Note: Descriptions are shown in the official language in which they were submitted.
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IN SITU IMMOBILIZATION WITHIN DENSITY VARIANT
BODIES OF WATER
BACKGROUND OF THE INVENTION
This invention relates to methods for in situ immobilization of metals in
water and earthen boundaries bordering the water as well as to immobilization
treatment of metals in water having varying density zones to access and treat
all
regions within the water and at the water-earthen boundaries.
Waste stacks are generated by many types of industrial processes, often
as a result of the extraction of valuable materials. The waste stacks are
frequently piles of economically invaluable material left over from the
industrial
processes. For instance, power plants often generate waste stacks of ash. The
ash
is left over when energy is extracted from fuel by burning. Mining processes
also often generate waste stacks. The waste stacks contain minerals left over
after a valuable metal or mineral is extracted from the mined earth materials.
For
example, phosphorus mines often result in waste stacks containing
predominantly gypsum as a processed waste. The waste stack gypsum is a
relatively invaluable mineral left over after phosphorus is removed from the
mined materials.
In many instances, waste stacks are formed as follows. First, the
residual or waste material is combined with water to form a waste slurry. This
waste slurry is then flowed to a settling pond where the solids contained in
the
waste slurry settle out. Water evaporates or permeates from the settling pond.
Over time, the settled solids leave behind a stack of waste material. Some
water
is retained in the settled waste material which makes up the waste stack. This
process of deposition settling and evaporation is repeated until the resulting
waste stack is too large for the process to economically continue, or is
terminated for other reasons. If needed, a new waste stack is started and
grows
in a similar fashion. FIG. 1 shows a mine 12 which has been in operation for a
significant period of time and is surrounded by a number of waste stacks 14.
The
individual waste stacks 14 are often huge, frequently comprising millions of
cubic yards. The amount of material currently stored in waste stacks is
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2
enormous, and it continues to increase as mining and other industries continue
to
produce and develop new operations.
A problem associated with waste stacks is toxic metal migration. The
actual percentage of water-soluble toxic metals in a given waste stack is
usually
very small; for example, less than 1.0 percent. Because the waste stacks are
often very large, however, the total amount of toxic materials in a waste
stack is
often large enough to present some risk to surrounding areas and ground water.
These risks arise in part due to potential metals migration of liquids from
the
waste stack. The slurry water may percolate into the soil in addition to
evaporating or remaining in the waste stack.
Toxic metals potentially found in waste stacks include but are not
limited to Pb, Hg, U, Cd, Fe, As, Se, Cu, Cr, Ni, Zn, Co, Mn, and Ag. Over
time
such metals can ]each out of the waste stacks and into ground water. Thus, it
is
desirable to keep the metals within or near the waste stacks to minimize the
danger posed by such metals.
Keeping the metals within or near the stack is often difficult, especially
since the metals may be present in water-soluble forms. Such water-soluble
forms can migrate as metal solutes whenever water moves through the stacks.
Since the stacks are frequently exposed to water, either in the form of rain
or in
the form of wastewater deposited on the stacks, water-soluble metals or metal
compounds present in the stacks are exposed to conditions that may encourage
their migration. In some situations, metals have already begun migrating out
of
existing waste stacks and into a boundary zone or layer below the waste
stacks.
Thus, it is desirable to have a method which will not only inhibit further
migration of metals from the waste stacks, but which will also inhibit the
migration of metals that are in a boundary layer beneath the waste stacks.
One method for containing metals within a waste stack has been to treat
the waste stack with microbes that are capable of producing microbial
sulfides.
The microbial sulfides are sulfide byproducts of microbial activity in waste
stack affected zones. The microbial sulfides react with metal ions or metal
containing compounds contained in the waste stack affected zones to form metal
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3
sulfides. The metal ions or metal containing compounds contained in the waste
stack affected zones become relatively insoluble during this treatment and are
inhibited from migrating within or from the waste stack affected zone. This
method was first disclosed in U.S. patent No. 5,632,715, which is incorporated
herein by reference. This method has been applied successfully in treating
waste stacks and inhibiting migration of metals within boundary areas within
such waste stacks.
With the excavation of mining materials during the mining process, a
void is typically created that is often filled with water. These large water-
filled
zones, typically known as pit lakes 15, contain many of the same type of
contaminants as are found in waste stacks, especially when the lake is
adjacent a
waste stack from the mining operation. Additionally, the pit lakes have soil
boundaries along the surface as well as extending down to the bottom of the
lake. Metal migration continues to occur within the soil boundaries between
the
water and the soil. Further still, the water from the pit lakes can seep into
adjacent water tables, which can result in the contamination of water systems
in
populated areas.
