U.S. patent application number 10/789785 was filed with the patent office on 2004-09-02 for three-dimensional flow-through electrode and electrochemical cell.
Invention is credited to Larson, Arden L..
Application Number | 20040168909 10/789785 |
Document ID | / |
Family ID | 32962543 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040168909 |
Kind Code |
A1 |
Larson, Arden L. |
September 2, 2004 |
Three-dimensional flow-through electrode and electrochemical
cell
Abstract
A three-dimensional flow-through electrode includes an efficient
current feeding mechanism including current feeders comprising rods
of conductive material, such as graphite, which are inserted at
predetermined spacing into a flow-through electrode, such as a
block of graphite felt. The current feeders are appropriately
spaced throughout the electrode to allow for efficient current
distribution. The large surface area provided by the flow-through
electrode makes it possible to expose solutions or gases to
relatively large areas of electrical charges, instituting
electrical chemical reactions. A number of electrolytic chemical
processes using the electrolytic cells include water treatment,
chemical processing and production, hydro-metallurgical
applications, and environmental clean-up. A method to replace the
use of cyanide in gold and silver processing operations is also
provided.
Inventors: |
Larson, Arden L.; (Grand
Junction, CO) |
Correspondence
Address: |
SHERIDAN ROSS PC
1560 BROADWAY
SUITE 1200
DENVER
CO
80202
|
Family ID: |
32962543 |
Appl. No.: |
10/789785 |
Filed: |
February 27, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60450891 |
Feb 28, 2003 |
|
|
|
Current U.S.
Class: |
204/233 ;
204/275.1; 204/294 |
Current CPC
Class: |
C02F 2303/185 20130101;
Y02W 10/37 20150501; C25B 9/65 20210101; C02F 2001/4619 20130101;
C22B 11/04 20130101; C25C 7/02 20130101; C02F 1/46114 20130101;
C02F 1/4674 20130101; Y02P 10/20 20151101; C25B 11/031 20210101;
C22B 3/02 20130101; C22B 3/045 20130101; C02F 2001/46157
20130101 |
Class at
Publication: |
204/233 ;
204/294; 204/275.1 |
International
Class: |
C25B 011/12; C25B
009/00 |
Claims
What is claimed is:
1. An electrochemical cell, comprising: at least a first and a
second three-dimensional flow-through electrode, wherein said first
three-dimensional flow-through electrode is a positive electrode
and said second three-dimensional flow-through electrode is a
negative electrode; a current feeder associated with each of said
three-dimensional flow-through electrodes, wherein at least a
substantial portion of each of said current feeders is located
within said three-dimensional flow-through electrode associated
with said current feeder; a power supply coupled to each of said
current feeders to create an electrical potential therebetween; and
wherein the electrochemical cell is operable to facilitate a
chemical reaction on a feed solution which is flowing through said
electrodes.
2. An electrochemical cell, as claimed in claim 1, wherein at least
one of said three dimensional flow-through electrodes includes a
graphite felt material.
3. An electrochemical cell, as claimed in claim 2, wherein said
current feeder includes a plurality of graphite rods inserted at a
predetermined spacing into said graphite felt three-dimensional
flow-through electrode.
4. An electrochemical cell, as claimed in claim 3, wherein said
predetermined spacing is arranged according to the conductivity of
said feed solution and said electrical potential.
5. An electrochemical cell, as claimed in claim 2, wherein said
graphite felt material includes at least about 17,000 square feet
of graphite surface for each square foot of graphite felt.
6. An electrochemical cell, as claimed in claim 2, wherein said
current feeder is a conductive bar comprised on at least one of a
graphite rod, a copper rod, a steel rod, and a noble metal rod.
7. The electrochemical cell of claim 1, wherein said feed solution
is water and sodium chloride.
8. The electrochemical cell of claim 1, wherein said feed solution
is water and sodium bromide.
9. The electrochemical cell of claim 1, wherein said feed solution
is sea water.
10. The electrochemical cell of claim 1, wherein the feed solution
is untreated water.
11. A system for recovering a metal from an ore, comprising: a
reaction chamber containing ore; a first manifold operatively
associated with said reaction chamber operable to deliver a
leaching solution to a lower portion of said reaction chamber; a
second manifold operatively associated with said reaction chamber
operable to remove a pregnant solution from an upper portion of
said reaction chamber; and an electrochemical cell operatively
associated with said second manifold and operable to facilitate a
chemical reaction on said pregnant solution; wherein said leaching
solution is operable to leach a desired metal from said ore to
become said pregnant solution and said chemical reaction is
operable to remove at least a portion of said desired metal from
said pregnant solution.
12. The system for recovering a metal from an ore, as claimed in
claim 11, further comprising an ore bin chamber operatively
associated with said reaction chamber, and configured to deliver
said ore to said reaction chamber.
13. The system for recovering a metal from an ore, as claimed in
claim 12, further comprising: an ore delivery system operable to
deliver ore to said ore bin chamber; and an ore removal system
operable to remove leached ore from said reaction chamber.
14. The system for recovering a metal from an ore, as claimed in
claim 13, further comprising: a second ore bin chamber operatively
associated with said ore removal system, and oriented to deliver
said leached ore to a second reaction chamber; a third manifold
operatively associated with said second reaction chamber and
operable to deliver a second leaching solution to a lower portion
of said second reaction chamber; a fourth manifold operatively
associated with said second reaction chamber and operable to remove
a second pregnant solution from an upper portion of said second
reaction chamber; and a second electrochemical cell operatively
associated with said fourth manifold and operable to facilitate a
chemical reaction on said second pregnant solution; wherein said
second leaching solution is operable to leach a second desired
metal from said leached ore to become said second pregnant solution
and said chemical reaction is operable to remove at least a portion
of said second desired metal from said pregnant solution.
15. The system for recovering a metal from an ore, as claimed in
claim 11, wherein said electrochemical cell comprises: at least a
first and a second three-dimensional flow-through electrode,
wherein said first three-dimensional flow-through electrode is a
positive electrode and said second three-dimensional flow-through
electrode is a negative electrode; a current feeder associated with
each of said three-dimensional flow-through electrodes, wherein at
least a substantial portion of at least one of said current feeders
is located within said three-dimensional flow-through electrode
associated with said current feeder; and a power supply coupled to
each of said current feeders to create an electrical potential
therebetween.
16. The system for recovering a metal from an ore, as claimed in
claim 15, wherein said power supply comprises a direct current
supply operable to create about 9 volts of electrical potential
between said current feeders.
17. The system for recovering a metal from an ore, as claimed in
claim 15, wherein said first and second three dimensional
flow-through electrodes are about four inches by four inches, and
about one inch thick, and a flow rate of said pregnant solution
through said electrochemical cell is about 0.03 gallons per
minute.
18. A method for treating water, comprising: providing an
electrochemical cell having a first flow-through electrode and a
second flow though electrode, said first and second flow-through
electrodes spaced apart to provide an inter-electrode space;
applying a voltage between said first flow-through electrode and
said second flow-through electrode to create a positively charged
first flow-through electrode and a negatively charged second
flow-through electrode; feeding untreated water into said
inter-electrode space; and collecting treated water which has
passed through said second flow-through electrode.
19. The method for treating water, as claimed in claim 18, wherein
said first and second flow-through electrodes are graphite felt
electrodes and said applying a voltage step includes applying a
voltage to a current feeder associated with each electrode.
20. The method for treating water, as claimed in claim 18, wherein
said second flow-through electrode is a copper wire screen
electrode.
21. The method for treating water, as claimed in claim 18, wherein
said applying a voltage step includes: providing a DC power supply
having a positive terminal and a negative terminal; coupling said
positive terminal to said first flow-through electrode; and
coupling said negative terminal to said second flow-through
electrode.
22. The method for treating water, as claimed in claim 21, wherein
said DC power supply has a voltage potential of about 9 Volts.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of U.S. Provisional Patent
Application Serial No. 60/450,891 which was filed on Feb. 28, 2003,
entitled "THREE-DIMENSIONAL FLOW-THROUGH ELECTRODE AND
ELECTROCHEMICAL CELL." The entire disclosure of the provisional
application is considered to be part of the disclosure of the
accompanying application, and is hereby incorporated by reference
in its entirety.
