
milled
slurry of I]BA, separated by a 710 micron sieve, was also used. This fraction
was also
ground in the Tema dry mill for 4 minutes and was combined with the first
fraction.
[00102] The ground WG was added to the sludge powder in selected
proportions of 100%/0%, 40%/60%, 60%/40% and 0%/100% (SS/WG). The ground
powder mixes of SS and WG were mixed with water (up to about 40% by total dry
weight of the resulting mixture) in a batch mixer and then fed to a rotary
drum
pelletizer having a 40 cm diameter and a 1 meter length rotating at about 17
rpm at an
angle of 30 to the horizontal. The resulting "green" pellets were generally
spherical
or slightly angular. They had an average of from about 4 mm to about 9.5 mm in
diaineter. The pellets less than 4 mm were returned to the drum for
pelletizing again.
The pellets greater than 9.5 min were broken down into smaller pellets by hand
and
also returned to the pelletizer.
[00103] The pellets were coated with PFA from coal combustion by sprinlcling
PFA powder onto tllem. The pellets were then dried at about 110 C and fed to a
rotary kiln having a 77 inm intenial diameter by 1,500 mm length, in which the
heated
zone was 900 mm long. The kiln was set to run at temperatures between 920 C
and
1,220 C for the different SS/WG mixes. The pellets traveled and rotated along
a tube
111nr.n11Z vQ nnr ,.,
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of the rotary kiln at a speed of about 2.8 rpm for about 10 minutes to about
12 minutes. In this example, the kiln was an electric fired rotary furnace
available
from Carbolite Hope Valley, England, Model No. GTF R195. The pyroprocessed
pellets were discharged from the kiln and were allowed to cool at room
temperature.
[00104] It is noted that the temperature versus density curves (such as that
shown in Fig. 1) may vary in each kiln. For example, the curves corresponding
to
particular proportions of SS and WG or other SAMs may have a temperature of
maximum densification slightly lower or higher than those using the specific
kiln
identified above. The curve shifting may be attributed to a number of factors
related
to the operational efficiency of the particular kih1, such as the stability of
the
temperature profile, energy losses, etc. It may therefore be necessary to
prepare
several samples in a particular kiln being used to identify the temperature
range over
which aggregates will have desired characteristics.
RESULTS
[00105] Tables C-D, below, summarize the physical and mechanical properties
of aggregates formed in this Example. It is noted that the aggregates showed
substantial changes in their properties with increasing concentrations of WG
in the
ss.
[00106] Table C, below, summarizes test results for aggregates comprising
different proportions of SS and WG, pyroprocessed in different temperatures
(10
centigrade degree increments). The data is an average of 4 values for the 100%
sewage sludge and an average of 2 values for all WG containing samples. The
data is
plotted on the graph of Fig. 9. The relative dry density of pyroprocessed
aggregates
was calculated using Archimedes' method and the water absorption was
determined
from the increase in weight of "surface dry" sainples after being submerged
for 24
hours.
[00107] As discussed above, increasing the amount of WG in the mixes
resulted in a broader temperature interval between the initial softening,
maximum
densification, and complete or near complete melting of the samples, due to
the
modification of the chemical composition and mineralogy of the sewage sludge
with
increasing ainounts of WG. It was also observed that maximum densification
occtu-red at higher teinperatures with increasing WG, due to the increased
concentrations of silica present in the resulting mixture. For example, 100%
Saniple X SS, has a maximum densification temperature of about 960 C. A mix of
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Sample X SS and WG in the proportion of 60%SS/40%WG, has a maximum
densification temperature of 1,030 C, and a proportion of 40%SS/60%WG has a
maximuin densification temperature of 1,060 C.
[00108] However, it has been found that the incorporation of WG in SS is not
as effective in broadening the temperature range over which pellets sinter, as
the
incorporation of other LCSAMs. For example, while 100% SS sinters to form a
lightweight aggregate of about 1.4 g/cin3 to about 1.8 g/cm3 over a
temperature range
of from about 930 C to about 940 C (10 centigrade degrees), a 60% SS/40%WG
sinters over a temperature of about 970 C to about 1,000 C (30 to about 35
centigrade
degrees) to form an aggregate in that density range. This temperature range is
similar
to that of 40% SS/60%WG pellets for the same aggregate density ranges. It is
believed that this is due to the presence of high concentrations of sodium and
calcium
oxides present in the WG, which act as fluxes. It is also believed that the
fluxes and
the melting glass produce a low viscosity melt, producing a denser, lower
porosity
product than with the otlier low calcium silicoaluminous materials.
TABLE C: PHYSICAL PROPERTIES OF SS/WG AGGREGATES
Ratio (SS/WG) Temperature Density Water
Sample X ( C) (g/cm) Absorption (%)
100/0 920 1.18 44.56
930 1.44 36.84
940 1.82 22.34
950 2.19 3.41
960 2.48 1.50
970 1.96 0.42
980 1.70 0.15
60/40 970 1.46 28.54
980 1.50 26.32
990 1.62 18.42
1000 1.71 13.21
1010 1.92 7.44
1020 2.28 0.94
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Ratio (SS/WG) Temperature Density Water
Sample X ( C) (g/cm3) Absorption (%)
1030 2.55 0.26
1040 2.11 0.10
1050 1.99 0.04
1060 1.89 0.02
1070 1.82 0.01
1080 1.71 0.01
1090 1.58 0.01
40/60 1000 1.44 21.45
1010 1.59 16.23
1020 1.75 11.84
1030 1.94 3.01
1040 2.18 1.83
1050 2.31 0.86
1060 2.62 0.42
1070 2.28 0.14
1080 2.11 0.05
1090 1.95 0.03
1100 1.75 0.01
0/100 1080 1.52 18.36
1100 1.68 13.98
1120 1.74 9.85
1130 1.88 2.56
1140 1.99 1.84
1150 2.10 0.88
1160 2.22 0.56
1180 2.48 0.08
1200 2.66 0.03
1210 2.18 0.02
1220 2.08 0.04
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[00109] As is apparent from Fig. 9 and Table C, temperature may be used to
deternnine the density and other characteristics of the sintered product, for
a given
coinbination of SS and WG. For exainple, in a 40%/60% mix of SS/WG, sintering
at
1000 C will yield a LWA with a density of about 1.4 g/cm3, while sintering the
same
mixture at 1060 C will yield a normal weight aggregate with a density of about
2.6 g/cm3.
[00110] Table C also shows the effect of WG addition on the water absorption
of the different aggregates. LWAs, which are produced at lower temperatures
than
the temperature of maximum densification, typically have some porosity. As
maximum densification is approached, the size and number of the pores
gradually
decrease to zero, as the pores are filled with melted material. Aggregates
containing
high amounts of SS exhibit a rapid reduction in water absorption capacities
with
temperature, while high WG aggregates show a more gradual water absorption
reduction with temperature. The 100% WG aggregates have substantially less
water
absorption than all other mixes at all teinperatures examined, due to the
melted glass
filling the pores produced by volatization.