One prior art method of treating such bodies of water has been to pump
the water from the lake source to a process treatment plant and then return
the
treated water to the pit lake. Another method in the prior art for treating
such
bodies of water has included taking the process treatment plant to the body of
water and placing it on a boat that travels across the surface of the pit lake
to
treat the water at the surface level and return the treated water back to the
surface.
There are several problems that exist in either solution. Firstly, both
treatment solutions are expensive to conduct, as the cost of pumping the water
alone can be extreme. Secondly, mixing treated water with contaminated water
only causes the contaminated clean water to be re-contaminated, or require
there
be a secondary storage facility, which is not always available or suffers from
the
same soil contamination of the first pit lake. Thirdly, the plant operators
must
be on the water in the process on the lake method, which potentially exposes
the
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operators to the contaminated water unnecessarily. Fourthly, these treatment
solutions are at times unable to reach the depths of these pit lakes, which
can
have depths ranging from 50 feet to as great as 3,000 feet. Again, water
pumping becomes expensive for deep pit lakes. Fifthly, certain water-filled
workings are completely subterranean and are virtually impossible to access
directly or the water is so deep that pumping the water from the subterranean
cavity to the surface for treatment becomes cost prohibitive.
Not only must the water be treated in such conditions, but so to must
the soil boundary within either the subterranean pit lake or the open body pit
lake also be treated during the treatment process. The prior art methods of
removing the water for treatment at a separate location, or merely treating
the
water on the surface of the pit lake fails to treat to treat the soil boundary
of the
lake simultaneously with treating the water.
Accordingly, there is a need within the industry to be able to treat
contaminated water sources, such as pit lakes and subterranean mine cavities
filled with water, in an economical and environmentally sound way that also
includes treating the soil boundaries adjacent the water.
SUMMARY OF THE INVENTION
According to the present invention, an in situ method for treating large
bodies of water having varying density strata to immobilize contaminant metals
within the water is disclosed. The method is also able to treat the soil water
boundary within the pit lake to provide additional immobilization. The pit
lakes
can include open pit lakes, subterranean mine lakes, flowing streams and the
like. The method is also able to treat an abandoned mine prior to the filling
of
the mine with water. The invention also contemplates treating bodies of water
having varying density strata.
The method, or process for in situ immobilization of metals is focused
on treating large bodies of water having metals therein that are also adjacent
a
border of soil or earthen materials in an attempt to immobilize the metals
from
penetrating through the soil. Initially, the density mean of the body of water
is
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determined, which is densest typical at regions at or approaching 4 degrees C.
The process includes introducing a treatment substance that has a density
greater
than that of the density means into the body of water, providing at least one
microbe proximate or in the body of water, producing microbial sulfides
arising
5 from the initial microbe placement, causing microbial sulfides to react in
situ
with metal ions or metal containing compounds located within the body of
water, reducing the solubility of the metal ions by forming metal sulfides,
and
inhibiting the migration rate of the metal ions or other metal containing
compounds within or from the soils or earthen materials as they settle out of
the
water. The treatment substance typically includes at least one microbe
nutrient
to sustain activity of the microbes added thereto. The microbial activity
yields
microbial sulfides that react with the contaminants within the water to form
the
metal sulfides.
The treatment can include more than one supplemental feeding of the
treatment substance and the treatment substance can be either in liquid or
powder form, which dry powder form may include pellets ranging in the size
from one millimeter to 300 millimeters in diameter. The pellets, in larger
size
form, can be processed to have an average density larger than the density mean
of the water so that the weigh of the pellets carries them past the densest
regions
within the water and dissolve at a rate suitable for dispersal of the
treatment
substance throughout the body of water.
The treatment substance, or fluid, is also buffered so as to balance the
pH of the water being treated within a range of 6 to 8 pH. Accordingly, the
treatment substance includes a treatment fluid having a pH range of about 1 to
12 in order to buffer the water during application. The microbes that are
relied
upon to generate the microbial sulfides can also occur naturally within the
body
of water or within the soils or earthen materials.
The treatment substance is also designed to specifically exclude
cysteine. The sulfides typically react with contaminant metals including AS,
SE,
CD, HG, CU, CR, U, FE, ZN, PB, NI, CO, MN, and AG.
