Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CLEANSING CONTAMINANTS FROM A IiETEROGENEOUS MATERTAL USING A SORPTION
AGENT
The present invention relates to a process for
cleansing contaminants, such as oil, PCB, PAH, heavy
metals, lipids and the like from a heterogeneous material,
such as sand, gravel, earth, oil gravel, asphalt, drill
borings ("kaks"), sewage sludge and the like.
Contamination of dissimilar materials for example in
connection with industrial equipment, dump locations or
beaches which are contaminated by for example an oil
spill, is a well known and increasing problem, and large
resources are employed to find solutions to purifying such
masses. The solutions must be able to be carried out
practically and economically. Several reports describe big
environmental problems connected with such contaminated
materials. In this connection various hydrocarbon com-
pounds are often mentioned such as oil-like compounds,
hydrocarbons which either have coupled on chlorine or
bromine groups (PCB), or dissimilar types of aromatic com-
pounds (PAH). The said compounds are all soluble in non-
polar solvents. That is to say they are dissolved slightly
in water, and in an association that will be energetically
favourable to exclude water. By virtue of the water-re-
pelling property these media will readily adhere to solid
surfaces, such as stone, gravel and earth. Furthermore
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water which runs through these materials will not wash away or
dilute these hydrophobic solvents.
s A number of locations are mapped where such contaminated
materials constitute a significant environmental problem.
In addition to the materials consisting of hydrophobic
contaminants they will also consist of various heavy metals,
which because of their toxicity also represent an
1o environmental problem.
To-day it is usual to "clean" such dump materials by
combusting the contamination of the stone materials. However
this is very expensive since the costs of such burning off is
related to the weight of the materials and to the combustion
s5 value, that is to say how much energy which can be utilised by
such a combustion. Materials from industrial sites or dumps
consist mainly of stone/gravel, that is to say the weight is
high and the combustion value low.
There is therefore a need for alternative solutions.
2o Such a solution is described in WO 97/04623 which relates to
a sorption agent comprising the plant family Sphagnum for
the sorption of hydrophobic compounds where the sphagnum
plant is substantially wholly or partially dried. The
publication also describes the application of the plant
25 material for removing hydrophobic compounds from solutions
and emulsions, together with it being employed directly on
materials which are contaminated with hydrophobic compounds
by being rubbed against the material. For example it is
mentioned t$at the plant material can be rubbed directly
3o against an oil spill for example in a workshop hall.
However there are other problems which must be solved in
order to cleanse contaminants from a heterogeneous material,
such as stone and earth. In such materials the oil is an
integrated part of the material, that is to say it envelops
35 and sticks together with the dissimilar components of the
material so that it becomes a relatively
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viscous, tacky material. Furthermore the material is
formed of particles of relatively small size so that one
cannot apply the moss for example to "dry" the particles
as one for example can dry off a workshop floor.
The present invention aims therefore to produce a
solution for cleansing such materials. When an effective
absorptive or adsorptive material is added to a material,
and the material and the sorption material are kneaded and
tumbled together a certain time, the contaminants will,
whether they are hydrophobic compounds or for example
heavy metals, be transferred from the material to the
sorption agent, assuming that the sorption agent has
stronger ad- and/or absorptive properties than the
material, and that the compounds are detached from the
material by the friction which is created during the
kneading/tumbling process, or by means of water/solvents.
Even for an effective sorption agent this will not be
added if the contaminants are solidified and very strongly
fixed to particles of the material. Also this problem is
aimed to be solved with the present invention.
A further problem in the cleaning of such materials
is that the material, such as sand, gravel and earth, with
respect to the size of the particles constitutes a hetero-
geneous mixture, and often comprising a significant pro-
portion of smaller particles, right down to a size of only
some few microns in diameter. A problem which cannot be
solved with the afore-mentioned invention is therefore
separating the sorption agent from these in part very
small particles. The present invention therefore aims to
solve this problem also.
The present invention describes therefore a process
for cleaning various types of materials, such as for
example fill materials, gravel, earth and the like by
removing the dissimilar contaminants, such as hydrophobic
contaminants as for example oil, PCB and PAH, and heavy
metals from the materials.
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By the term "material" is designated any type of
material, such as fill material, oil gravel, asphalt,
drill cake, sewage sludge, gravel, sand, earth and the
like.