TECHNICAL FIELD
[0002] The present invention relates to electrodes and, more
specifically, to the use of three-dimensional flow-through
electrode and electromechanical cells used for a number of
applications, including water purification, improving crop yields,
metal processing, chemical manufacturing and environmental
cleanup.
BACKGROUND OF THE INVENTION
[0003] Electrolytic processes are commonly conducted using planar
electrodes. Electrodes are well known in the art and include a
conductor which is in contact with a plate, in which various types
of solutions flow-by the electrode. A number of specific electrodes
have been designed in which the solutions flow-through one or more
electrodes. These electrodes have been made from a variety of
materials and material shapes. One problem addressed by the present
invention relates to the method of feeding electrical current into
an electrode; specifically into a three-dimensional electrode
composed of graphite felt material which provides a large surface
area for electro-chemical reactions.
[0004] Previously used graphite felt electrodes typically feed
electrical current through contact of a conductor metal either on
the edges of a thin graphite felt electrode, as disclosed, for
example, in U.S. Pat. No. 6,342,150 to Sale et al., issued on Jan.
24, 2002 and entitled "Redox water treatment system," and U.S. Pat.
No. 5,376,240 to Kaczur et al., issued on Dec. 27, 1994 and
entitled "Process for the removal of oxynitrogen species for
aqueous solutions," both of which are incorporated herein by
reference in their entirety. Other previously used graphite felt
electrodes feed current through a metal in planar contact with a
thin graphite felt electrode as disclosed, for example, in U.S.
Pat. No. 6,086,733 to Carey et al., issued on Jul. 11, 2000 and
entitled Electrochemical cell for metal recovery," or through a
metal back-plate in planar contact with a thicker graphite felt
electrode as disclosed in previously mentioned U.S. Pat. No.
5,376,240, both of which are incorporated herein by reference in
their entirety. Still other known graphite felt electrodes feed
current by inducing an electrical charge in a thicker graphite felt
electrode by inserting it between two oppositely charged electrodes
so the graphite felt becomes bi-polar with regard to electrical
charge. Such an electrode is disclosed in U.S. Pat. No. 5,744,028
to Goto et al., issued on Apr. 28, 1998 entitled "Water treating
apparatus," which is also incorporated herein by reference in its
entirety. All of these methods work to some degree for their
specific intended purpose; unfortunately, they all fail in their
ability to handle significant current flows.
[0005] Accordingly, it would be advantageous to have an electrode
which is relatively large, which can provide a large surface area
for efficient chemical reactions which can be used in water
purification, metal processing, chemical manufacturing and
environmental cleanup, to name a few possible applications.
Furthermore, it would be advantageous for such an electrode to be
capable of handling relatively large current flows.
SUMMARY OF THE INVENTION
[0006] The present invention solves the aforementioned problems and
meets the aforementioned needs, and other needs. In one embodiment,
an efficient method is provided for feeding current into a
three-dimensional, flow-through electrode preferably utilizing a
graphite felt material. Rods of a conducting material, preferably
graphite, are inserted at predetermined spacing into a block of
graphite felt electrode as current feeders. The spacing of these
conductor materials throughout the graphite felt block allows for
efficient current distribution despite the electrical resistance of
the graphite. The large surface area provided by the graphite felt
makes it possible to expose solutions or gases to electrical
charges instituting electrochemical reactions. This large surface
area, providing approximately 17,000 square feet of graphite
surface for each cubic foot of graphite felt, makes it possible to
perform electrochemical reactions on minute traces of elements in
solutions such as contaminants in water, and additionally makes it
possible for the mass transfer of electrons in chemical reactions
allowing for the high throughput of solutions in industrial
applications such as the production of chlorine from salt
water.
[0007] In one embodiment of the present invention, a flow-through
electrolytic cell is provided using the flow-through electrodes. A
number of methods of feeding solutions or gases into the
flow-through electrolytic cell are introduced depending upon the
direction of solution flow through the electrodes. Solutions or
gases can be either first oxidized in one electrode or reduced or
the solution can be fed between the electrodes so that one portion
flows through the oxidizing electrode while the other portion flows
through the reducing electrode. This methodology allows the
elimination of diaphragms in some electrolytic cells.
[0008] Specifically, one aspect of the present invention is an
electrochemical cell, comprising:
[0009] at least a first and a second three-dimensional flow-through
electrode wherein said first three-dimensional flow-through
electrode is a positive electrode and said second three-dimensional
flow-through electrode is a negative electrode;
[0010] a current feeder associated with each of said
three-dimensional flow-through electrodes, wherein at least a
substantial portion of each of said current feeders is located
within said three-dimensional flow-through electrode associated
with said current feeder;
[0011] a power supply coupled to each of said current feeders to
create an electrical potential therebetween; and
[0012] wherein the electrochemical cell is operable to facilitate a
chemical reaction on a feed solution which is flowing through said
electrodes.
[0013] Numerous electrochemical processes using these feeding
methods are disclosed. These processes include water treatment,
including the purification of contaminated water or the removal of
chlorine from drinking water. The processes further include a wide
variety of chemical processing, hydro-metallurgical applications,
and environmental clean-up, such as remediation of contaminated
soil. Further, a method to replace the use of cyanide in gold and
silver processing operations is disclosed as well as a method to
replace heap-leaching technology in general using a
counter-current, continuous-flow apparatus for ores. Thus, as
appreciated by one skilled in the art, the present invention has a
multitude of possible applications in numerous industrial and
commercial applications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a front perspective view of a basic flow-through
electrode in one embodiment of the present invention;
[0015] FIG. 2 is a front perspective view of a large flow-through
electrode in one embodiment of the present invention;
[0016] FIG. 3 is a front perspective view of a flow-through
electrode in another embodiment of the present invention;
[0017] FIG. 4 is a cross-sectional view of a flow-through
electrolytic cell according to one embodiment of the present
invention;
[0018] FIG. 5 is a cross-sectional view of a flow-through
electrolytic cell according to another embodiment of the present
invention;
[0019] FIG. 6 is a cross-sectional view of a flow-through
electrolytic cell according to another embodiment of the present
invention;
[0020] FIG. 7 is a cross-sectional view of a flow-through
electrolytic cell according to another embodiment of the present
invention;
[0021] FIG. 8 is a cross-sectional view of a flow-through
electrolytic cell according to another embodiment of the present
invention;
[0022] FIG. 9 is a flow chart diagram illustrating the operational
steps for one embodiment of the present invention;
[0023] FIG. 10 is a flow chart diagram illustrating the operational
steps of another embodiment of the present invention;
[0024] FIG. 11 is a flow chart diagram illustrating the operational
steps of another embodiment of the present invention;
[0025] FIG. 12 is a front elevation view of a mineral processing
apparatus of another embodiment of the present invention;
[0026] FIG. 13 is a front sectional schematic diagram showing the
layout of a series of E-VATs arranged in a train-like setting;
[0027] FIG. 14 is a plan view schematic which illustrates a
preferred embodiment of this invention for processing ores and
particularly ores containing gold;
[0028] FIG. 15 depicts a flow chart showing another embodiment of
this invention; a method of recovering metal, in particular, gold,
from ores requiring finer particle size preparation for liberation
of their mineral values;
[0029] FIG. 16 is a cross section of a typical in situ leaching
method for production of uranium from subterranean deposits using
another embodiment of this invention for regenerating oxidizing
lixiviants in a cost effective manner; and
[0030] FIG. 17 is a cross section illustration of in irrigation
treatment system of one embodiment of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0031] Referring now to the drawings, FIG. 1 illustrates one
embodiment of the present invention having a flow-through electrode
1 into which a current feeder 2 is inserted. The flow-through
electrode 1 can be any conducting material that is porous to the
flow of liquids or gases, and, in one embodiment, is graphite felt
such as that manufactured by National Specialty Products of
Fostoria, OH. The current feeder 2 can be any conductor material
capable of conducting an electrical current, and, in one
embodiment, is a graphite rod having a diameter of about
one-quarter inch or larger, and being capable of conducting a
current in the range of about 0.01 to 5.0 amperes. Other current
feeders may include, for example, copper, steel, or a noble metal
such as platinum, palladium, gold, as well as allows of metals such
as tantalum, tungsten, and titanium. The current feeder may also
separate base material which is plated with any of the previously
mentioned materials. The current feeder 2 is inserted into the
flow-through electrode 1 by boring a hole of lesser diameter than
the current feeder 2 in the flow-through electrode 1 such that when
the current feeder 2 is inserted, the fibers of the graphite felt
are in intimate contact with the current feeder 2, forming a good
electrical connection. A current feeder, as referred to herein, is
a device which facilitates the supply of electrical current to, or
the conduction of electrical current from, an associated electrode.