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The treatment substance is further characterized to include a
concentration of a carbohydrates to serve as microbial nutrients. The
carbohydrate has a concentration of up to 10 grams per liter of fluid to be
treated
and can further include up to 0.1 grams of total nitrogen per liter of fluid
to be
treated. Further still, the treatment substance can also include about 0.25
grams
of phosphate ion per liter of fluid to be treated or a combination of
carbohydrate,
phosphate ion, and total nitrogen. The phosphate can be adjusted by volume
weight to carry the treatment substance below the densest regions within the
body of water. The treatment substance can also include buoyant agents that
carry the nutrients from lower first regions to higher second regions after
the
treatment substance reaches the first region, which is typically below the
densest
regions. This buoyant agent can be biologically derived, chemically derived,
or
be a gas, such as one selected from, but not limited to, N2, CO, C02, H2, CH4,
SOZ, HzS.
In an alternative embodiment, the treatment substance comprises one or
more alcohols and a carbohydrate, which can be selected from the group of
whey, corn sirup, or hydrolyzed starch. In the alcohol and carbohydrate
mixture, the treatment substance has generally a 3:1 ratio of alcohol to
carbohydrate and can also include up to 30 mg. of total nitrogen per liter of
liquid to be treated. The microbe can be selected to include one or more
microbes selected of a genus coming from the group consisting of
Desulfovibrio, Desulfomonas, and Desulfomaculum.
In another alternative embodiment of the present invention, a process
for in situ immobilization of metals within soils located within a reservoir
is
disclosed that includes placing treatment substance and microbes within the
soil
prior to the addition of the water. Specifically, in the case where mines are
back-filled with water after they have been closed, the treatment substance,
whether dry or liquid, along with a microbe that generally produces microbial
sulfides, is places at various locations within the mine at various elevations
in
order to treat the mine for in situ immobilization upon filling of the mine
with
water. Once the treatment substance and microbes are in place, then water
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begins to flow within the reservoir, which wets the soil and the treatment
substance and the microbe. The microbes become active and feed upon the
microbial nutrients within the treatment substance to produce microbial
sulfides.
The microbial sulfides react in situ with metal ions or metal containing
compounds contained in the soil or otherwise soluble within the flowing water
to form metal sulfides. This reaction causes the metal ions or metal
containing
compounds to be reduced in solubility and eventually precipitate out as metals
sulfides into the soil or other earthen boundaries within the reservoir.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other features of the present invention will become
more fully apparent from the following description and appended claims, taken
in conjunction with the accompanying drawings. Understanding that these
drawings depict only typical embodiments of the invention and are, therefore,
not to be considered limiting of its scope, the invention will be described
and
explained with additional specificity and detail through the use of the
accompanying drawings in which:
FIG. 1 is a top view of a prior art mining area showing a mine
surrounded by a number of waste stacks and a pit lake.
FIG. 2 is a sectional side view of a pit lake affected zone being treated
according to a first embodiment of the invention. Treatment liquids are being
applied onto the surface of the pit lake.
FIG. 3 shows a sectional side view of a subterranean pit lake being
treated according to a second embodiment of the invention. Microbe nutrients
are being flowed into the lake as accessed via a chamber.
FIG. 4 shows a sectional side view of an abandoned mine prior to back
filling with liquid and that is being treated according to a third embodiment
of
the invention. Microbe nutrients are placed at various points within the mine
to
optimize treatment as the mine is filled with liquid.
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FIG. 5 shows a sectional side view of an open pit lake having various
strata of densification and being treated according to the present invention
to
account for the varying densities within the pit lake.
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DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
It will be readily understood that the components of the present
invention, as generally described and illustrated in the figures herein, could
be
arranged and designed in a wide variety of different configurations. Thus, the
following more detailed description of the embodiments of the system and
method of the present invention, as represented in Figures 2 through 5, is not
intended to limit the scope of the invention, as claimed, but is merely
representative of the embodiments of the invention.
The specific embodiments of the invention will be best understood by
reference to the drawings, wherein like parts are designated by like numerals
throughout.
FIGS. 2-5 illustrate selected forms of the present invention. These
forms of the invention are expected to apply to the following situation. A pit
lake 14 is provided over a subadjacent soil or other support earth materials
16.
A water soil interface 18 results from where pit lake 14 meets soil 16. Water
soil interface 18 extends along a base 20 of pit lake 14. One or more
water-soluble forms of one or more toxic metals, such as selected from the
group consisting of Pb, Hg, Cd, Fe, As, Se, U, Cu, Cr, Ni, Zn, Co, Mn, and Ag
exist within pit lake14 and may be rendered less mobile by the inventive
process
taught in accordance with the present invention. Such toxic metal contaminants
typically exist at relatively low concentration levels, 0.001-1000 parts per
million.
As shown in FIG. 2, a metal-containing boundary layer or boundary
zone 22 may also exist adjacent to pit lake 14. Metal-containing boundary zone
22 may exist if pit lake 14 is exposed to a waste stack or other tailings zone
that
has water leaching toxic metals out of the waste stack and past the water soil
interface 18, thereby forming metal containing boundary zone 22.