[00111] Table D, below, summarizes Aggregate Crushing Values ("ACVs"), as
a percentage, for selected mixes of SS and WG, at specific pyroprocessing
temperatures. The ACVs are provided at three different temperatures for the
different
proportions of WG to SS. ACV is inversely proportional to aggregate strength.
The
selected temperatures were those causing different product characteristics and
different microstructures, for comparison. At the lower temperatures in each
set, a
sintered LWA was produced in accordance with a preferred embodiment of the
invention. At the middle temperatures, a well-sintered or vitrified, normal
weight
aggregate with small amounts of residual pores was produced, in accordance
with an
embodiment of the invention. At the higher temperatures, a vitrified LWA was
produced, also in accordance with an embodiment of the invention.
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TABLE D: AGGREGATE CRUSHING VALUE (%)
Ratio Temper. ACV Temper. ACV Temper. ACV
SS/WG ( C) (%) ( C) (%) ( C) (%)
100/0 930 57.3 960 9.8 970 13.6
60/40 970 36.4 1030 9.3 1060 14.5
40/60 1000 22.2 1060 8.9 1100 13.9
0/100 1120 15.7 1200 5.9 1220 11.2
[00112] ACVs were lower and the strengths of the aggregates were higller at
the temperature of maximum densification (middle temperature). Below that
temperature, the densities were lower, the ACVs were higher, and the strengths
of
individual or bulk aggregates were lower. Above that temperature (middle), the
ACVs started to increase as the density and aggregate strength decreased, due
to
increasing sainple melting. The aggregate strengths show the same trend of
aggregate
densities with increasing temperature, increasing to a maximum value and then
decreasing, as expected. The LWAs comprising 40% SS and 60% WG at the
temperatures shown in Table D in accordance with embodiments of the invention,
also have lower ACVs and higher strengths than the commercially available
liglltweight aggregate LYTAG, which has an ACV of about 34%, as noted below.
[00113] Based on the effect of pyroprocessing temperature and WG addition on
the properties of the pyroprocessed aggregates, shown in Fig. 9, and Tables C
and D,
a 40% SS/60% WG mix, sintered at a temperature range of 1000 C to 1100 C,
which
resulted in aggregates having densities from about 1.4 g/cm3 to about 2.6
g/cm3, is
preferred. Such aggregates may be used in a range of applications, including
as
normal weight and LWAs in concrete. This combination will sinter to form
aggregates over the broadest temperature range of 100 centigrade degrees. The
behavior of this mixture during sintering and other pyroprocessing, and the
final
properties of the resulting aggregates may therefore be more easily controlled
than in
an aggregate coinprising 100% SS. The reduced water absorption of aggregates
of
this coinbination is due to the melted glass.
[00114] Table E sunzmarizes certain physical properties (relative dry
densities
and water absorptions from Table C, and bull-, densities) and mechanical
properties
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(ACV from Table D) of aggregates from 40% SS/60% WG mix at three selected
temperatures. The corresponding properties of the commercial aggregates LYTAG
(sintered PFA) and OPTIROC (expanded clay) are also given in Table E. The
individual aggregate properties are average values of 20 measurements and the
bullc
aggregate properties are averages of 2 measurements.
TABLE E: PHYSICAL AND MECHANICAL PROPERTIES OF
AGGREGATES
Ratio SS/WG Temp. Relative Water Bulk ACV
( C) Dry Density Absorption Density (%)
(g/cm3) (%) (g/cm)
1000 1.44 21.45 0.72 22.2
40/60 1060 2.62 0.42 1.78 8.9
1100 1.75 0.01 1.03 13.9
Lytag 1.48 15.5 0.85 34.2
Optiroc 0.68 11.0 0.39 92.3
[00115] A comparison of the properties of LYTAG and the aggregates
comprising 40%/60% mix of SS/WG sintered at 1000 C, shows that the WG-
containing aggregates had comparable individual and bulk aggregate densities,
higher
water absorption, and significantly lower ACVs than that of LYTAG, showing
that
they can resist higller stresses as a bulk when loaded in compression. OPTIROC
has
very low density, relatively low water absorption, and very low strength. This
is to be
expected since OPTIROC has a honeycoinbed microstructure having a high volume
of isolated spherical porosity.
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EXAMPLE 2
[00116] In this example, synthetic aggregates were made comprising high
calcium SS Samples X and Y and granite sawing residues ("GSR"), which is a
Group B, LCSAM (2.61% calcium oxide (CaO)). The average chemical
compositions of the SS samples and the GSR used in these experiments are shown
in
Table F, below. The saine equipment used in Example 1 was used here.
TABLE F: CHEMICAL ANALYSIS OF SS AND GSR
Constituent Weight (%)
SS (Sample X) SS (Sample Y) GSR
Si02 16.02 31.24 65.17
A1203 6.83 6.22 14.75
Fez03 2.35 6.33 6.28
CaO 20.28 12.12 2.61
MgO 3.00 2.25 0.32
Na,0 0.30 0.58 2.02
KZO 0.59 0.32 4.22
[00117] SS Samples X and Y and GSR were subjected to processing described
above and shown in Figure 6. GSR passing through a 250 mesh sieve (63 microns)
was added to dried sludge powder before the mix was pelletized and
pyroprocessed.
[00118] The GSR powder, sieved to less than 63 microns, was added to SS
powder in selected proportions of 100%/0%, 80%/20%, 60%/40% and 40%/60%
(SS/GSR). Water was added to the mixture (up to 35% by total dry weight of the
resulting mixture) in a batch mixer until the consistency of the mix allowed
pelletization, as discussed above. The mix was fed to a revolving drum and the
pellets collected at the end of the drum were sieved through 4 and 9.5 mm
sieves.
The pellets were coated with PFA (by sprinkling), and were then dried in an
oven at
about 110 C, overnight. The resulting green pellets were then sintered in a
rotary lciln
for about 10 to about 12 minutes. The pellets formed from SS Sample X and GSR
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dusts were fired at temperatures between 920 C to 1150 C, while the pellets
formed
from SS Sample Y and GSR were fired at temperatures between 990 C to 1190 C.
RESULTS
[00119] Tables G-H, below, suinmarize the physical and mechanical properties
of aggregates formed by the process described above.
[00120] The relative dry density and water absorption of the aggregates were
determined, as described in Example 1. In this Example, coinpressive strength
was
calculated by loading individual aggregates to fracture between two parallel
plates.