A number of other porous conducting materials could be used for the
electrode material such as, for example, steel wool, copper wool,
or wool composed of the noble metals such as platinum, palladium or
gold, as well as exotic alloys of metals such as tantalum, tungsten
and titanium. Graphite felt is utilized in one embodiment for this
invention because of its low cost when compared to most
alternatives, chemical resistance and its high hydrogen overvoltage
potential property.
[0032] FIG. 2 is a front perspective view of a flow-through
electrode 100 in one embodiment of the present invention which
includes a plurality of current feeders 2. An electrode of this
design containing one cubic foot of graphite felt would have a
surface area for electrochemical reactions of about 17,000 square
feet. This large surface area allows for relatively efficient
reactions to take place. These types of electrochemical reactions
are especially useful in numerous applications for removing trace
elements from solutions or gases, or the reduction and recovery of
valuable metals such as gold, silver, platinum and palladium. In
one embodiment, the flow-through electrode 150 is used to produce
electrodes for industrial applications requiring large current
flows. The flow-through electrode 100, in another embodiment is
used for a fuel cell electrode where the graphite felt is first
coated with a suitable catalyst. In such an application the current
feeders 2 are also used to remove electricity generated within the
electrode. The number and spacing of the current feeders 2 is
dependent upon the application and the amount of current required
for the application. For example, current of up to at least 50
amperes per square foot (600 amperes per cubic foot) is preferred
for chlorine production, while current of about 100 milliamps per
square foot is preferred for removal of trace elements from water.
The number, size, and spacing of the current feeders vary as
necessary for the desired current density. In one embodiment, the
current feeders 2, are covered by a polypropylene geotextile having
precut holes. This embodiment is useful when the current feeders 2,
have a relatively high voltage applied to them, which may act to
pull the carbon felt apart and cause a cell containing the
electrode to short-circuit.
[0033] FIG. 3 is a perspective view of an alternative method of
achieving electrical flow into a flow-through electrode 1 where a
conductive bar 104 is placed in intimate contact with up to four
sides of the flow-through electrode 1. This bar 104 can be any
conductive material, and in one embodiment is a graphite bar and
the flow-through electrode is graphite felt, similar to the
flow-through electrode depicted in FIG. 1. A drawback of this
method of feeding electrical current into flow-through electrode 1
is that as the dimensions of the flow-through electrode increases,
the resistance to electric current flow also increases due to the
resistance of the carbon felt. Accordingly, this design is most
advantageous in applications requiring relatively small current
flows in the range of about 5 milliamps per square foot up to one
ampere per square foot.
[0034] FIG. 4 is a cross-sectional front elevation view of a
flow-through electrolytic cell 108 using the basic electrode
described in FIG. 1, where two such flow-through electrodes 1 and
1a, with current feeders 2 and 2a, are placed in a container 3 made
from inert material, such as a variety of plastics including PVC,
HDPE, Acrylic, or any other suitable material that is not a
conductor of electricity and is not chemically reactive with any of
the gases or liquids used in the electrolytic cell 108. Such
containers may be either open-top or totally enclosed, depending on
the application. The flow-through electrodes 1 and la separate the
electrolytic cell 108 into three specific chambers 4, 5, 6. As
appreciated by one skilled in the art, any possible number of
geometric configurations may be utilized depending on the
application, and including other chambers when a plurality of
electrodes are put into series and also using combinations of cells
including series, parallel, and cascade configurations. In this
embodiment, a solution, or gas, enters the flow-through
electrolytic cell 108 from stream 7 (under sufficient hydraulic
pressure to induce flow) through a valve (not shown) into chamber 4
where it passes through a negatively-charged electrode la into
chamber 5 and then through a positively-charged electrode 1 and
into chamber 6 where the product stream 8 exits through an exit
valve (not shown). Both the current feeders 2, 2a are connected to
a direct current power supply (not shown). In this unit a direct
electrical current is applied through current feeder 2 into
positive electrode 1 and negative electrode 1a and into current
feeder 2a to complete the circuit. The amount of current and
voltage is dependent upon solution composition and desired
results.
[0035] One application for a flow-through electrode 108 of this
embodiment includes stream 7 which is composed of a solution of
water and sodium chloride. In the negative electrode 1a, under
sufficient voltage of at least about 3 volts, and, more preferably
about 5-10 volts, some of the water is electrolytically separated
into hydrogen gas and hydroxide ions. The hydrogen gas is vented
from chambers 4 and 5 (not shown), while the solution, with its
increased hydroxide ion level passes into chamber 5 and then
through the positive flow-through electrode 1 where some of the
chloride ions are oxidized to free chlorine which immediately
reacts with the hydroxide to form a hypochlorite ion within the
flow-through electrode 1 and within chamber 6 so that the product
leaving the flow-through electrolytic cell is a solution of water,
sodium chloride and sodium hypochlorite (a common chemical used as
household bleach, swimming pool disinfectant and numerous
industrial processes).
[0036] FIG. 5 is similar to FIG. 4 as to the design and
construction of the flow-through electrolytic cell. The primary
distinction is in the direction of flow of solutions or gases to be
processed. In this embodiment, solutions or gases to be processed
in the flow stream 9 are introduced into chamber 5 through a valve
(not shown) where a portion of the solution passes through a
negative electrode 1a and the remainder of the solution passes
through the positive electrode 1. In this unit a direct electrical
current is applied through current feeders 2, 2a into positive
electrode 1 and negative electrode 1a, the amount of current and
voltage is dependant upon solution composition and desired results.
Thus through an electrolytic process, stream 9 is separated into
two different products, including stream 7 and stream 8.
[0037] As an example of this embodiment, a solution of sodium
chloride and water is fed into chamber 5 as stream 9. A portion of
the solution passes through the negative flow-through electrode 1a
into chamber 4 and the remaining portion of solution passes through
the positive electrode 1 into chamber 6. The amount of each product
stream 7 and 8 is regulated by a valve (not shown) on chambers 4
and 6. In the negative electrode 1a water is electrolytically
separated into hydrogen gas and into hydroxide ions while in the
positive flow-through electrode 1 the chloride ion is oxidized to
chlorine gas which dissolves into water to form hypochlorous acid.
Thus the solution in chamber 4 is enriched in sodium hydroxide
while the solution in chamber 6 is enriched in hypochlorous acid.
The pH of the solution in chamber 4 is substantially basic while
that of the solution in chamber 6 is substantially acidic. The
inventor has conducted tests where the pH in chamber 4 reached in
excess of pH 13, while the pH of chamber 6 was as low as 1. These
results can be varied by controlling the voltage to the electrodes,
the solution flow rate through each electrode and the composition
of the original solution. For example, in one test, a voltage of 9
volts, with a starting solution of 2 percent sodium chloride was
used, resulting in a flow rate of 70 ml/min for each electrode, and
each electrode was 4 inches by 4 inches by 1 inch thick. The
resulting solution in chamber 6 had a pH of 3.8 and an ORP of 1,045
millivolts, and a solution in chamber 4 had a pH of 11.7 with an
ORP of 37 millivolts.