Pit lake 14, together with any present metal-containing boundary zone
22, defines a water soil affected zone 24. In accordance with the principles
of
the present invention, a method is disclosed that immobilizes the toxic metals
in
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situ within the water soil affected zone 24 to inhibit substantial migration
of
these toxic metals and prevent movement of contaminants into an extended area
26.
In one form, the method includes utilizing the biological activity of
5 microbes to generate sulfides in pit lake 14, which treatment extends
throughout
the water soil affected zone 24. The microbially-produced sulfides, which are
referred to herein as microbial sulfides, are combined with toxic metals in
the
affected zone to convert the metals into metal sulfides. In one exemplary
embodiment of the present invention, the microbially produced sulfides react
10 with metals or metal ions such as selected from the group consisting of Pb,
Hg,
Cd, Fe, As, U, Se, Cu, Cr, Ni, Zn, Co, Mn, and Ag. The toxic metals may be in
the form of metal ions, metal ion complexes, or metal containing compounds. A
possible mechanism for the conversion to metal sulfides, using the cadmium ion
as an example metal ion, is:
(1) C6 H12 06 + NAD + H+ 6COZ + 6H20 + NADH
(2) 10NADH + SO4 2- H2S + I ONAD + 4H20
(3) H2S(aqueous) + H20 H3O++ HS- (aqueous)
(4) HS- + H20 SZ- + H3O+
(5) CdZ++ (aqueous) + Sz- (aqueous) CdS (solid)
In the shown mechanism, NAD is nicotinamide adenine dinucleotide,
which is used ubiquitously in biological transport mechanisms.
Once metal sulfides, or other sulfided metallic forms, are formed, the
complexed metals become relatively insoluble in water and tend to precipitate
out of the water and into the boundary 24. The metals are thereby held in the
soil and boundary zone 24, preventing further water-borne migration.
It is believed that a variety of microbes that generate appreciable
quantities of sulfides can potentially be used in the treatment methods of the
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present invention. For example, microbes of the genera Desulfovibrio,
Desulfomonas and Desulfomaculum are known to generate appreciable
quantities of sulfides as a by-product of their growth and general biological
activity. They are believed to be suitable for use in the present invention.
Three
specific embodiments of the present invention will now be described in detail.
First Embodiment
As illustrated in FIG. 2, a first embodiment of the present invention
comprises treating an open body of water known as pit lake 14 to deliver a
treatment solution with sustaining nutrients on the surface of pit lake 14.
The
effective treatment of the pit lake 14 along with the water soil affected zone
24
requires a reasonable calculation of the volume of water found within pit lake
14
as well as the surface area of the water soil boundary area 20. Further still,
the
present invention requires a reasonable estimate of the amount of metal
contaminants within the affected zone 24 so that a reasonable calculation of
the
required microbial sulfide, with requisite nutrients, can be delivered to the
pit
lake 14 for treatment.
During the determination of the pit lake size and the boundary zone
size, the pH is measured in the water to determine if some areas are within a
pH
range of from about 3.0 to about 10. What is important is that there be a
potential biological activity zone wherein the microbial sulfides, along with
their
nutrients, can flourish for the immobilization of the water soluble metals
within
the affected zones.
Once the pH has been determined to be sufficient enough to provide a
biological activity zone, or the lake has been treated in such a way as to
provide
a temporary biological activity zone, a treatment liquid 30 is introduced onto
the
surface of pit lake 14. Typically, a source is provided from which treatment
liquid 30 is sprayed onto the surface of pit lake 14 and convection currents
along the surface distribute the liquid across the entire surface and within
the
varying depths of the water. The injection of the treatment liquid 30 can be
either mechanically delivered or gravity delivered.
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Treatment liquid 30 is primarily constituted of a suitable liquid base,
such as water. In addition to the water or other liquid base, there are a
number
of additional constituents within the liquid. Treatment liquid 30 also
includes at
least one microbe nutrient that is capable of sustaining biological activity
of at
least one microbe. Specifically, treatment liquid 30 will comprise an
appropriate nutrient supplement necessary for microbes.to grow within the
water
of open lake 14 as well as at the affected zone 24 and produce sulfides. Such
appropriate nutrient supplements are readily determinable by persons skilled
in
the art of microbial growth. Further, treatment liquid 30 should not contain
excess nutritional supplements beyond what is necessary for the microbes to
grow and produce sulfides. Such excess nutritional supplements would result in
economic waste, and potentially inhibit the anaerobic respiration necessary to
form sulfides. This form of inhibition is commonly known as fermentation.