Stress analysis has shown that when a sphere is tested in this way on two
diametrically opposed points the coinpressive strength 6 of the sphere is
given by the
equation:
IACS=6= 2.8P
7c * d
where "IACS" = Individual Aggregate Crushing Strength, d = sphere diameter
(min),
and P= fracture load (N). Mean values of the compressive strength were
calculated
from tests completed on at least 12 aggregates prepared at each temperature.
The load
was applied by a coinpression testing device until the aggregate fractures. A
dial
gauge on the device gives a reading indicative of the load causing fracture.
The load
was calculated from the reading by the following equations: Load (lbs) =
550.95
(Reading) - 1620.7; Load (kg) = Load (lbs)/2.205).
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[00121] Table G, below, summarizes test results for aggregates comprising
different proportions of SS and GSR at different temperatures, for the two
Samples X
and Y. The data is plotted on the graph of Fig. 1 and Fig. 10 for Samples X
and Y
respectively. Table G also summarizes IACS results for specific mixes of SS
and
GSR, at specific sintering temperatures. As discussed above, increasing the
LCSAM
concentration in the mixes (GSR in this example) resulted in a broader
temperature
interval between the initial softening, maximum densification, and complete or
near
complete melting of the samples, due to the modification of the chemical
composition
and mineralogy of the sewage sludge with the GSR dust.
TABLE G: PHYSICAL PROPERTIES OF SS/GSR AGGREGATES
Ratio Temp. Density Water IACS Ratio Temp. Density Water
(SS/GSR) ( C) (g/cm3) Absorption (MPa) (SS/GSR) ( C) (g/cm3) Absorption
Sample (%) Sample ( /a)
x y
100/0 920 1.18 44.56 125 100/0 990 1.42 38.23
930 1.44 36.84 289 1000 1.47 33.12
940 1.82 22.34 654 1010 1.51 31.89
950 2.19 3.41 885 1020 1.58 27.66
960 2.48 1.50 1067 1030 1.80 18.56
970 1.96 0.42 943 1040 2.11 8.57
980 1.70 0.15 678 1050 2.39 3.63
80/20 970 1.58 29.55 386 1060 2.29 1.11
980 1.78 21.45 612 1070 2.08 0.74
990 2.05 7.89 857 1080 1.96 0.55
1000 2.39 0.79 1048 1090 1.86 0.20
1010 2.04 0.36 1002 1100 1.7 0.12
1020 1.91 0.07 978 1110 1.60 0.11
1030 1.72 0.04 832 80/20 970 1.41 35.63
1040 1.58 0.03 675 980 1.45 32.12
60/40 1000 1.47 34.25 322 990 1.50 30.07
1010 1.49 31.52 398 1000 1.58 26.32
1020 1.52 27.56 417 1010 1.62 23.12
1030 1.65 23.74 502 1020 1.68 16.96
1040 1.88 14.12 674 1030 1.79 11.32
1050 2.11 8.24 866 1040 1.96 8.56
1060 2.38 0.82 1077 1050 2.18 6.11
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Ratio Temp. Density Water IACS Ratio Temp. Density Water
(SS/GSR) ( C) (g/cm) Absorption (MPa) (SS/GSR) ( C) (g/cm3) Absorption
Sample (%) Sample (%)
x Y
1070 2.29 0.60 1012 1060 2.34 1.03
1080 2.10 0.50 996 1070 2.48 0.46
1090 1.95 0.12 954 1080 2.28 0.12
1100 1.84 0.04 898 1090 2.01 0.1
1110 1.73 0.06 856 1100 1.84 0.04
1120 1.62 0.03 731 60/40 990 1.45 28.11
40/60 1000 1.45 29.53 378 1000 1.49 27.19
1010 1.49 28.77 412 1010 1.50 26.34
1020 1.52 26.74 477 1020 1.54 24.13
1030 1.56 24.62 523 1030 1.59 21.44
1040 1.59 21.42 589 1040 1.62 18.67
1050 1.63 18.83 621 1050 1.68 17.03
1060 1.68 18.24 665 1060 1.77 14.24
1070 1.76 13.25 736 1070 1.89 6.97
1080 1.86 9.35 803 1080 2.06 3.57
1090 2.05 5.64 962 1090 2.29 2.14
1100 2.29 2.83 1043 1100 2.44 0.58
1110 2.46 0.07 1079 1110 2.31 0.13
1120 2.38 0.67 1022 1120 2.11 0.04
1130 2.21 0.42 1008 1130 2.03 0.02
1140 2.07 0.08 998 40/60 1040 1.58 19.45
1150 1.92 0.13 962 1050 1.69 17.88
1060 1.75 14.25
1070 1.80 11.68
1080 1.85 8.25
1090 1.94 6.66
1100 2.00 4.01
1110 2.09 3.45
1120 2.22 1.97
1130 2.38 0.46
1140 2.31 0.54
[0100] The water absorptions of aggregates from mixes containing high
concentrations of SS, and more particularly Sample X, decrease rapidly with
increasing temperatures, while aggregates from mixes with higher amounts of
GSR
~ i ~nr.n~c vo rnn _ _
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show a more gradual water absorption reduction with teinperature. The IACS
show
similar trends to densities, as expected, increasing to the temperature of
maximum
densification and decreasing at greater temperatures. The increase in
aggregate
strength with increasing temperature is rapid for aggregates froin 100% SS
mixes and
becomes more gradual with increasing amounts of GSR.
[0101] Based on these results, a preferred SS/GSR mix to produce sintered
products that 'can be used in a range of applications including LWA in
concrete, is the
40%/60% SS/GSR mix for both Samples X and Y. Aggregates produced from mixes
of SS containing GSR sinter over a wider temperature range than SS alone, so
the
behavior during sintering and the final properties of aggregates may,
therefore, be
more easily controlled. The 40%/60% SS/GSR mix sintered to form a LWA, with a
density less than 2.0 g/cm3 over the temperature range of 1000 C to 1090 C,
for
example for Sample X. Aggregates with desired properties and characteristics
(porosity, density, strength) may therefore be more readily made.
[0102] As is apparent from Figs. 1 and 10 and Table G, controlling the
temperature enables production of an aggregate with a predetermined density
and
other characteristics, for a given combination of SS and GSR, when the
characteristics
and composition of SS are known. For example, using Sample Y, a 40%/60% mix of
SS/GSR, sintering at 1000 C, yielded a LWA with a density of about 1.4 to
about
1.5 g/cm3, wllile sintering at about 1110 C yielded a normal weight aggregate
with a
density of about 2.5 g/cm3.
[0103] Table H summarizes the physical (relative dry and bulk densities,
water absorptions) and mechanical properties (ACV) of sintered aggregates from
40%/60% mixes of Sample Y SS/GSR at four different temperatures, along with
the
corresponding properties of LYTAG aggregates. Aggregates produced at the
temperatures below the temperature of maximum densification had densities less
than
2.0 g/cm3, relatively low water absorptions, and high strengths. They were
therefore
well suited for use in lightweight concrete. LYTAG had a lower relative
density and
aggregate strength than these aggregates.