The term "sorption agent" designates an agent which
has absorptive and/or absorptive properties, that is to
say properties for absorbing a compound or adhering to the
surface, and/or integrated in the structure of the agent.
The term "solid contaminants" designates contaminants
which are relatively strongly adhered to the material.
Typically such solid contaminants must be dissolved from
the material by applying a non-polar and/or polar solvent.
The present invention describes a process which is
characterised by the steps:
c) that a sorption agent is added to the material, and
that the material and the sorption agent are mixed/kneaded
sufficiently for a considerable portion of the contaminant
to be extracted from the material and absorbed by the
sorption agent, and that
e) the sorption agent is thereafter separated from the
material on the basis of specific gravity/particle size by
means of an applied gas flow, such as a stream of air, so
that the sorption agent is led with the flow and can be
collected in a separate fraction.
Further modifications of the invention are evident
from the steps:
a) which consists in adding to the material a non-polar
solvent, which dissolves "solid" contaminants in the
material and makes them soluble in the fluid fraction, and
that thereafter the fluid fraction is separated from the
material, for example by filtration, decanting, centri-
fuging and the like, and
b) which consists in adding to the material a polar
solvent, such a water, added to one or more detergents,
which dissolve "solid" contaminants so that these are made
soluble in the fluid fraction, and that thereafter the
fluid fraction is separated from the material, for example
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by filtering, decanting, centrifuging gad the'like and
d)' which consists in drying the material for example by
applying an air flow, a~/or that the material is: heated.
In one embodiment the above process is characterized in
5 that the kneading/mixing consists in interacting the material
and the agent (solvent or sorption agent) in-a rotating drum
having a speed and a time period which is adapted to. the
contaminated material which is to be cleansed, and the solvent
and/or sorption agent which is utilized. The drum may rotate
with a speed in the range of 5-100 revolutions per minute,
preferably 20-40 revolutions per minute, and that the drum
time is (roan 1-600 minutes, preferably 5-20 minutes.
In yet another embodiment the process of the invention
may be characterized in that the non-polar solvent can be any
_polar liquid solvent, or a mixture of several non-polar ,
solvents, such as diesel, paraffin, white spirit, alkaaes,
alkenes, alkyaes, alcohols, organic acids, aromatic compounds
and the like. A mixture~comprising material and non-polar
solvent may be heated to a temperature which depends on the
boiling point of the solvent, the temperature being chosen to
be in the range of 0°C to just below the boiling point of the
solvent.
In yet a further embodiment of the present invention the
grocers is characterized in that the polar solvent can be
preferably any polar liquid solvent, such as water, comprising
one or more detergents, such as mixtures like soap, washing
agents and the like, or more characterized detergents such as
cationic, anionic, zwitterionic or non-polar detergents. The
process is further characterized in that the material and
solvent may be heated to a temperature in the range of 0-98°C,
preferably in the range of 30-50°C.
In yet a further embodiment of the present invention the
above process may be characterized in that the sorption agent
comprises.chemical and/or biological agents, a sorption agent
having a specific gravity which is sufficiently leas than the
specific gravity of the material so that the sorption agent
including the contaminant can be blown off, and is separated
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5a
from the material, with a flow of gas, and that the strength of the
gas flow can be adjusted and adapted according to the agent and the
properties of the material so that an effective separation is
achieved. Furthermore the sorption agent may be biologically
degradable and/or combustible and may also comprise bark, moss or
peat which is in advance partially dried.
In yet a further embodiment of the present invention the
process may be characterized in that the sorption agent
comprises Sphagnum plants and/or peat. The sorption agent of
the present invention may be processed so that it consists of
particles having a size in the range of 0-20 mm, preferably
0.1-0.5 mm.
A preferred embodiment is therefore to mix together
the sorption agent and a contaminated material so that the
contaminants are transferred to the sorption agent.
Preferably this is carried out in a rotating drum. For the
mixing/kneading to be effective it is an advantage, but not
a necessity, that the drum is equipped with a number of
blades, so that the material and the agent are thoroughly
mixed. When a sufficient quantity of the contaminant is
transferred to the sorption agent these two fractions must
be separated from each other. According to the invention
this is carried out by blowing a current of air through the
mixture. One way this can be carried out is that the drum
with blades rotate during the blowing operation. The blades
will then lift the material so that separation is made more
efficient. Alternatively the current of air can for example
be blown directly through the mixture. The strength of the
air current is adapted to the two fractions which are to be
separated.