The particular concentration of microbe nutrient varies depending upon
a pre-determined bio-availability of nutrients and the chosen speed of
biological
activity for the given application. The concentration of microbe nutrient also
depends upon the particular nutrient that is being employed. The concentration
of microbe nutrient also depends upon other aspects of the particular pit lake
14
and adjacent boundary areas 24 being treated. For example, the chemistry of a
particular boundary area 24 may be relatively less favorable or more favorable
to microbial conversion of the nutrient, which requires that the amounts used
are
adjusted to effect microbial growth and sulfide production to immobilize
metals.
An exemplary range of nutrient concentration is from about 0.1 to about 10
grams of nutrient per liter of liquid 30.
In one form of the invention, treatment liquid 30 includes a
carbohydrate microbe nutrient. Carbohydrate microbe nutrient is in the form of
either molasses, hydrolyzed potato starch, whey from milk or milk by-products,
and whey from milk or milk by-products with the protein fraction removed or
substantially removed.
In another form of the invention, treatment liquid 30 includes a
carbohydrate microbe nutrient. The microbe nutrient is typically selected from
one of the following types of nutrients, including molasses, hydrolyzed potato
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starch, whey from milk byproducts, and whey from milk byproducts with the
protein fraction removed or substantially removed. A list of microbe nutrients
includes alcohols, partially hydrolyzed amylosk or celldosis fractions,
aerosol
gelling components enabling treatment of a shallow lake or other temporarily
buoyant organic sawdust or straw. The treatment liquid 30 is delivered as a
treatment volume of generally 1 gram of treatment liquid for each liter of
liquid
to be treated. The alcohol and carbohydrates are mixed in a 3:1 ratio of
alcohols
to carbohydrates. About 30 milligrams of total nitrogen per liter to be
treated is
also added to the treatment liquid.
In an alternative embodiment of the present invention, treatment liquid
30 can include a carbohydrate microbe nutrient and a biologically suitable and
utilizable nitrogen source. The nitrogen source is included in amounts
sufficient
to provide concentrations within the treatment liquid from about 0 to about
500
milligrams per liter, or on a more constricted range from about 5 to about 100
milligrams per liter of N. Further, in this exemplary embodiment of the
invention, it is anticipated that the carbohydrate microbe nutrient includes
sugars and alcohols in a concentration of about 1 gram per liter total
carbohydrate and about 10 milligrams nitrogen per liter of liquid to be
treated.
In another alternative embodiment of the invention, treatment liquid 30
comprises a carbohydrate microbe nutrient, phosphate ions, and nitrogen
source.
Suitable sources of phosphate ions include sodium phosphate, potassium
phosphate, ammonium phosphate and potentially other phosphates. The
phosphate ion is included in sufficient amounts to provide concentrations in
the
treatment liquid from about 0.010 to about 0.25 grams per liter of liquid, or
contaminated lake water, to be treated, and up to 0.1 grams of total nitrogen
per
liter of fluid to be treated. Thus, the volume of liquid to be treated is
determined, the water is tested for contaminant types and concentrations for
each contaminant intended to be treated, then the amounts of nutrient,
phosphate
ions, and nitrogen source are each determined for addition to the lake
depending
upon the concentrations of contaminants.
In one specific embodiment of the present invention, the cysteine
content of the microbe nutrient will be low. Cysteine can interfere with
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microbial production of sulfides. Accordingly, the cysteine content in the
treatment liquid is kept low or is actually excluded from treatment liquid 30
so
as not to inhibit the production of microbial sulfides during treatment.
Treatment liquid 30 also comprises a pH to oppose the pH of the
surface of pit lake 14, relative to a neutral pH 7. Thus, if the surface of
lake 14
is alkaline, treatment liquid 30 is preferably acidic, also if the surface is
acidic,
treatment liquid 30 is alkaline. Treatment liquid 30 is buffered so as to
improve
formation of the temporary bio-activity zone of the treatment liquid within
lakel4.
Sulfide producing microbes are known to generally grow best in an
environment with a pH from about 4 to about 7. A region within soil water
boundary area 24 referred to herein as a biological activity zone. The pH and
buffer capacity of treatment liquid 30 is adjusted such that the interaction
of
boundary area 24 creates a biological activity zone within water and soil
boundary. Again, the method of this invention comprises providing at least one
sulfide-producing microbe capable of growing in the presence of treatment
liquid 30. The microbe may be provided before, after, or during the injection
of
treatment liquid 30, and is placed in proximity to the surface of pit lake 14
with
treatment liquid 30.