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TABLE H: PHYSICAL AND MECHANICAL PROPERTIES OF
AGGREGATES
Ratio Temp. Relative Water Bulk ACV
SS/GSR ( C) Density Absorption Density (%)
(g/cm3) (%) (g/cm3)
1040 1.58 19.45 0.73 18.2
1060 1.75 14.25 0.87 16.9
40/60
1080 1.85 8.25 1.09 15.3
1130 2.38 0.46 1.66 7.2
Lytag 1.48 15.50 0.85 34.2
EXAMPLE 3
[0104] In this exainple, pyroprocessed aggregates were made comprising
Sample Y SS, moderately high calcium SS (calcium oxide (CaO) of 12.12%), and
slate, which is a LCSAM (calcium oxide (CaO) 1.82%). The average chemical
analyses of Sample Y SS, and slate, which were used in these experiments, are
shown
in Table I, below. Sewage sludge Sample Y was used in these experiments. The
same equipment used in Example 1 is used here.
TABLE I: CHEMICAL ANALYSIS OF SS AND SLATE
Sewage Sludge
Constituent Slate Sample Y
Si02 58.32 31.24
A1203 28.54 6.22
Fe~03 7.23 6.33
CaO 1.82 12.12
MgO 3.67 2.25
NazO 1.45 0.58
KZO 0.88 0.32
Ti02 0.02 0.41
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[0105] The slate was subjected to processing as described in Fig. 6 and in
more detail in the previous Examples.
[0106] Sewage sludge was dried at 110 C for 24 hours before the solid cake,
being ground to fine powder. Slate was added to the sewage sludge powder in
selected proportions of 100%I0%, 80%/20%, 60%/40% and 40%/60% (SS/slate).
Water was added to the mixture (up to 45% by total dry weight of the resulting
mixture) in a batch mixer to fonn a clay-lilce mixture for pelletization.
Since slate has
a fine particle size distribution, it was directly mixed with the SS powder.
Slate might
need to be ground to a fine size before further processing witll the SS. The
resulting
green pellets were in the range of 4 mm to 9.5 mm. The pellets containing
slate, were
coated with slate powder, dried at 110 C, and fed to the rotary kiln described
above.
The resulting pellets were fired at temperatures between 990 to 1160 C for
about 10
to 12 minutes before being discharged from the kiln and allowed to cool at
room
temperature.
RESULTS
[0107] Tables J to K, below, summarize the physical and mechanical
properties of pyroprocessed aggregates from selected SS/slate mixes and
pyroprocessing teinperatures.
The relative dry density and water absorption of the pyroprocessed aggregates
was
determined as described in Example 1.
[0108] Table J summarizes physical properties results (relative dry densities,
water absorptions) and mechanical properties (IACS and ASMI). The data is
plotted
on the graph of Fig. 11. As discussed above, increasing the clay concentration
in the
mixes resulted in a broader temperature interval between the initial
softening,
maxiinum densification, and melting of the samples, due to the modification of
the
chemical coinposition and mineralogy of the SS with clay.
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TABLE J: PHYSICAL PROPERTIES OF SS/SHALE AGGREGATES
Ratio Temperature Density Water ASMI
(SS/SLATE) ( C) (g/cm3) Absorption (%)
100/0 990 1.42 38.23 1.4
1000 1.47 33.12 4.2
1010 1.51 31.89 4.8
1020 1.58 27.66 5.1
1030 1.80 18.56 7.7
1040 2.11 8.57. 12.1
1050 2.39 3.63 16.4
1060 2.29 1.11 12.6
1070 2.08 0.74 12.3
1080 1.96 0.55 11.4
1090 1.86 0.20 10.3
1100 1.71 0.12 8.8
1110 1.60 0.11 7.5
80/20 970 1.45 33.9 4.9
980 1.52 29.34 5.3
990 1.61 27.45 6.4
1000 1.67 22.34 6.9
1010 1.74 18.46 7.3
1020 1.85 12.12 8.7
1030 1.98 8.88 10.2
1040 2.06 7.23 11.9
1050 2.11 3.04 13.6
1060 2.26 1.44 15.0
1070 2.33 0.89 16.3
1080 2.13 0.23 14.1
1090 2.03 0.07 12.8
60/40 1010 1.54 28.10 5.1
1020 1.63 26.36 6.2
1030 1.69 22.32 7.3
1040 1.75 18.56 7.9
1060 1.82 16.34 8.4
1070 1.89 11.29 10.4
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Ratio Temperature Density Water ASMI
(SS/SLATE) ( C) (g/cm3) Absorption (%)
1080 1.99 7.67 11.6
1090 2.07 4.24 12.0
1100 2.18 2.13 13.2
1110 2.29 1.04 15.9
1120 2.08 0.77 15.3
1130 2.02 0.32 14.9
1140 1.89 0.03 12.8
40/60 1080 1.59 26.3 7.1
1090 1.66 22.34 8.5
1100 1.76 19.32 10.5
1110 1.82 16.35 11.2
1120 1.88 11.87 11.9
1130 1.95 8.45 12.7
1140 2.03 5.34 13.3
1150 2.11 3.23 13.9
1160 2.21 1.08 15.1
1170 2.34 0.65 16.9
1180 2.27 0.34 16.0
1190 2.16 0.12 15.5
1200 2.02 0.06 14.1
1210 1.85 0.05 13.4
[0109] The water absorptions of pellets from mixes witll high concentrations
of SS decrease more rapidly with increasing temperatures, wllile pellets from
mixes
with high amounts of clay show a more gradual water absorption decrease with
teinperature. The IACS and ASMI show similar trends to densities, as expected,
increasing to the temperature of maximum densification and decreasing at
teinperatures above that. The increase in aggregate strength with increasing
teinperature is more rapid for pellets from 100% SS mixes and becomes more
gradual
witll increasing the amount of clay in the mixes.
[0110] Based on the effect of temperature and bentonite addition on the
properties of the sintered aggregates, a 40%/60% Sample Y SS/slate mix,
sintered at a
teinperature in a range of 1030 C to 1160 C, which resulted in densities of
from about
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1.6 g/cm3 to about 2.4 g/cm3, is preferred. The behaviour of this mixture
during
sintering and the final properties of the resulting sintered LWAs may be more
easily
controlled than 100% Sample Y SS and other combinations of SS and slate,
making it
easier to manufacture. Aggregates having lower densities and higher water
absorption
may also be manufactured by processing the SS/slate pellets at lower
temperatures
than those used in these experiments.
[0111] Table K surxunarizes certain physical and mechanical properties of
aggregates from 40%/60% mix of SS/slate at three selected temperatures, along
with
the corresponding properties of LYTAG aggregates.