Various types of sorption agents, such as chemical or
biological, can be utilised. A preferred solution is to
employ bark, peat or moss since these are materials which
have a low specific gravity, and are both combustible and
biologically degradable. The greater the difference is
between the specific gravity of the particles in the
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5b
material and the specific gravity of the garticl,e~ of the
sorption agent, the more effective is the separation pro-
cess, that is to say the smaller the strength of the air
flow that is required for blowing off the sorption agent,
and the smaller the proportion of the smallest particles
in the material that will be transferred to the sorption
agent fraction. In addition to specific gravity the par-
ticle size is an important parameter in the separation
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process, and it has been found that if the sorption agent
particles are of small size so the separation is more
effective. If the sorption agent is for example moss so it
will be more favourable to cut this up into small par-
titles.
In addition to the direct mixing of material with
sorption agent it will be favourable in a number of cases
to add a solvent to the material to dissolve and remove a
portion of the contaminants before the sorption agent is
added. Both non-polar and/or polar solvents can be
utilised, and the sequence is determined from the type of
contaminant which is to be cleansed from the material.
When the solvent has taken effect for a time on the
material, generally during the tumbling/kneading where
length depends on the type of contaminant and solvent, the
fluid fraction is separated from the solid particles with
filtering, centrifuging, decanting or in another manner.
In order to increase the solubility of the cont-
aminants it is often favourable to heat the mixture of
20. material and solvent. This is tarried out in a known
manner, not indicated further.
After the material is treated with solvent, one or
more times, so the sorption agent is added. The mixture is
kneaded/tumbled so that the sorption agent absorbs the
contaminant, and possibly residues of solvent. Thereafter
it can be favourable to reduce the moisture content of the
sorption agent before the separation process starts. This
can be carried out either by air drying, for example by
blowing an air current into the mixture, or by heating the
mixture, for example due to the drum being equipped with a
heating element, possibly a combination of these methods.
The cleansing process according to the invention is
specified in some illustrating examples.
Example 1
7962 grams of a black, viscous and sticky oil gravel,
consisting of particles of an order of magnitude of 5 - 50
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mm are kneaded/mixed in a drum (about 150 litres) together
with 1952 grams of diesel oil. The type of oil gravel which is
used includes about 10 weight per cent of oil. The object is
s to remove the oil from the stone/gravel particles. The
material and diesel are tumbled together for 5 minutes at a
speed of 27 revolutions per minute. The fluid fraction (1598
grams) is strained off (run off time 3 minutes). Thereafter a
water solution consisting of 102 grams washing agent/detergent
so (ZaloTM) and 985 grams of water is added. The mixture is
tumbled for 5 minutes, and the water fraction (1152 grams) is
strained from the gravel fraction (run off time 3 minutes).
In these two steps large portions of the oil are now
removed. However the gravel particles are coated with a film
s5 consisting of detergent/oil/water. If this mixture is dried
by evaporating the water the oil will continue to remain as a
film on the gravel particles, and thus the problem will not
be satisfactorily solved.
To this mixture (detergent/oil gravel/water), where
2o the amount of water is now 1265 grams there is added 1109
grams, dried Sphagnum moss. The moss is cut up and consists
of particles having a size in the range of 0.1 - 10 mm. The
mixture is tumbled for 15 minutes. Thereafter the moss is
blown away, that is to say separated from the gravel fraction
25 with an applied current of air, and a visual characterization
of the gravel particles shows that nearly all the oil has
gone. Residues of the oil cannot be seen on the gravel
particles.
Example 2
3o Ditch gravel (10026 grams), which is gravel/sand
particles having a size in the range of 0.1 - 10 mm, and a
moisture content of about 10%, is added to Troll - crude oil
(956 grams). To this mixture of oil and gravel is added
Sphagnum moss (735 grams) in particulate form (0.1 - 10 mm).
35 The mixture is tumbled for 15 minutes. The moss particles are
blown off, and the gravel fraction appears
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completely clean, free from oil and moss, while the moss
fraction is free of gravel particles. However there is a
slight odour of oil from the gravel particle fraction.