[0038] It will be obvious to one skilled in the art that this is a
fundamental electrochemical cell with the ability to separate any
salts into their original acidic and basic components. It will also
be obvious to one skilled in the art that this embodiment allows
electrochemical processes to be conducted without the use of a
diaphragm to separate anode and cathode products. The flow-through
nature of the electrodes 1a and 1 used within substantially
prevents the back-flow of products due to the fact that electrical
charge on the flow-through electrodes 1a and 1 repels ions or
products with the same charge. For example, the hydroxide ion
produced in the negative electrode 1a will not flow from chamber 4
into chamber 5 because it would have to traverse the thickness of
the negative electrode 1a that has a repelling charge.
[0039] FIG. 6 is similar to FIG. 4 in the construction of the
flow-through electrolytic cell. The primary distinction is that the
solutions or gases to be processed, as depicted as stream 11, first
enter chamber 6 where they first flow through the positive
electrode 1, then into chamber 5 where they flow through the
negative electrode 1a into chamber 4 and exit as product stream 10.
In this specific embodiment, a direct electrical current is applied
through current feeders 2, 2a into positive electrode 1 and
negative electrode 1a, the amount of current and voltage is
dependant upon solution composition and desired results.
[0040] One specific application of this embodiment is in the
treatment of contaminated water to is provide water suitable for
human consumption. Untreated water, with sediments removed, is
processed as depicted in stream 11 where it enters chamber 6 and
passes through the positively charged flow-through electrode 1.
Within this electrode, some existing chloride ions (which are
common to all natural water) are oxidized to chlorine and
micro-organisms are subjected to an electric current. Both the
electric current and the chlorine act to kill substantially all of
the disease-causing micro-organisms. Trace organic harmful
compounds are oxidized as well. The oxidized solution flows into
chamber 5 and then through the negative electrode 1a where the
chlorine produced within the positive electrode is reduced back to
chloride and transition metals present in the original untreated
water are electro-deposited within the negative flow-through
electrode 1a. The resulting solution in chamber 4 and exiting as
stream 10 is potable water. The current and voltages necessary for
this embodiment can readily be produced by an inexpensive solar
cell, which produces at least about 1.7 amp, 9 volts, and 15 watts.
Most any other means of electricity generation, such as wind power
or a small hydroelectric generator could also readily produce the
current and voltages necessary for this embodiment. Voltage is the
most important factor and is preferably at least about 3 volts. It
is contemplated that this embodiment may have widespread usage
worldwide to provide potable water in remote locations not in
proximity to a power grid.
[0041] FIG. 7 is similar to FIG. 6 with the addition of the option
of removing a stream 12 from the inter-electrode chamber 5 through
a valve (not shown). This embodiment allows the removal of an
additional product. For example, using the water purification
example of FIG. 5, a stream 12 could be removed from chamber 5 that
has a high Oxidation-Reduction Potential (ORP) due to the chlorine
produced within the positive electrode. Such a stream is useful in
cleaning households and household items. In testing, this stream
has had a measured ORP of between +600 millivolts to +1100
millivolts. Thus, this embodiment allows the treatment of raw water
to produce both drinkable water and a solution useful in cleaning
unsanitary conditions, utensils, or any other items.
[0042] FIG. 8 is similar to FIG. 4 with the addition of stream 12
removed from the inter-electrode chamber 5 through a valve (not
shown). This embodiment allows the production of two products from
a process stream 10. One example of this embodiment would be the
processing of a solution of water and sodium chloride entering
chamber 4 as process stream 10, where it first passes through the
negative flow-through electrode 1a. In one embodiment, a direct
electrical current is applied through current feeders 2, 2a into
positive electrode 1 and negative electrode 1a, the amount of
current and voltage is dependant upon solution composition and
desired results. More specifically, this application may be used to
produce sodium hypochlorite from low concentration salt solutions.
An optional circulating loop 13 of solution raises the pH of the
product in chamber 5 to the point where it will dissolve all of the
chlorine produced in electrode 1. The production of chlorine from
low salt solutions is generally hampered by the competing
production of oxygen at the electrode. As will be understood, this
embodiment may have important usage in other electrochemical
processes.
[0043] In electrode 1a, water is electrolytically separated into
hydrogen gas and hydroxide ions. The hydrogen gas may be removed
from chambers 4 and 5 through valves (not shown) while the
hydroxide ion enriched solution passes into chamber 5 where a
portion of it may be withdrawn through process stream 12 for
further usage, including recycling it back to process stream 10 by
process stream 13 in order to increase the strength of the incoming
solution 10 in hydroxide ions. In this embodiment, the
concentration of hydroxide ions in input stream 10 can be increased
by the recycling the solution from chamber 5. The solution moving
through the positive flow-through electrode 1 is thus more
concentrated in hydroxide ions. The chlorine produced in the
positive flow-through electrode 1 reacts with the hydroxide ions to
form hypochlorite with the resulting solution in chamber 6 and
represented by product stream 11, which in this example is a
solution of sodium hypochlorite, a commonly used industrial
compound. Thus, in this embodiment, a solution process stream 10 of
water and sodium chloride can be separated into three products,
hydrogen gas, sodium hydroxide and sodium hypochlorite.
[0044] FIG. 9 illustrates another embodiment of the present
invention. It is a generalized flow diagram of a process to treat
industrial waste water containing cyanide and metals in solution.
One such source of this type of metal laden solution is, for
example, from electroplating operations. Another source is from
mining operations, such as gold and silver heap leaching operations
such as the one at the Florida Canyon Mine located in Humboldt
County, Nevada. In this embodiment, a source solution 20 containing
a cyanide and dissolved metals is pumped into a closed mixing tank
22 through process line 24. In the mixing tank 22 an oxidizing
solution containing chlorine and oxygen from process line 8 is
mixed with the source solution 20. In this mixing tank 22, the
chlorine and oxygen destroy the cyanide by oxidizing it to nitrogen
and carbon dioxide. Also oxidized are metals in a reduced state
such as ferrous iron and arsenic compounds. This oxidized solution
leaves the mixing tank 22 through process line 10 where it enters
the inner-electrode chamber 5 of the flow-through electrolytic cell
3. In this unit, a direct electrical current is applied through
current feeders 2, 2a into positive electrode 1 and negative
electrode 1a. The natural amount of current and voltage applied to
electrodes 1, 1a is dependant upon solution composition and desired
results. More specifically, the voltage must be high enough to
produce either chlorine or oxygen or both, and in one embodiment is
above about 3 volts. The current is dependent upon the
concentration of the dissolved salts, a salt solution of 500 ppm or
more would draw a much larger current than a solution with only 50
ppm dissolved salts.
[0045] A portion of the solution passes through the positive
charged three-dimensional flow-through electrode 1, in which
chloride ions present in the original solution are oxidized to
chlorine and some water molecules are oxidized to produce oxygen.
This oxidizing solution passes from the flow-through electrode 1
into chamber 4 of the flow-through electrolytic cell 3 and then
into process line 8 through a regulating valve (not shown). The
remaining solution in chamber 5 passes through flow-through
electrode 1a which, in this embodiment, is made of a wire mesh of a
conducting material such as copper, lead, or stainless steel. This
electrode 1a has sufficient openings to allow passage of
precipitated metals and metal compounds. The electro-chemical
reactions occurring in and around this electrode are of a reducing
nature such that some metals are electro-deposited on the wire mesh
while water is reduced to produce hydrogen and hydroxide ions. Some
metals precipitate as hydroxides, others as oxides and some are
further reduced by the action of the dissolved and entrained
hydrogen in chamber 6. As will be understood by one trained in the
art, the electro-chemical reactions in, at, and around electrode 1a
will depend upon metal concentration, applied voltage, current
flow, solution flow rate and solution composition. Indeed, when
using a solution with 5000 parts per million sodium chloride and
when this electrode is operated at a voltage in the range of 4 to 9
volts and a current density of 50 amperes per square foot, the
solution passing through this electrode 1a virtually boils with
hydrogen gas bubbles and has an Oxidation-Reduction Potential of
minus 1000 millivolts or lower. This reduced solution leaves
chamber 6 through process line 7 and may be stored in a treated
solution tank 26.