TABLE K: PHYSICAL AND MECHANICAL PROPERTIES
OF AGGREGATES
Ratio Temp. Relative Dry Water Bulk Density
SS/Slate ( C) Density Absorption (%) (g/cm3)
(g/cm3)
1030 1.68 19.45 0.89
40/60 1050 1.88 9.23 1.06
1110 2.39 0.74 1.64
Lytag 1.48 15.50 0.85
[0112] Aggregates may be produced with predetermined density and other
characteristics, for a given combination of SS and slate, by controlling the
temperature, as shown by Table K and Fig. 11. Liglltweight aggregates having
comparable or superior properties to LYTAG may be produced from this
coinbination, according to the required aggregate properties.
[0113] Table L suininarizes the behaviour of the pyroprocessed aggregates
resulting from the mixes of SS and slate. The temperature ranges over which
the
aggregates are pyroprocessed, the corresponding density, water absorption, and
ASMI
ranges, as well as the teinperatures of maximum densification for the
different type
and proportions of SAM to sewage sludge, are shown.
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TABLE L: CHARACTERISTICS OF AGGREGATES OF SS/SAMs
Additive Ratio Temper. Density Water ASMI Temper
SAM SS/SAM Range Range Absorption Range Maximum
( C) (g/cm) Range (%o) Density
( C)
Slate 80/20 970 - 1.45 - 0.07 - 33.9 4.9 - 1070
1100 2.03 16.3
60/40 1010- 1.54- 0.03 - 28.1 5.1- 1110
1140 1.89 15.9
40/60 1080- 1.59- 0.05 - 26.3 7.1- 1160
1210 1.85 16.9
EXAMPLE 4
[0114] In this example, synthetic aggregates were made comprising Sample Z,
low calcium SS (calciuin oxide (CaO) of 3.20%) and cement kiln dust ("CKD"), a
Group A HCSAM (calcium oxide (CaO) of 63.6%). The average chemical
composition of CKD used in these experiments is shown in Table M, below.
TABLE M: CHEMICAL ANALYSIS OF CEMENT HILN DUST
Constituent Weight (%)
CKD
Si02 14.9
A1203 3.4
Fe203 2.9
CaO 63.6
Mg0 2.3
NaZO 0.4
K20 3.2
P205 0.09
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Constituent Weight (%)
CKD
SO3 1.8
Ti02 1.1
[0115] Sainple Z SS and CKD were subjected to processing as described
above and shown in Figure 6. The SS was dried at 110 C for 24 hours and then
ground to fine powder. CK-D having a fine particle size distribution (95%
(d95) of the
volume of the particles finer than 45 microns) was added to the dried SS
powder
before the mix was pelletized and pyroprocessed.
[0116] The CKD was added to the SS powder in selected proportions of
100%/0%, 95/5%, and 90%/10% (SS/CKD). The powders were mixed with water (up
to 35% by total dry weight of the resulting mixture) in a batch mixer until
the
consistency of the mix allowed pelletization. The mix was fed to a revolving
drum
and the pellets were collected at the end of the drum were sieved through 4
and
9.5 mm sieves. The pellets were coated with CKD and then dried in an oven at
about
110 C, overnight. The resulting green pellets were then pyroprocessed in a
rotary kiln
for about 10 to about 12 minutes at temperatures between 940 C to 1110 C.
The Individual Aggregate Crushing Strengths ("IACS") were determined as
described
in Exainple 2. The coinpressive strength of individual aggregates was also
defined as
an Aggregate Strengtll Mass Index ("ASMI") as follows:
ASMI=P,
m
wllere P = fracture load (kg) and m = mass of pellet (kg). Mean values of the
compressive strength were calculated from tests completed on at least 12
aggregates
prepared at each pyroprocessing temperature and under different proportions.
RESULTS
[0117] Tables N to 0, below, summarize the physical and mechanical
properties of the aggregates formed by the process described above. The
relative dry
density, water absorption and ASMI of the aggregates were determined, as
described
in the Examples above.
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[0118] Table N, below, summarizes test results for aggregates comprising
different proportions of SS and CKD sintered at different temperatures. The
data is
plotted on the graph of Fig. 2. Table 0 summarizes physical properties results
(relative dry densities, and water absorptions from Table N) and mechanical
properties (ASMI from Table N). Increasing the CKD concentration in the mixes
resulted in a slightly narrower pyroprocessing temperature range due to
modifying the
coinposition of the initial mixture. Since CKD has such a high calcium
content, only
a small ainount was required to increase the mobility of the melts and
accelerate the
densification of the pellets of the mixture.
TABLE N: PROPERTIES OF SS/CKD AGGREGATES
Ratio Temperature Density Water Absorption ASMI
(SS/CKD) ( C) (g/cm3) (%)
100/0 980 1.92 14.26 9.8
990 1.96 12.63 10.2
1000 1.99 10.64 10.5
1010 2.08 9.32 11.1
1020 2.13 7.45 12.6
1030 2.22 3.12 13.8
1040 2.32 1.32 14.5
1050 2.39 0.85 16.3
1060 2.42 0.54 16.9
1070 2.31 0.32 16.0
1080 2.26 0.12 15.2
1090 2.19 0.07 14.7
1100 2.11 0.08 14.1
1110 2.02 0.05 13.5
95/5 980 1.68 21.45 7.6
990 1.72 19.21 8.2
1000 1.78 17.53 9.4
1010 1.83 15.42 9.6
1020 1.92 11.85 10.1
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Ratio Temperature Density Water Absorption ASMI
(SS/CKD) ( C) (g/cm) (%)
1030 - 2.01 9.02 11.4
1040 2.18 6.43 12.7
1050 2.36 1.11 14.1
1060 2.41 0.64 16.3
1070 2.29 0.43 14.8
1080 2.18 0.22 13.3
1090 2.06 0.11 12.3
1100 1.99 0.08 11.2
1110 1.87 0.07 10.7
90/10 940 1.45 27.34 4.2
960 1.50 25.99 4.9
970 1.53 23.67 6.2
980 1.58 20.11 6.6
990 1.66 18.32 7.1
1000 1.71 14.52 8.9
1010 1.77 11.44 9.6
1020 1.84 8.54 10.4
1030 1.95 5.83 12.3
1040 2.06 4.12 13.2
1050 2.19 2.03 14.4
1060 2.39 0.96 15.7
1070 2.20 0.54 14.4
1080 2.03 0.21 12.4
1090 1.92 0.11 11.6
[0119] The water absorption of the aggregates from mixes of high
concentrations of SS are lower due to the higller densities attained as a
result of the
lower ainount of fluxing agents in the mixes. The ASMI show similar trends to
densities, as expected, increasing to the temperature of maximum
densification, and
decreasing at temperatures above that. The addition of CKD in SS samples that
have
lower calcitun oxide concentrations than the Sample Z used in these Examples
is
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expected to be more significant than shown in this Example, and higher
concentrations of CK-D may need to be added to SS to achieve the desired
aggregate
composition.