In one embodiment of the invention, the step of providing the sulfide-
producing microbe comprises treating the surface of pit lake 14 with at least
one
microbe. The microbe may be placed on the surface of pit lake 14 prior to,
subsequent to, or during the injection of liquid 30 onto the surface of pit
lake 14.
In an alternative embodiment of the invention, the step of providing the
sulfide-producing microbe comprises mixing the microbe with treatment liquid
and delivering the mixture onto the surface of pit lake 14 to begin the in
situ
immobilization of contaminating metals within pit lake 14.
In yet another alternative embodiment of the invention, the step of
providing the sulfide-producing microbe comprises utilizing microbes already
30 existing within pit lake 14 before liquid 30 is administered. The pre-
existence
of microbes within pit lake 14 may be due to human implantation, air-borne
dispersion, or natural conditions of the open pit lake 14.
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In accordance with the present invention, the method can also comprise
the step of administering one or more supplemental feedings of treatment
liquid
30 onto the surface of pit lake 14. The supplemental feedings are administered
after at least one prior treatment of treatment liquid 30, and is typically
provided
5 after the sulfide-producing microbes have begun growing. The supplemental
feedings are provided to sustain the growth of the sulfide-producing microbes.
The sulfide-producing microbes will produce sulfides over a longer period of
time when supplemental feedings are provided. Such long-term generation of
sulfides increase the immobilization of the metal ions, and minimize losses of
10 microbial nutrient due to fermentation. Since sulfides may eventually be
displaced from the coordination sphere of the metal ions through equilibrium
processes, the long-term generation of sulfides helps to insure that such
displaced sulfides are rapidly replaced or supplemented by other sulfides, as
in
the transition from pyrrhotite (Fel_,,S) to pyrite (FeS2) or marcasite.
15 Further, as an altemative to the use of a carrier liquid to deliver the
nutrients and microbes to the affected zone, solid materials that are not wet
or
liquid can be used instead. For example, the treatment substancc can be a
powder of nutrients that is activated simply =by contact with the water in the
pit
lake. This powder can be dispersed using air dispersal or air drop via
aircraft.
This is convenient also when the lake is too remote for pumping trucks to
access
for direct delivery at the shore. The treatment substance can also be less
refined
than a powder, either in pellet or clump form. The pellets can range in size
from
0.1 mm to 300 mm. It is understood that smaller sized pellets or powders
achieve a larger overall surface area that can react within the treated water.
The
larger sized pellets also serve as a time release mechanism as well since the
larger diameter pellets take longer to dissolve than the smaller pellets or
powder.
Additionally, the treatment substance when in liquid form can also be
dispersed
aerially via aircraft when border delivery is not possible.
Second Embodiment
Figure 3 illustrates a second embodiment of the present invention
where the body of water is actually a subterranean lake within the cavity of
an
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abandoned or existing mine. Subterranean lake 44 also includes an affected
soil
water boundary area 28 like that of FIG. 2. The water within subterranean lake
44 is treated using a water treatment composition 46. Treatment composition 46
permeates the water in lake 44. One or more delivery chambers 48 are formed
in the top surface of the soi152 above lake 44. These chambers 48 are placed
at
several locations to provide a uniform dispersion of treatment liquid 46
within
lake 44. These chambers are formed using conventional drilling techniques
known to those skilled in the art or are previously formed tunnels or shafts
formed during the mining operations. Natural caves and tunnels can also serve
as delivery channels for the treatment composition. Next, the treatment
composition 46 is then delivered into lake 44 either via mechanical feed or
gravity feed. The composition of treatment composition 46 is similar to that
of
treatment liquid 30 described above.
There are three types of subterranean lakes that need to be considered.
These lakes include a static lake, a sinking lake, and a gaining lake. The
static
lake has a constant volume that is either constant because of no inflow and
outflow, or is constant because there is a steady inflow meeting the same rate
of
outflow. In either event, the volume of the water stays relatively constant.
The
sinking lake is one where the outflow rate exceeds the inflow rate and is
draining at a given rate. The gaining lake is one where the inflow rate
exceeds
the outflow rate and therefore the volume continues to increase. It is
important
to know what type of lake is to be treated as it is important to attempt to
treat the
lake at the locations as close to the inflow sources as possible so that the
treatment composition can permeate throughout the water and affect the soil
boundaries within the water as thoroughly as possible. Should the treatment
composition be added in an outflowing region, then the treatment would occur
along the path traveled by the outflowing stream and not affect the general
body
of water upstream from the outflow region. Thus, placing treatment
composition nearest the inflow sources helps to distribute the treatment
composition within the body of water in a manner most effective in providing
in
situ immobilization.