Example 3
Ditch gravel (10832 grams), of the same type as above,
is added to Trolls crude oil (699 grams). To this mixture
there is added a mixture of water (1056 grams) and washing
agent, of the Zalo type, (101 grams). The mixture is
so mixed/kneaded in a rotating drum for 10 minutes. Thereafter
the water is removed. Run off 5 minutes. To the mixture is
added 684 grams moss; and it is tumbled for 10 minutes. The
moss fraction is blown off. The gravel mixture appears
completely clean, and no odour of oil is observed from this
i5 fraction now. The moss is free of gravel particles.
In relation to Example 2 the extra washing step which is
introduced has caused the moss to become somewhat cleaner. The
reason for this is that the detergent/water mixture which is
employed dissolves, that is to say makes water- soluble, the
20 oil fraction which is most strongly adhered to the gravel
particles.
Example 4
Brown earth (11312 grams) having a particle size in
25 the range of from 0.1 - 10 mm, and having a moisture content
of about 15o is added to Troll' - crude oil (953 grams). To
this mixture is added 794 grams moss in particulate form.
There is tumbling for 20 minutes, after which the moss is
blown off. The earth fraction appears completely clean, only
3o a slight odour of oil, and consists of spherical particles
(0.2 - 1 cm). The moss fraction does not contain earth
particles.
The Example with earth is conducted in order to
illustrate how for example sewage sludge can be treated in
35 order to cleanse this for example of heavy metals. The
Examples show that a process in accordance with the
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present invention can clean a material which is cont-
aminated by various types of compounds. Very often such
materials consist however of various oil-like compounds,
and the Examples are therefore carried out by utilising
oil. By a visual characterization it is assumed that the
gravel/earth fractions include less than 0.1% oil, that is
to say that more than 99% of the oil is removed. By a
correct adaptation of the air pressure during the
separation the moss fraction is not contaminated by
stone/earth particles.
There is in progress now a chemical characterization
of the various fractions. The effect which is achieved
with the method is very surprising, and makes a parti-
cularly important contribution to the possibility of
taking care of the environment in a better manner by
effectively clearing it of contaminated materials.
Dried Sphagnum moss is a material of very low
specific gravity, and relative to stone/gravel the speci-
fic gravity of the moss is considerably less. Even after
the moss has absorbed the oil contamination the specific
gravity is considerably lower than for stone/gravel. This
fact is employed in order to separate the oil-containing
moss from the gravel particles.
Since the quantity of water in the sorption agent
will be reduced during drying an effect is obtained pro-
portionate to composting and/or combustion of the sorption
agent in that the weight of the contaminant-containing
fraction is reduced. Costs of composting and combustion
are related to the weight of material. In addition the
costs are related to the combustion value of the material,
and this will also increase as the moisture content of the
material is reduced.
By utilising the separation technique according to
the present invention the gravel fraction which is left in
the drum after the cleaning process will be nearly
completely clean, both with respect to oil, diesel, water
and sorbent. The sorbent has correspondingly absorbed
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nearly all the oil, the diesel and the water, except that
this fraction is not significantly contaminated with
gravel particles to a particular degree.
In this way there are two fractions which can be
5 treated in a dissimilar manner. The gravel fraction can be
employed as if it were free of contamination. The moss
fraction can be either composted or burned. The big gain
lies in the contamination being transferred to a much
lighter fraction, which can be processed much more simply,
10 cheaply and better than the contaminated gravel fraction.
The process according to the invention will also be
able to be employed for cleansing heavy metals and oil
from the gravel fractions in drill borings ("kaks"). Drill
borings is a collective term for the fraction which is
taken up in the boring of new bore holes and consists
largely of stone/gravel particles released in a fraction
of drill sludge. The sludge is separated from the borings
by known methods, but the problem is that the borings
include a coating of oil-type compounds and heavy metals.
By mixing these drill borings with a sorption agent and by
using the process according to the invention these cont-
aminants can be removed from the borings. On cleansing
bore drillings the process can also include the step (b)
so that the heavy metals are dissolved in a watery
fraction, in order thereafter to be absorbed by the sor-
bent together with the water. Thereafter the water is
dried off by heating/air flow so that the heavy metals are
concentrated in the sorbent. In this way the heavy metals
and the oil compounds are separated from the borings, and
cleansing of such borings is therefore comprised by the
scope and idea of the invention.