[0120] Based on the effect of temperature and CKD addition on the properties
of the sintered aggregates, a 90%/10% Sainple Z SS/CKD mix, sintered at a
temperature in a range of 940 C to 1090 C, which produced pellets with
densities
from about 1.4 g/cm3 to about 2.0 g/cm3 is preferred. Such aggregates may be
used in
a range of applications including as lightweight aggregates in concrete.
However, for
the Sample Z SS used in this Example, even the 95%/5% SS/CKD mix may also be
selected for aggregate production, since the original SS already includes some
amount
of fluxes, such as calcium oxides in the composition. Aggregates having lower
densities and higher water absorptions may be manufactured when the aggregates
from the SS/CKD inix are fired at lower temperatures than those used in this
Example. The presence of fluxes in the material is believed to provide a more
improved particle packing and densification, producing aggregates with
superior
properties to pyroprocessed aggregates from material which do not contain
fluxes.
[0121] Table 0 summarizes certain physical and mechanical properties of
aggregates from 90%/10% mix of SS/CKD at three selected temperatures.
TABLE 0: PHYSICAL AND MECHANICAL PROPERTIES
OF AGGREGATES
Ratio Temp. ( C) Relative Water Bulk ASMI
SS/Clay Dry Absorption Density
Density (%) (g/cm3)
(g/cm3)
960 1.50 25.99 0.81 4.9
90/10 990 1.66 18.32 0.86 7.1
1060 2.39 0.96 1.61 15.7
[0122] As above, controlling the pyroprocessing temperature enabled
production of an aggregate with a predetermined density and other
characteristics, for
a given combination of SS and CKD.
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EXAMPLE 5
[0123] In this example, synthetic aggregates were made comprising sewage
sludge (sample Z) and limestone. The average chemical composition of the
limestone
used in these experiments is shown in Table P, below.
[0124] SS (Sample Z) and limestone powder were subjected to processing
described above and shown in Figure 6. SS was dried at 110 C for 24 hours
before
the solid calce being ground to fine powder. Limestone was added to dried
sludge
powder before the mix being pelletized and pyroprocessed.
TABLE P: CHEMICAL ANALYSIS OF LIMESTONE
Constituent Weight (%)
Si02 2.8
A1203 0.6
Fe203 0.4
CaO 53.2
MgO 0.0
IS-20 0.12
Ti02 0.0
[0125] The limestone was added to SS powder in selected proportions of
100%/0%, 95/5%, and 90%/10% and 80%/20% (SS/limestone). The powders were
mixed with water (up to 32% by total dry weight of the resulting mixture) in a
batch
mixer uritil the consistency of the mix allowed pelletization. The mix was fed
to a
revolving drum and the pellets collected at the end of the drum were sieved
through 4
and 9.5 min sieves. The pellets were coated with limestone, and were then
dried in an
oven at about 110 C, overnigllt. The resulting green pellets were then
pyroprocessed
in a rotary kiln for about 10 to about 12 minutes at teinperatures between 940
C to
1110 C.
RESULTS
[0126] Tables Q to R, below, summarize the pliysical and mechanical
properties of aggregates formed by the process described above. The relative
dry
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density, water absorption and ASMI of aggregates were determined as described
in
the previous examples.
[0127] Table Q, below, summarizes test results for sintered aggregates
comprising different proportions of SS and limestone sintered at different
temperatures. The data is plotted on the graph of Fig. 12. Table R suminarizes
physical properties results and mechanical properties of selected aggregates.
Increasing the limestone concentration in the mixes resulted in a slightly
narrower
ternperature range over which the aggregates are pyroprocessed.
TABLE Q: PROPERTIES OF SS/LIMESTONE AGGREGATES
Temperature Density Water ASMI
Ratio (oC) (g/cm3) Absorption
(SS/Limestone) (%)
100/0 980 1.92 14.26 9.8
990 1.96 12.63 10.2
1000 1.99 10.64 10.5
1010 2.08 9.32 11.1
1020 2.13 7.45 12.6
1030 2.22 3.12 13.8
1040 2.32 1.32 14.5
1050 2.39 0.85 16.3
1060 2.42 0.54 16.9
1070 2.31 0.32 16.0
1080 2.26 0.12 15.2
1090 2.19 0.07 14.7
1100 2.11 0.08 14.1
1110 2.02 0.05 13.5
95/5 980 1.75 19.45 8.4
990 1.80 16.99 9.5
1000 1.86 14.85 9.8
1010 1.92 10.75 10.3
1020 1.97 8.78 10.7
1030 2.05 6.34 12.0
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Temperature Density Water ASMI
Ratio (oC) (g/cm3) Absorption
(SS/Limestone) (%)
1040 2.21 5.32 13.3
1050 2.34 1.63 14.4
1060 2.43 0.83 16.6
1070 2.31 0.65 15.2
1080 2.19 0.40 14.4
1090 2.03 0.12 13.2
1100 1.96 0.07 12.7
1110 1.90 0.09 11.4
90/10 940 1.59 24.60 5.2
960 1.64 21.42 5.9
970 1.69 17.34 6.5
980 1.73 16.12 7.2
990 1.81 14.23 8.5
1000 1.88 10.11 9.3
1010 1.95 8.44 10.2
1020 2.02 7.23 10.9
1030 2.11 6.42 11.7
1040 2.26 3.42 12.6
1050 2.33 1.85 14.7
1060 2.39 0.75 16.2
1070 2.21 0.54 15.2
1080 2.08 0.12 14.5
1090 1.96 0.07 13.1
80/20 970 1.41 29.45 4.0
980 1.52 25.84 5.3
990 1.61 24.23 5.7
1000 1.69 20.45 7.5
1010 1.74 18.34 9.3
1020 1.85 13.24 10.1
1030 1.94 7.35 11.3
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Temperature Density Water ASMI
Ratio ( C) (g/cm) Absorption
(SS/Limestone)
(%)
1050 2.19 1-25 13.5
1060 2.41 0.97 16.2
1070 2.26 0.74 15.1
1080 2.09 0.34 14.3
1090 1.98 0.13 12.2
1100 1.85 0.11 11.8
[0128] The water absorption of aggregates from mixes with high
concentrations of sewage sludge are lower due to the higher densities attained
as a
result of the lower amount of fluxing agents in the mixes. The ASMI shows
similar
trends to densities, as expected.