[0046] Another embodiment of the present invention is used in an
agricultural setting. In this embodiment, water used for irrigation
of plants is generated by an electrolytic cell of the present
invention. The electrolytic cell includes a negatively charged
electrode of copper wire screen and a positively charged electrode
of graphite felt. The copper wire screen electrode of this
embodiment allows irrigation water to pass through without removing
substantial amounts of transported nutrients. Standard irrigation
water is fed into the inter-electrode spacing and most of it,
approximately ninety percent in one embodiment, is allowed to pass
through the negatively charged copper wire screen electrode and
collected in an inert tank. The water passing through the
positively-charged electrode is discarded in one embodiment. The
cell of this embodiment is operated at a direct current of about 9
volts and approximately 3 to 5 amperes of current. Each electrode
was 12 inches square and one inch thick. The water produced through
the negative electrode has an oxidation-reduction potential of
approximately -300 to -600 millivolts. This is by definition, an
anti-oxidant water, as it donates electrons to reduce oxidants and
free-radicals. This water is then taken from the inert tank and
used as irrigation water.
[0047] In one example of the irrigation embodiment, a test garden
was planted by the inventor. The garden was divided into two
substantially identical sides. One side was irrigated with water
directly from a pond while the other side was irrigated with pond
water that had passed through the above-described electrolytic
cell. Two tanks of 300 gallons capacity were filled for each
irrigation event, normally three days apart. One tank was filled
with the raw pond water, while the other tank was filled with
hydrogen-rich water generated by the flow-through electrolytic
cell.
[0048] A variety of vegetables were planted and notes were taken on
a daily basis. It was observed that the vegetables irrigated with
the hydrogen-rich water germinated faster and grew slightly faster
compared to the vegetables irrigated with untreated water. In
general, the portion irrigated with the hydrogen-rich water looked
healthier. No insecticides or fertilizers were used. Later in the
summer, problems were encountered with the irrigation lines
plugging with algae from the pond water. This led to a less than
ideal watering situation. It was noted that the side irrigated with
the hydrogen-rich water exhibited little sign of wilting when
without water for several days while the other side of the garden
showed moderate to severe heat stress when without water for
several days. In the fall, a test plot of carrots from each side of
the garden was dug. All of the carrots in each plot were extracted,
cleaned, had their tops cut off, and weighed. It was observed that
the average carrot irrigated with hydrogen-rich water was 49
percent heavier and larger than those that were irrigated with the
raw pond water.
[0049] Another example involves numerous other flow-through
electrolytic cells which have been constructed and tested using tap
water as a source using the scheme depicted in FIG. 5. The tap
water was fed into the inter-electrode space and allowed to flow
through each side of the electrolytic cell without restriction.
Approximately forty percent of the water passed through the
negatively-charged electrode while approximately sixty percent of
the water passed through the positively-charged electrode. The
electrodes were connected to a direct current power supply with a 9
volt potential. The cells drew an average of 1 ampere per square
foot of electrode. When the feed tap water had an ORP of about +450
millivolts due to dissolved chlorine, the water that passed through
the negative electrode had an ORP of about -100 millivolts while
the water that passed through the positive electrode had and ORP of
about +550 to +600 millivolts. Tiny bubbles of hydrogen could be
observed in the water that passed through the negative
electrode.
[0050] In one test, an equal volume of this hydrogen-rich water was
mixed with an equal volume of tap water and an ORP calumel
reference probe was inserted. The ORP of the mixture dropped from
the about +450 millivolts of the tap water to about +100 millivolts
of the mixture within about two minutes. This is a demonstration of
the anti-oxidant nature of the hydrogen-rich water. The
hydrogen-rich water had the effect of neutralizing the chlorine (a
free radical oxidant) in the water mixture. Furthermore, a taste
test demonstrated no chlorine taste.
[0051] FIG. 10 illustrates another embodiment of the present
invention. In this embodiment, the solution source 30 is a liquid
containing dissolved metals including, but not limited to, gold,
silver, copper, lead and zinc, but does not contain cyanide. Such a
solution could originate from many industrial processes, such as,
for example, metal plating, ore processing or scrap recycling, and
would most likely be acidic. The solution could also be from
polluted sources such as acid mine drainage. This solution may
contain chlorides, nitrates, sulfates or phosphates. In this
embodiment, solution 30 flows through process line 34 to mixing
tank 32 where it is mixed with a reducing alkaline solution from
chamber 6 in the flow-through electrolytic cell 3 which flows
through process line 7 to the mixing tank 32. In the mixing tank 32
two types of reactions occur, wherein one is a reducing reaction of
the metals to metal powder by the action of hydrogen produced
within the electrode 1a by the electrolytic reduction of water.
This also produces an increase in the hydroxide ion content of the
solutions which may cause a second reaction to simultaneously occur
including the precipitation of metal hydroxides. As will be
understood by one skilled in the art, the chemical reactions may
potentially remove virtually all metals in the solution due to the
low solubility of metal hydroxides in reducing alkaline water. One
skilled in the art will also recognize that the chemical processes
occurring in mixing tank 32 can be drawn out into individual
reactions in separate mixing tanks by first separating the hydrogen
gas in process stream 7 from the hydroxide rich liquid so that the
original solution can have its pH raised in increments by addition
of hydroxide rich liquid separated from process stream 7 to allow
individual metal hydroxides to precipitate. The Oxidation-Reduction
Potential of the process stream 34 could also be regulated with the
addition of controlled amounts of the separated hydrogen gas, thus
sequentially reducing dissolved metals according to their
respective oxidation-reduction potentials.
[0052] The reduced alkaline solution from mixing tank 32 flows
through process line 34 into filter 36 where solids 38 containing
metal powders, metal oxide powders and/or metal hydroxides are
removed for environmentally safe disposal or metal recovery. The
resulting metal-free liquid from the filter 36 flows through
process line 10 into chamber 5 of flow-through electrolytic cell 3.
In this unit a direct electrical current is applied through current
feeders 2, 2a into positive electrode 1 and negative electrode 1a.
The amount of current and voltage is dependant upon solution
composition and desired results. Part of the solution flows through
negative electrode 1a where hydrogen gas and hydroxide ions are
produced for the recycled solution in process line 7, while the
remainder of the solution in chamber 5 flows through positive
electrode 1 where the hydroxide ions are neutralized by the
electrolytic oxidation of water which can reduce the pH level to 7
which is neutral. Thus the solutions leaving chamber 4 through
process stream 8 is a substantially metal-free, clean solution
which may be stored in treated solution tank 40.
[0053] FIG. 11 illustrates another embodiment of this invention
which generally depicts a process diagram for recovering metals
from ores, including, but not limited to gold, silver, copper,
lead, zinc, tin, cobalt, platinum and palladium. In this
embodiment, crushed ore 50 is conveyed by conveyor 54 into device
56, herein called the E-VAT, which is a continuous flow,
counter-current leaching system. Lixivating solution 8 such as a
solution of 1/10% to 30% sodium chloride and 0% to 15% sodium
bromide, is added to the ore in the E-VAT 56 after first passing
through the electrode 1 where it is oxidized to produce sufficient
chlorine, bromine or compounds of both so that it dissolves the
targeted metal contained within the ore resulting in a pregnant
solution which leaves the E-VAT 56 through process line 58. At the
same time, leached ore is transported through rinsing mechanism 60
where fresh water from process line 62 is added to displace
entrained liquids in the leached ore so that a rinsed and leached
ore 64 is produced for further environmentally safe disposal. The
fresh water 62 is derived from a portion of lixiviant solution in
process line 8 through a salt/water separator 66 using reverse
osmosis, electro-dialysis or another effective method to produce
fresh water from salt water. The waste solution 68 from the
salt/water separator 66 is added back to the lixiviant solution in
line 8 through process line 70. The pregnant solution containing
the targeted metals flows through process line 58 into mixing tank
72, where a solution coming from chamber 6 of flow-through
electrolytic cell 3 is added through process line 7. In this mixing
tank 72, at least two chemical reactions occur, the first being the
reduction of metals by hydrogen gas entrained in the solution from
process line 7, and the second reaction being the precipitation of
metal hydroxides and oxides by the hydroxide ions in the solution
from process line 7. It will be understood by one skilled in the
art as to which type of these reactions occur depends upon the
metals present, their concentration, the pH and Eh of the pregnant
solution.