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Thus, for gaining lakes, sinking lakes, and static lakes that have a
constant inflow and outflow, addition of treatment composition at the point of
input increases the chances of distributing the treatment composition
throughout
the water zones occupied in the abandoned mine. Accordingly, the chambers 48
are placed at locations as close as possible to the source of inflow into the
subterranean cavity.
In static bodies of water where there is no inflow or outflow, there is
little problem of contamination or a requirement that in situ immobilization
be
performed; however, in the event a breech occurs that allows the water to flow
out of the underground pit, treatment a priori prevents mobilization of
contaminate metals in accordance with the present invention. The process of
performing in situ immobilization within such bodies of water is also
accomplished within one or more embodiments of the present invention.
Specifically, the treatment composition 46 can be introduced within a static
body within a carrier agent that can generate a gas phase atmosphere of
nitrous
that carries the reducing agent within all parts of the chamber. Testing of
the
water sample is necessary in order to determine whether the water has reached
a
saturation level where nitrous would not diffuse within the water for one.
Thus,
it is contemplated that the treatment composition would be prepared in such a
manner as to have a density greater than that of the body of water to which it
is
introduced. This greater density allows the treatment composition to settle
near
the bottom or in other locations at points lowest areas to be treated such
that
during the gas phase transition, or the transition from a liquid or solid
composition into a gas-based carrying agent, the gas phase would introduce and
lift the reducing agent upward and outward.
The method of the present invention may further comprise a step of
providing one or more supplemental feedings of microbe nutrient into affected
zone 44 using one or more additions of pool treatment composition 46. The
supplemental feedings should be flowed onto the stack after at least one prior
feeding of microbe nutrient, and preferably after the sulfide-producing
microbes
have begun to grow. The supplemental feedings are provided to sustain the
growth of the sulfide-producing microbes. It is anticipated that the
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sulfide-producing microbes will produce sulfides over a longer period'of time
if
supplemental feedings are provided. As discussed previously, long term
generation of sulfides is advantageous for maximally immobilizing metal ions.
It is intended in the present invention that the treatment of the large
volume of water either in the open pit lake or in a subterranean pit lake that
the
microbial sulfides eventually interact with the soil boundary between the soil
and the water such that in situ immobilization of contaminant metals at such
soil
points is obtained. For example, as the microbial sulfides increase due to the
nutrients added, they filter throughout the water zone of the pit lake
neutralizing
soluble metals within the water. Further, they migrate towards the borders of
the
soil and are utilized to provide in situ immobilization of the water soluble
metals
located within the soils. Supplemental feedings encourage the growth of such
sulfide producing microbes such that within a short period of time, on the
order
of one to four months. The supplemental feedings are continued until test
samples of the water show a reduced level of contaminants, and that the soils
adjacent the water also show a greatly reduced level of contaminants being
treated.
Third Embodiment
Figure 4 illustrates a third embodiment contemplated within the present
invention. This particular embodiment relates to the anticipated filling of a
mine
to be closed. At this point, there is no water of significant volume within
the
mining cavity. It is recognized that the soil boundaries within the mine are
contaminated and it is useful to immobilize the heavy metals to prevent their
immobilization out of the mine and into adjacent water tables or soil
boundaries.
Further, it is desirable to treat the water that also carries the heavy metals
and
immobilize them as early as convenient as possible. Accordingly, as is
illustrated in Figure 4, an abandoned mine is illustrated.
Mine 100 has a cap head 102 located at an outer opening above a
surface opening of the mine. A main shaft 104 is illustrated penetrating from
a
top surface downward to a lowest horizontal shaft 106 that was used to
excavate
material from within the mine 100. Additional mining shafts in a horizontal
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plane are illustrated as shafts 108. Mine veins 110 are also illustrated that
typically provide a passage from open shaft 104 to the outer surface of the
mine.
These veins 110 typically are sealed to prevent seepage or leaking or
evacuation
of material from within the mine.
Since mine 100 is to be filled with water, treatment of the mine prior to
filling is done in accordance with the present invention. Specifically, mine
100
is treated by placing nutrients throughout the abandoned mine prior to filling
the
mine with liquid. The nutrients are consistent with those described above that
encourage the growth of sulfide producing microbes as defined and described
within the present invention. These locations are placed in the mine at
different
stages in advance of water penetration during the filling of the mine. For
example, a first nutrient 112 is located in excavation shaft 106.
Nutrients 112 are placed at the lowest level so that as the water, which
typically finds its lowest level during filling, will activate the nutrients
and the
microbes to begin the growth of the sulfide producing microbes to reduce the
metal contaminants for in situ immobilization. Additional nutrients and
microbes 112 are located at various other positions within the mine as
identified
at sites 116, 118, 120, and 122. Thus, as the water level rises, the water
reaching
a particular nutrient package activates the nutrient package to produce the
sulfide producing microbes. This enables the mine to be treated not only
incrementally as the water fills, but also completely as the soil boundaries
are
wetted and begin releasing the contaminated metals within the water.