[0129] The addition of limestone to SS sainples having lower calcium oxide
concentrations than the Sample Z used in this Example is expected to have a
more
significant effect than in this invention. Based on the effect of temperature
and
limestone addition on the properties of the sintered aggregates, a 90%/10%
SS/limestone mix, pyroprocessed at a temperature range of 940 C to 1100 C, to
produce aggregates having densities from about 1.6 g/cm3 to about 2.4 g/cm3 is
preferred, for use as normal weight or lightweight aggregates. However, for
the SS
sample used in this Example, even the 95%/5% SS/limestone mix could be
preferred
for aggregate production, since the original SS has already some amount of
fluxes
calcium oxides in the composition.
[0130] Table R summarizes certain physical and mechanical properties of
aggregates from 90%/10% mix of SS/limestone at three selected temperatures.
TABLE R: PHYSICAL AND MECHANICAL PROPERTIES
OF AGGREGATES
Ratio Temp. Relative Water Bulk ASMI
SS/Limestone ( C) Dry Density Absorption Density
(g/cm3) (%) (g/cm3)
90/10 940 1.59 24.60 0.84 5.2
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970 1.69 17.34 0.88 6.5
1060 2.39 0.75 1.64 16.2
EXAMPLE 6
[0131] In this exainple, synthetic aggregates were made comprising
(Sample Z) and MSW incinerator fly ash ("IFA"). The average chemical
composition
of the incinerator fly ash used in these experiments is shown in Table S,
below.
TABLE S: CHEMICAL ANALYSIS OF MSW IFA
Constituent Weight (%)
Si02 18.98
A1203 9.43
Fe203 2.35
CaO 36.02
MgO 4.12
P205 1.39
S03 2.45
K20 1.68
Na20 4.69
Ti02 1.82
[0132] SS (Sampel Z) and IFA were subjected to processing described above
and shown in Figure 6. SS was dried at 110 C for 24 hours before the solid
cake
being ground to fine powder. IFA was added to dried SS powder before the mix
being pelletized and pyroprocessed.
[0133] The IFA was added to SS powder in selected proportions of 100%/0%,
95/5%, a.nd 90%/10% and 80%/20% (SS/IFA). The powders were mixed witli water
(up to 37% by total dry weigllt of the resulting mixture) in a batch mixer
until the
consistency of the mix allowed pelletization. The mix was fed to a revolving
drum
and the pellets were collected at the end of the drum were sieved through 4
and
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9.5 mm sieves. The pellets were coated with fly ash, and were then dried in an
oven
at about 110 C, overnight. The resulting pellets were then pyroprocessed in a
rotary
kiln for about 10 to about 12 minutes at temperatures between 980 C to 1110 C.
RESULTS
[0134] Tables T to U, below, summarize the physical and mechanical
properties of aggregates formed by the process described above. The data is
plotted
on the graph of Fig. 13. Increasing the IFA concentration in the mixes
resulted in a
slightly narrower temperature interval between the initial softening, maximum
densification, and melting of the sainples, due to the modification of the
chemical
composition and mineralogy of the SS.
TABLE T: PROPERTIES OF SS/IFA AGGREGATES
Ratio Temperature Density Water
(SS/IFA) ( C) (g/cm3) Absorption (%)
100/0 980 1.92 14.26
990 1.96 12.63
1000 1.99 10.64
1010 2.08 9.32
1020 2.13 7.45
1030 2.22 3.12
1040 2.32 1.32
1050 2.39 0.85
1060 2.42 0.54
1070 2.31 0.32
1080 2.26 0.12
1090 2.19 0.07
1100 2.11 0.08
1110 2.02 0.05
95/5 980 1.82 15.54
990 1.85 13.97
1000 1.90 11.74
1010 1.95 9.11
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Ratio Temperature Density Water
(SS/IFA) ( C) (g/cm) Absorption (%)
1020 2.08 7.35
1030 2.14 5.33
1040 2.29 2.11
1050 2.35 0.89
1060 2.41 0.56
1070 2.29 0.33
1080 2.18 0.12
1090 2.11 0.1
1100 2.01 0.08
1110 1.97 0.06
90/10 970 1.60 20.35
980 1.69 17.33
990 1.76 15.63
1000 1.82 11.21
1010 1.88 8.34
1020 1.99 5.53
1030 2.05 4.23
1040 2.14 2.66
1050 2.30 1.43
1060 2.43 0.66
1070 2.30 0.43
1080 2.21 0.23
1090 2.09 0.15
1100 1.96 0.08
1110 1.89 0.05
80/20 980 1.54 26.34
990 1.58 23.5
1000 1.63 21.53
1010 1.75 17.34
1020 1.86 13.24
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Ratio Temperature Density Water
(SS/IFA) ( C) (g/cm) Absorption (%)
1030 1.92 8.45
1040 2.01 5.35
1050 2.19 3.22
1060 2.38 0.75
1070 2.23 0.53
1080 2.08 0.23
1090 1.94 0.12
1100 1.85 0.06
1110 1.76 0.04
[0135] Based on the effect of temperature and IFA addition on the properties
of the aggregates, a 80%/20% SS/IFA mix is preferred to produce aggregate
having
densities between 1.5 g/cm3 to 2.4 g/cm3. However, the 90%/10% SS/IFA mix,
over
the saine pyroprocessing temperature range is also preferred.
[0136] Table U summarizes certain physical properties of aggregates from
80%/20% mix of SS/IFA at three selected temperatures.
TABLE U: PHYSICAL AND MECHANICAL PROPERTIES
OF AGGREGATES
Ratio Temp. Relative Dry Water Bulk density
SS/IFA ( C) Density Absorption (%) (g/cm)
(g/cm3)
960 1.54 26.34 0.80
80/20 1000 1.63 21.53 0.83
1060 2.38 0.75 1.56
EXAMPLE 7
[0137] In this example, synthetic aggregates were made comprising SS
(Sainple Z) and granulated blast furnace slag ("GBFS"). The average chemical
coinposition of GBS used in these experiments is shown in Table V, below.
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TABLE V: CHEMICAL ANALYSIS OF GGBS
Constituent Weight (%)
Si02 32.6
A1203 12.8
Fe203 1.1
CaO 41.3
MgO 5.3
SO3 1.9
K20 0.7 '
Na20 0.44
Ti02 0.6
[0138] SS (Samples Z) and GBS were subjected to processing described
above and shown in Figure 6. SS was dried at 110 C before the solid cake being
ground to fine powder. GBFS was added to dried sludge powder before the mix
being
pelletized and pyroprocessed.
[0139] The GBS was added to sludge powder in selected proportions of
100%/0%, 95/5%, and 90%/10% and 80%/20% (SS/GBS). The powders were mixed
with water (up to 35% by total dry weight of the resulting mixture) in a batch
mixer
until the consistency of the mix allowed pelletization. The mix was pelletized
and the
pellets were sieved through 4 and 9.5 mm sieves. The pellets were coated with
GBS,
and were then dried in an oven at about 110 C, overnight. The resulting
pellets were
pyroprocessed in a rotary kiln for about 10 to about 12 minutes at
temperatures
between 970 C to 1110 C.