[0054] The precipitated solution leaves mixing tank 72 through
process line 74 where it passes into filter 76 where the
precipitated metals and metal compounds are removed as filter cake
78 which can be mixed with fluxes such as borax, sodium carbonate,
fluorite, silica, and lime, and melted to produce metal bullion, if
desired. The barren solution filtrate from the filter 76 leaves
through process line 10 where it enters chamber 5, the
inter-electrode chamber, of flow-through electrolytic cell 3. In
this unit a direct electrical current is applied through current
feeders 2, 2a into positive electrode 1 and negative electrode 1a,
the amount of current and voltage is dependant upon solution
composition and desired results. In one embodiment, the flow rate
through process line 10 is about 100 mL/min and the flow-through
electrodes 1, 1a are each about 4 inches per side and one inch
thick. It will be understood that flow rates may vary based on the
size of the electrodes, the current and voltage, and the solution
being fed into the electrolytic cell.
[0055] A portion of the barren solution passes through flow-through
electrode 1a where water is separated into hydrogen gas and
hydroxide ions and enters chamber 6 where it is recycled to mixing
tank 72 for metal precipitation. The remaining barren solution
passes through flow-through electrode 1 where it is oxidized by the
electrolytic process so that any chloride or bromide ions are
oxidized to chlorine and bromine and their compounds which dissolve
in the solution in chamber 4 to form hypochlorous acid or
hydrobromous acid, dependant upon solution chemistry. The pH of
this solution may also be lowered by the oxidation of water to
produce oxygen and hydrogen ions. This solution is now the
lixiviant which flows through process line 8 back to the E-VAT
leaching system. Thus, this embodiment of the invention is a closed
system to recover metals from their ores, waste materials or scrap
using the flow-through electrodes 1 in a flow-through electrolytic
cell.
[0056] An example of the embodiment is now described. Gold ores
have been tested using a system of this embodiment, resulting in a
recovery of contained gold which was over eighty-two percent in an
ore containing 5 grams of gold per ton, in four hours of leaching
time. This is approximately twenty times faster than conventional
leaching techniques which require leaching the gold with cyanide.
The lixiviant used in one embodiment is a solution of water and
sodium chloride, with and without sodium bromide. Thus, this
embodiment can replace the usage of cyanide for such leaching
applications which is currently used world-wide, with occasional
horrific environmental consequences. Table 1 contains results from
one test of a system of this embodiment.
1TABLE 1 STEALTH LEACH TEST Sample Gold Soln Wt. Ore Wt. Gold Rec
Time Designation PPM gms 200 Ratio ppm % Rec Cum Rec minutes Hours
ST-1 1.02 85 200 0.425 0.43 7.55% 7.55% 25 0.42 ST-2 1.56 145 200
0.725 1.13 19.71% 27.27% 85 1.42 ST-3 1.23 2.89 200 1.445 1.78
30.98% 58.24% 145 2.42 ST-4 0.93 304 200 1.52 1.41 24.64% 82.88%
205 3.42 ST-5 0.14 4.36 200 2.18 0.34 5.32% 88.20% 445 7.42 ST-6
0.05 5.0 200 2.65 0.13 2.31% 90.50% 1440 24.00 5.19 90.50% 0.151
0z/tn 90.50% recovered 0.548 0.016 Tails assay 9.50% tails 5.738
0.167 head grade 100.00%
[0057] FIG. 12 is a sectional, front elevation view of one
embodiment of the continuous-flow counter-current leaching system,
referred to as the E-VAT, of FIG. 11. In this system, two round
cone-bottomed tanks 150 and 154, made from rotary molded hi-density
polyethylene or other suitable material are positioned vertically
above each other and supported by a structural steel silo 158. The
tanks are connected by a feed tube 162 through which crushed ore
166 stored in tank 150, used as an ore bin passes into tank 154,
used as a leaching reactor, where the ore is contacted with a
lixiviant solution which enters through pipe 170. The lixiviant
solution 172 flows up through the crushed ore in tank 154 where it
dissolves the desired elements and becomes pregnant solution 174,
which exits through pipe 178 (equivalent to process line 11 of FIG.
11). The crushed ore flows down through tank 154 (the leaching
reactor) by gravity where it flows through outlet pipe 182 into
auger 186. It moves up auger 186, powered by variable speed motor
drive mechanism 190. Fresh water is injected into the auger through
pipe 194 where it displaces entrained solutions. The fresh water is
injected at a point above the liquid level 198 in tank 154 (the
leaching reactor) so that the fresh water flows down the auger by
gravity. The leached and rinsed ore then exits the auger 186
through discharge pipe 202 where it falls to the ground as pile 206
for further environmentally safe disposal. The auger 186 is fitted
with a clean-out plug 210 and drain pipe 214.
[0058] In this system, the crushed ore flows by gravity down
through the leaching reactor 154 while the lixiviant flows up
through the ore. The strongest solution therefore contacts the
weakest (lowest metal content) ore which is the ideal metallurgical
condition to maximize metal recovery and minimize reagent
consumption. The flow rate of ore through the E-VAT is easily
regulated by adjusting the speed of the auger through the variable
speed motor drive mechanism 190. The solution flow rate, and thus
the residence time, in the leaching reactor is readily regulated by
the injection rate of the solution.
[0059] FIG. 13 is a front sectional schematic diagram showing the
layout of a series of E-VATs arranged in a train-like setting. Only
major components are depicted. In this embodiment, crushed ore is
fed into ore hopper 301 where it is conveyed via auger 302 into ore
hopper 303. The ore flows by gravity down through E-VAT unit 304,
is conveyed via auger 305 into E-VAT unit 306, where it flows by
gravity into auger 307 which conveys it into E-VAT unit 308 where
it flows by gravity into auger 309 which conveys it into E-VAT unit
310 where it flows by gravity into auger 311 which conveys it into
E-VAT unit 312 where it flows by gravity into auger 313 where it is
conveyed for disposal. In this embodiment, the ore can flow either
continuously, or in batches, depending upon the processing needs.
Lixiviants are injected into the bottom of each E-VAT unit and
removed from the upper portion of the same unit as depicted more
fully in FIG. 12.
[0060] FIG. 14 is a plan view schematic which illustrates an
embodiment of this invention for processing ores and particularly
ores containing gold. In this embodiment, crushed ore is placed 5
into ore hopper 401. The fineness of crushing is dependent upon the
particular leaching requirements of the ore. The ore enters an
auger 403 where it is conveyed into E-VAT unit 404. At a point
shortly after entering the auger 403, an agglomerating agent such
as Portland cement, long-chained polymers, flocculates or other
suitable binding agent is added from tank 402. The addition of the
agglomerating agent coupled with the rotary action of the auger 403
while conveying the ore has the effect of agglomerating the ore by
attaching fine particles to larger ones. The auger 403 can also be
discharged into an ore bin vertically above E-VAT 404 as depicted
by 303 in FIG. 13. This ore bin can be sized to allow curing time
for the agglomerating agent, or if necessary, an additional E-VAT
unit without any liquid additions can be used at this point in the
process for longer curing times. In E-VAT unit 404 a lixivating
agent is injected into the bottom of the unit where it percolates
up through the crushed and agglomerated ore reacting with, and
dissolving metals. This metal-laden pregnant solution flows from
the upper portion of the E-VAT unit 404 into pregnant storage tank
414. The pregnant solution is then pumped through flow-through
electrolytic cell 419 as depicted in FIG. 4. The contained metals
of the pregnant solution are deposited in the negatively-charged
flow-through electrode. The lixiviant is restored when it passes
through the positively-charged flow-through electrode. The restored
and regenerated lixiviant flows into storage tank 423 from which it
is then pumped back into E-VAT unit 404, this forming a completed
closed circuit of solution flow.