Thus, it has been taught to treat a mine or cavity in advance of its filling
with water as a way of minimizing any metal mobilization within the soil
boundaries or the water.
Fourth Embodiment
The method for treatment of large bodies of water disclosed includes
the addition of biological or chemical reagents to a lake surface and
distributed
to various depths. The reagent dosage at depth is controlled by the several
parameters: reagent density, droplet size and miscibility. Large bodies of
water,
such as open pit lakes, are subject to the seasons with the various weather
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changes they bring. The lakes are subject to freezing during the winter and
warming well above freezing during the summer. These temperature extremes,
along with naturally occurring and varying wind forces, lead to stratification
of
the water into different density regions as shown in FIG. 5. In accordance
with
5 principles of the present invention, a method is disclosed to enhance the
distribution of reagents to perform a specific chemical transformation without
the need for further mechanical mixing regardless of the varying density
regions
found with a subject pit lake.
FIG. 5 illustrates a side view of a pit lake 14 having a depth D and an
10 immobilization boundary 22. Lake 14 has a maximum density region M, which
is determined by temperature sampling of the lake at varying depths. The
colder
the water, the denser the water becomes until 4 C. Thus, where the temperature
is noted to be approximately 4 degrees Celsius at level M, the maximum density
of the water is obtained. There may be varying levels of strata, but in this
15 example, the M level is the most dense. As such, the treatment composition
needs to be designed to penetrate this density level only, since it is the
maximum
density.
One example of the treatment composition utilized to perform in situ
immobilization of contaminant metals in accordance with the present invention
20 comprises in large part sugar syrup, which has a density of 11 lbs/gallon,
and
alcohol (methanol or ethanol), which has a density of 6.61bs/gallon. The sugar
syrup and alcohol are blended continuously by setting the flow rate of the
controlling constituent, in this example alcohol, and then modulating the flow
of
the densifying constituent in order to achieve a suitable density that exceeds
the
Maximum density of any strata level within lake 14. The densifying constituent
has a greater variance from the desired mean density, thereby controlling the
maximum or ultimate settling depth within the lake. In addition, both the
miscibility and the solubility of these constituents is varied to accomplish
the
same effect. Alternatively, the density needs only exceed the mean density of
the lake since the composition will itself have denser portions that reach
through
the densest strata levels of the lake.
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A deep pit lake, such as created in mining operations for copper, gold
or other minerals, is exposed to yearly freeze/thaw variation and moderate
fetch
(wind force) that stratifies the water into different thermally defined
layers. The
addition of a nutrient within the treatment composition to enable bio-
reduction
along a given electro-potential series to re-mineralize metallic species or to
remove other contaminants effectively treats only one layer of the lake since
it
poorly mixes with the other layers. Further it is likely to be unsuccessful in
meeting regulatory requirements due to re-oxidation (half reaction couple 1
and
2) before useful consumption in the desired half reaction couple 1 and 3:
Rxn 1: CH3OH + H20 = CO2 + 6H'+ 6e'
Rxn 2: 4H+ + O2 + 6e' = H20 1+2: Methanol + Oxygen = C02 and Water.
Rxn 3: SeO,Z' + 8H+ + 10e = Se + 4H20 1+3: Methanol + Selenate = C02 + Se
Since these reactions are biologically catalyzed, the addition of phosphate,
which has a density of 14.21bs/gallon, provides another degree of control of
delivery depth and enhance biological growth.
An alternative method of enhancing mixing is through biological or
chemical generation of a gas such as nitrogen from reduction of nitrates as in
coupling reaction 1 to reaction 4:
Rxn 4: 2N03 + 12H+ + 10e = NZ + H20.
Rising gas bubbles serve to carry excess settled sugars and reduced gases such
as sulfide toward the surface and react with reducible oxidized species along
the
way. This enables the treatment composition to extend to the water/soil or
earth
interface immobilization zone as described above to store reductive nutrients
for
future treatment of species mobilizing from the pit high walls as well as all
points between the zone and the surface of the lake.
The invention has been described in language more or less specific as
to structural and methodical features. It is to be understood, however, that
the
invention is not limited to the specific features shown and described, since
the
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means herein disclosed comprise preferred forms of putting the invention into
effect. The invention is, therefore, claimed in any of its forms or
modifications
within the proper scope of the appended claims appropriately interpreted in
accordance with the doctrine of equivalents.