RESULTS
[0140] Tables W to X, below, summarize the pliysical and mechanical
properties of aggregates formed by the process described above. Table W,
below,
suminarizes test results for aggregates comprising different proportions of SS
and
GBS fired at different teinperatures. The data is plotted on the graph of Fig.
14. A
1 1 lntd'lc 110 nnn
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similar effect as CKD, IFA, and limestone was observed for increasing GBS
concentration in sewage sludge mixes.
TABLE W: PROPERTIES OF SS/GGBS AGGREGATES
Ratio Temperature Density Water
(SSGGBS) ( C) (g/cm) Absorption (%}
100/0 980 1.92 14.26
990 1.96 12.63
1000 1.99 10.64
1010 2.08 9.32
1020 2.13 7.45
1030 2.22 3.12
1040 2.32 1.32
1050 2.39 0.85
1060 2.42 0.54
1070 2.31 0.32
1080 2.26 0.12
1090 2.19 0.07
1100 2.11 0.08
1110 2.02 0.05
95/5 980 1.75 17.43
990 1.82 14.80
1000 1.87 13.22
1010 1.91 10.85
1020 1.99 8.33
1030 2.11 5.73
1040 2.29 2.60
1050 2.38 1.04
1060 2.44 0.78
1070 2.26 0.55
1080 2.17 0.32
1090 2.07 0.12
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Ratio Temperature Density Water
(SSGGBS) ( C) (g/cm3) Absorption (%)
1100 1.99 0.07
1110 1.94 0.03
90/10 970 1.58 23.35
980 1.67 19.24
990 1.74 17.34
1000 1.82 13.24
1010 1.89 9.34
1020 1.97 6.21
1030 2.07 4.15
1040 2.18 2.43
1050 2.31 1.05
1060 2.42 0.45
1070 2.31 0.13
1080 2.22 0.09
1090 2.10 0.04
1100 1.97 0.02
1110 1.91 0.02
80/20 980 1.50 28.22
990 1.59 23.421
1000 1.64 20.4
1010 1.72 17.85
1020 1.85 12.97
1030 1.93 8.34
1040 2.03 4.89
1050 2.20 3.11
1060 2.39 0.67
1070 2.25 0.23
1080 2.09 0.09
1090 1.92 0.07
1100 1.86 0.03
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Ratio Temperature Density Water
(SSGGBS) ( C) (g/cm) Absorption (%)
1110 1.78 0.02
[0141] Based on the effect of temperature and GBS addition on the properties
of the produced aggregates, a 80%/20% SS/GBS mix, sintered between 980 C to
1110 C to produce aggregate having densities from about 1.5 g/cm3 to about
2.4 g/cm3, is preferred. However, for the SS Sample Z used in this Example,
even the
90%/10% SS/GBS mix may also be effective for aggregate production, since the
original SS has already some amount of fluxing components, such as calcium
oxides,
in the composition.
[0142] Table X summarizes certain physical properties of aggregates from
80%/20% SS/GBS pellets.
TABLE X: PHYSICAL AND MECHANICAL PROPERTIES
OF AGGREGATES
Ratio Temp. Relative Dry Water Bulk
SS/GGBS ( C) Density (g/cm3) Absorption (%) Density
(g/cm3)
980 1.50 28.22 0.81
80/20 1000 1.64 20.40 0.84
1060 2.39 0.67 1.59
EXAMPLE 8
[0143] In this example, synthetic aggregates were produced from mixes of the
low calcium silicoaluminous materials pulverized fuel ash and London clay,
with the
higll calcium silicoaluminous materials granulated blast furnace slag ("GBS"),
and
lime waste. The GBS was ground. Waste glass was also used in mixes as either a
low calciuin silicoaluminous material or a high calcium silicoaluminous
material.
The average composition of waste glass and the clays bentonite and kaolin are
given
in Examples 1 and 3, above, respectively. Significant constituents of PFA and
GBS
are given in Table Z1 below.
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TABLE Zl: CHEMICAL ANALYSIS OF PFA AND GBS
Constituent Weight (%) Weight (%)
PFA GBS
Si02 52 35
A1203 26 11
Fe203 8.6 1
CaO 1.9 41
[0144] Since these materials had fine particle size distributions, they were
directly mixed witlz each other witllout milling. In mixes not containing clay
low
calcium silicoaluminous material, clay was added as a plastic binder in
proportions
ranging from 10% to 30% by dry weiglit of the total weight of the mixture.
Table Z2
gives the materials and their proportions used for aggregate production, where
low
calcium silicoaluminous materials are identified as Material 1 and high
calcium
silicoaluminous materials are identified as Material 2.
TABLE Z2: COMPOSITION OF AGGREGATE MIXES
Materiall Material 2 Material 3 Ratio 1/2 Ratio 1/2/
PFA Glass Clay 80/10/10
PFA Glass Clay 70/20/10
PFA Glass Clay 60/20/20
PFA Glass Clay 50/30/20
PFA Glass Clay 40/30/30
PFA Glass Clay 40/50/10
PFA Glass Clay 30/60/10
PFA Glass Clay 20/70/10
PFA GGBS Clay 80/10/10
PFA GGBS Clay 70/20/1 C
PFA GGBS Clay 60/20/2C
PFA GGBS Clay 50/30/2C
PFA GGBS Clay 40/30/3C
PFA GGBS Clay 40/50/1 C
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Materiall Material 2 Material 3 Ratio 1/2 Ratio 1/2/3
PFA GGBS Clay 30/60/10
PFA GGBS Clay 20/70/10
Clay Lime waste 70/30
Clay Lime waste 50/50
Clay GGBS 80/20
Clay GGBS 70/30
Clay GGBS 60/40
Clay GGBS 50/50
Glass GGBS 40/60
Glass GGBS 30/70
Glass GGBS 20/80
[0145] The materials were mixed in the above proportions and pelletized with
the addition of water using the equipment described in the Examples above. The
pellets were then dried in an oven at about 110 C, overnight. The resulting
pellets
were then pyroprocessed in a trefoil rotary lciln shaped like a three leaf
clover using
fuel propane for about 15 to about 20 minutes at temperatures between about
1000 C
to about 1250 C. The aggregates were air-cooled.
[0146] The aggregates retained their integrity when removed from the lciln.
They were nearly spherical or slightly angular and varied in color depending
on the
mix. For example, aggregates comprising high amounts of GBS appeared whitish,
wl7ile aggregates containing high amounts of PFA appeared to be dark brown.
The
aggregates had a hard smooth surface and were lightweight. They had a
relatively
hard structure when randomly crushed.
The embodiments described herein are examples of implementations of the
invention. Modifications may be made to these exainples without departing from
the
spirit and scope of the invention which is defined by the claims, below.