[0061] From E-VAT unit 404 the partially leached ore passes into
transfer auger 405 where it is conveyed into E-VAT unit 406 where
the leaching cycle is repeated as described above for E-VAT unit
404. These steps are repeated in E-VAT units 408, 410 and finally
in 412 at which point substantially all of the metal is leached
out. As will be understood, additional E-VATs may be added in
series, or in parallel, to the apparatus illustrated in FIG. 14. A
rinsing solution of clean water can be added at the end of auger
413 as shown in 194 of FIG. 12.
[0062] The need for multiple E-VAT units in series should be
obvious to one skilled in the field. Fresh ore entering the top of
E-VAT unit 404 may be reactive enough to precipitate dissolved
metal thus preventing the metal from leaving the vessel. This could
possibly happen if the ore contained sulfides and the dissolved
metal was gold. Another function of the series arrangement is to
prevent ore particles from short-circuiting the E-VAT unit and not
receiving the full leaching time necessary to dissolve all of the
metal contained in the particle.
[0063] Still another advantage of the series arrangement of
multiple E-VAT units and associated electrolytic cells, pumps and
tanks is the ability to selectively leach and remove intended
minerals or metals. In one example utilizing an apparatus
illustrated in FIG. 14, the Inventor operated the apparatus for
leaching an ore containing polymetallic sulfides, with solutions
containing both sodium chloride and sodium bromide which, when
passed through a positively-charged flow-through electrode, were
partially converted in chlorine and bromine and their compounds. It
was observed that the metals in the sulfides were leached in the
following order. First, the lead sulfides dissolved, followed by
the zinc sulfides and then the copper sulfides dissolved. This was
followed by dissolution of gold while the contained silver remained
in the ore as silver chloride and silver bromide.
[0064] Using a system such as illustrated in FIG. 14, a
polyrnetallic ore containing metal sulfides can be treated in
sequence. First the lead is leached in E-VAT unit 404 and recovered
in flow-through electrolytic cell 419, then the zinc is leached in
E-VAT unit 406 and recovered in flow-through electrolytic cell 420.
Next the copper is leached in E-VAT unit 408 and recovered in
flow-through electrolytic cell 421. Gold is then leached in E-VAT
unit 410 and recovered in flow-through electrolytic cell 422.
Finally, silver is leached in E-VAT unit 412 and recovered in
flow-through electrolytic cell 423.
[0065] It should be obvious to one skilled in the art, that the
lixiviants used in a multiple stage process can be diverse. For
example, to recover lead and zinc from polymetallic sulfide ores, a
starting solution containing only sodium chloride could be used
while the addition of sodium bromide may increase the recovery of
copper in the next stage and increases the recovery of gold in the
gold stage. Silver requires the use of a different lixiviant than
used in the previous stages as the silver halides are insoluble in
water, but the silver can be recovered in this stage by the use of
solutions containing thiosulfate, ammonia, salt brine, or a number
of organic compounds.
[0066] It will be understood by one skilled in the art that the
solutions could also flow through multiple units in a
counter-current direction with or without passing through an
electrolytic cell. Such a flow scheme may be of use to increase the
metal content of the pregnant solution prior to stripping in an
electrolytic cell. It also should be understood by one skilled in
the art, that other methods of removing metals from pregnant
solutions could be used prior to lixiviant regeneration including
cementation with another metals, ion exchange, or crystallization
of a metal salt such as lead chloride recovered by simply cooling a
saturated hot solution.
[0067] It should also be understood by one skilled in the art, that
this multiple stage process can be used to treat a vast variety of
solids whereby the solids are treated by different lixiviants for
different objectives. The solids could be ores containing metals or
scrap materials such as granulated electronic circuit boards. The
solids could also be contaminated soils where there is a need to
remove environmentally hazardous compounds as simple as salty soil
to that containing radioactive compounds. One skilled in the art
will also readily recognize that the liquids used need not be
confined to water solutions but could as well be any number of
organic liquid compounds.
[0068] FIG. 15 illustrates yet another embodiment of the present
invention. It depicts a flow chart of the operational steps for a
method of recovering metal, in particular, gold, from ores
requiring finer particle size preparation for liberation of their
mineral values. Crushed ore, prepared by any number of conventional
methods, enters ball mill 501 through process stream 500 and
discharges through process stream 502 where additional water is
added from process stream 509. The ground ore slurry enters
classifier 503 where oversize material is separated and returned to
the ball mill 501 through process stream 504 while diluted
undersize material flows through process line 505 into thickener
506 where the ore slurry is thickened to a pulp density between 40
to 70 percent, more preferably 60 to 70 percent. The excess water
from the thickener is decanted through process line 507 into
storage tank 508 while the thickened slurry is pumped (pump not
shown) through process line 510 into mixing tank 511 where
lixiviant is added. The lixiviant should have a pH between 3 and 8
(dependent upon the chemistry of the ore), a sodium chloride
content of between 0.1 and 25 percent, a sodium bromide content
between 0.05 and 5 percent and an oxidation-reduction potential (as
measured with a calomel-platinum probe) in excess of +650
millivolts, more preferably +850 to +950 millivolts, due to the
generation of dissolved chlorine and bromine and their compounds.
This lixiviant is generated in the positively charged flow-through
electrode of electrolytic cell 529. Sufficient lixiviant is added
to dilute the pulp density of the incoming ground ore slurry to
between 10 and 35 percent solids, more preferably to 25 percent
solids. It should be noted that all equipment from the mixing tank
511 to the end of the process should be constructed of
non-corroding material, and in an embodiment is constructed of HDPE
plastic, and should be totally enclosed to prevent any loss of
chlorine or bromine vapors. The ground ore slurry, with the added
lixiviant, leaves mixing tank 511 through process line 512 into
pump 513 where it is injected into the bottom of reactor 515
through process line 514, it departs reactor 515 through process
line 516 where it enters pump 517 and is injected into the bottom
of reactor 519 through process line 518. It departs through process
line 520 into pump 521 where it is injected into the bottom of
reactor 523 through process line 522. In one embodiment mixing tank
511 and reactors 515, 519, 523 are cone-bottomed covered vessels of
rotary-cast hi-density polyethylene (HDPE). The conical shape of
the bottom insures that all of the ore particles are in motion and
subject to the action of the lixiviant. It has the added advantage
of allowing any occasional coarse gold particles (due to their
heavy nature) to remain trapped in the vessel until they dissolve.
A minimum of three reactors is utilized in this embodiment to
prevent any material from short circuiting the vessel and not
getting full time exposure to the lixiviant. The slurry residence
time in each reactor 515, 519, and 523 is from less than 30 minutes
to about 4 hours, preferably about 1 hour, dependant upon the
natural chemistry of the ore.
[0069] The ore slurry, with dissolved metals, leaves reactor 523
through process line 524 into pump 525 which transfers it to
thickener 527 through process line 526. In thickener 527, the
solids are separated from most of the liquid containing the
dissolved metals. This pregnant solution leaves through process
line 528 where it is joined with additional pregnant solution from
filter 544 through process line 543. The combined streams flow into
flow-through electrolytic cell 529 where gold and other metals are
deposited in and on the negatively charged flow-through electrode,
as also depicted in FIG. 7. The now barren solution flows into the
inter-electrode space, where a portion of it flows through process
line 546 to evaporator 536 (to maintain salt water balance) while
the remainder flows through the positively-charged flow-through
electrode where both chloride and bromide are oxidized to chlorine
and bromine and their compounds. This is now the lixiviant which
leaves the flow-through electrolytic cell 529 through process line
530 where it is stored in lixiviant tank 531 from which it leaves
through process line 532 into pump 533 which injects it through
process line 534 into the bottom of mixing tank 511.
[0070] The thickened leached ore is pumped from thickener 544 (pump
not shown) into filter 544 where additional pregnant solution is
removed through process line 543. Within the filter 544, the filter
cake is rinsed with fresh water (source not shown) to removed any
entrained lixiviant. The rinsed filter cake, which is the leached
ore residue, is then sent to disposal shown as 545. This disposal
should be upon a liner to prevent any migration of trace amounts of
metals into the environment.
[0071] The rinse solution from the filter 544 leaves through
process line 542 and enters flow-through electrolytic cell 541. It
enters between the positive and negative charged flow-through
electrodes as shown in FIG. 5. Any residual gold and other metal is
recovered within the negatively-charged flow-through electrode
which also generates an excess of dissolved hydrogen gas. This
solution leaves through process line 540. A portion of the process
stream flows through the positively-charged flow-through electrode
where some of the residual chloride and bromide is oxidized to
chlorine and bromine and their compounds and leaves through process
line 539 where it is mixed with the solution from process line 540
in tank 538 where the dissolved hydrogen reduces the chlorine and
bromine contained in process line 539 back to harmless chloride and
bromide. The now neutralized dilute saline solution leaves tank 538
through process line 537 into evaporator 536. This could be any
commercial evaporator or simply a series of small evaporation
ponds. The purpose of this step is to increase the concentration of
dissolved salts to match that of the lixiviant. The now
concentrated salt solution is fed into lixiviant tank 531 through
process line 535. In another embodiment, the amount of solution
entering the evaporation step from line 546 can be dramatically
reduced by grinding the ore in a spent lixiviant solution rather
than fresh water.
[0072] The E-VAT continuous-flow counter-current leaching system of
the present invention has the ability to replace current
heap-leaching technology commonly used in the mining industry. In
heap-leaching technology, a large pile of ore is placed on an
impervious leach pad and sprayed or irrigated with leaching
solutions which migrate down through the ore, dissolving metals. In
many cases, the heaps continue to have additional ore added to them
until they reach enormous size, over hundreds of millions of tons.
These pads are saturated with the leaching solution. In the case of
gold and silver ores, the leaching solution contains cyanide. In
the case of copper ores, the leaching solution contains sulfuric
acid and iron salts. Thus, at the end of their economic life, heap
leach pads may contain enormous amounts of toxic materials in the
solutions which leads to potentially catastrophic environmental
disaster risks. The E-VAT continuous-flow counter-current leaching
system leaches the ore and then rinses the leached ore on a
continuous basis so that there is no accumulated environmental risk
like there is in a heap leach. Thus the risk to the environment is
drastically reduced, if not eliminated.
[0073] FIG. 16 illustrates another embodiment of this invention.
The figure is a cross section of a typical in-situ leaching
situation for uranium similar to those discussed by Hard et al. in
U.S. Pat. No. 3,708,206 and Habib, Jr., et al. in U.S. Pat. No.
4,312,840 and Camp, et al. in U. S Pat. No. 4,476,099. In this
diagram, a porous ore horizon 601 containing valuable uranium
deposits, is sandwiched between two impermeable beds 602 and 603
which protect underlying rock formation 605 and overlying gravel
604 from contamination by solutions originating in ore horizon 601.
In this case, a lixiviant containing alkali metal bicarbonate, or
carbonate and hypochlorite solutions at a pH in excess of 7, more
preferably between 8-10 is injected through process line 615 into
Injection Well 606 where it enters porous ore horizon 601 wherein
the lixiviant dissolves uranium minerals. The metal-laden lixiviant
is withdrawn from the porous ore horizon 601 by Recovery Wells 1
and 2, 607 and 608, where it flows through process line 607 into
pregnant solution tank 608 and then through process line 609 into
precipitation apparatus 610 where the pH of the pregnant solution
is lowered and sufficient phosphate is added to precipitate the
contained uranium values as discussed, for example, by Camp, et al.
in U. S Pat. No. 4,476,099. The mechanism of recovering the
precipitate is not shown in this diagram. The now barren solution
leaves the precipitation apparatus 610 through process line 611
where it enters flow-through electrolytic cell 612. The details of
this particular embodiment of the flow-through cell 612 are
depicted in FIG. 4. The pH of the lixiviant is increased and
restored to the range of 8-10 within the negatively charged
flow-through electrode by the electrolytic reduction of the water
according to the equation 2H.sub.2O+2e.sup.-.fwdarw.H.sub.2+2OH
contained chloride ions are oxidized to chlorine according to the
equation 2Cl.sup.--2e.sup.-.fwdarw.- Cl.sub.2 which dissolves in
the alkaline solution to form hypochlorite according to the
following equation Cl.sub.2+H.sub.2O.fwdarw.Cl.sup.-+H.s-
up.-+HOCl. The power source to provide the direct electric current
for the flow-through electrolytic cell can be, for example, solar
cells, wind generators or conventional power grid. The now
regenerated lixiviant with pH and hypochlorite content restored,
leaves the flow-through electrolytic cell 612 through process line
613 into lixiviant storage tank 615, thus completing a closed
chemical circuit for the production of uranium. This embodiment is
particularly applicable to, for example, the Anderson uranium mine
in Yavapai County, Ariz.
[0074] Although this embodiment specifically refers to the recovery
of uranium by in-situ methods, this is not intended to limit this
use of this invention to uranium as numerous other metals such as
gold, silver, copper, lead, zinc, or cobalt, to name a few, using
appropriate lixiviants that can be generated or regenerated using a
flow-through electrolytic cell of this invention.
[0075] FIG. 17 is a schematic diagram showing one embodiment of
this invention whereby treated irrigation water is used to irrigate
growing crops. In this diagram, untreated water in pond 701 is
pumped through intake line 702 by pump 703 through line 704 into
the inter-electrode chamber of flow-through electrolytic cell 705.
In this embodiment, the negatively charged electrode 706 is
composed of a conducting wire mesh or screen such as copper or
stainless steel, while the positively charged electrode 707 is a
flow-through electrode of graphite felt as depicted in FIG. 1. The
majority of the water passes through electrode 706 where it
undergoes reduction by the electrochemical process of decomposing
water where 2H.sub.2O+2e.sup.-.fwdarw.H.sub.2(gas)+2OH.sup.-
thereby also increasing the pH of the water. The water becomes
saturated in dissolved hydrogen gas. This water flows through line
708 and either through line 709 to line 711, or alternatively is
stored in storage tank 710 prior to flowing into line 711 and then
to a field of irrigated crops 712 where it is used as irrigation
water. If storage tank 710 is used, it is preferably made from an
electrical non-conductor such as HDPE, otherwise electrons may flow
from the water to the tank. A minority of the feed water in
flow-through electrolytic cell 705 flows through the positively
charged flow-through electrode 707 where some of the water is
oxidized according to the reaction
2H.sub.2O-4e.sup.-.fwdarw.O.sub.2(gas)+4H.sup.+- , thus creating an
acidic oxidizing water that may be disposed of, or alternatively,
used to control weed growth. The mechanism of controlling flow rate
through each electrode can either be controlled by valves (not
shown) but normally is self-regulating by the difference in
permeability between the open wire mesh or screen of the negative
electrode and the tight spacing in the graphite felt of the
positive electrode. The graphite felt is preferred due to its
resistance to attack by the oxidants generated with the positively
charged electrode where metals would rapidly corrode.
[0076] The foregoing discussion of the invention has been presented
for purposes of illustration and description. The foregoing is not
intended to limit the invention to the form or forms described
herein. Although the description of the invention has included
description of one or more embodiments, and certain variations and
modifications, other verifications and modifications are within the
scope of the invention, e.g., as may be within the skill and
knowledge of those in the art, after understanding the preset
disclosure. It is intended to obtain rights which include
alternative embodiments to the extent permitted, including
alternate, interchangeable and/or equivalent structures, functions,
ranges or steps to those claimed, whether or not such alternate,
interchangeable and/or equivalent structures, functions, ranges or
steps are disclosed herein, and without intending to publicly
dedicate any patentable subject matter.
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