US3819231A

US3819231A - Electrochemical method of mining

Info

Publication number: US3819231A
Application number: US00346013A
Authority: US
Inventors: F Fehlner
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-03-29
Filing date: 1973-03-29
Publication date: 1974-06-25
Anticipated expiration: 1991-06-25

Abstract

An in situ electrochemical method for extracting the mineral values from an ore body without greatly disturbing or polluting the ecology of the area. Holes are drilled into the ore body which is then fractured and propped. A leachant, introduced through the drill holes and cracks, solubilizes the mineral values in the ore. Anodes and cathodes are introduced into alternate drill holes and a DC electric potential is applied between them. The solubilized mineral values move to the cathode where they plate out as a metal. The leachant is simultaneously regenerated at the cathode. Thus leaching and plating continue in a cyclic process within a sealed portion of the ore body. The metal is recovered by removing the cathode from the drill hole.

Description

United States Patent [191 Fehlner ELECTROCHEMICAL METHOD OF MINING [76] Inventor: Francis P. Fehlner, 83 E. Fourth St.,

Corning, NY. 14830 [22] Filed: Mar. 29, 1973 [2]] Appl. No.: 346,013

I 52] U.S. Cl. 299/4, 204/106 [51] 'lnt.Cl. E2lb 43/28, E2lc 41/14 [58] Field of Search 299/3-6; 204/180 R, 106

[56] References Cited UNITED STATES PATENTS 989,802 4/1911 Rennie 204/106 2,761,829 9/1956 Dolloff 299/6 X Primary Examiner-Ernest R. Purser [111 3,819,231 June 25, 1974 [5 7] ABSTRACT An in situ electrochemical method for extracting the mineral values from an ore body without greatly disturbing or polluting the ecology of the area. Holes are drilled into the ore body which is then fractured and propped. A leachant, introduced through the drill holes and cracks, solubilizes the mineral values in the ore. Anodes and cathodes are introduced into alternate drill holes and a DC electric potential is applied between them. The solubilized mineral values move to the cathode where they plate out as a metal. The leachant is simultaneously regenerated at the cathode. Thus leaching and plating continue in a cyclic process within a sealed portion of the ore body. The metal is recovered by removing the cathode from the drill hole.

22 Claims, 3 Drawing Figures PATENTEDJUN25 I974 Fig.

Fig.

ELECTROCHEMICAL METHOD OF MINING BACKGROUND OF THE INVENTION It is desirable, and often necessary, to extract mineral values from an ore body with a minimum of pollution and disturbance of the ecology of an area. Competition for land use between mining, ranching, forestry, agricultural, urban, hydraulic, and recreational interests creates a situation in which mining must often coexist with at least one other use of the land. In the past, conflicts were usually resolved by mutual exclusion, but such a course is now becoming more and more difficult.

Common mining methods in current use for metallicore deposits include dredging, open pit, underground shaft, and hydraulic mining. Hydraulic mining and dredging are used in areas of the world where mining debris can still be disposed of easily. In other words, no competing land use interferes with the destruction of the ecology of the area. i

In the United States, shaft and open pit mines are the chief types. In shaft mines, the vein or ore body must be rich enough so that the costs of blasting, hauling, sorting, crushing, milling and smelting or refining can be recovered. This is an expensive mode of mining and can bedestructive to the ecology of an area through tailing piles and mine and mill drainage.

Open pit mining, which is related to strip mining, is

less expensive, buteven more destructive to the ecol-- ogy of an area. Topsoil and overburden are stripped from the ore body, laying bare subsoil and rock. The ore itself is broken and scooped up for transportation to the mill. At the mill, it is separated from barren material and then leached or smelted. The leaching is followed by electrowinning in which the solubilized mineral values are deposited as a metal at the cathode of an electrochemical cell.

It has been discovered that all these various mining processes can be carried out in the ore body itself, so that tailing piles, mine drainage and mill effluent are eliminated. In the present invention, hereinafter referred to as electromining, techniques of the oil well industry, e.g., drilling, fracturing, and propping, are combined with chemical leaching and electrolysis to obtain an in situ, cyclic process for recovery of mineral values from an ore body. Although portions of the electromining process of the present invention are familiar to those skilled in the art of mining, the combination of steps which forms the present invention has not been practiced heretofore.

The petroleum industry is not the only one that uses a well to recover a liquified ore from the earth. The recovery of water-soluble salts through drilled wells and the Frasch process for sulfur recovery are additional examples in which the mineral values are liquified and pumped to the surface of the earth. The same concept is being applied to copper mines, where in situ acid leaching of broken ore is carried out. The pregnant leach liquor is pumped to a mill where cementation, solvent extraction, or electrowinning is used to recover the metal. The barren liquor is then returned to the mine for further leaching of broken ore. Electromining differs from this process in that all steps in the electromining process of the present invention take place in the ore body itself, so that no transport of ore or leach liquor is necessary. Also, the present invention does not require the extensive surface structures utilized in this prior-art method.

In a variation of electrowinning, called electrooxidation, an oxidizing agent is generated electrolytically in a vat of ore, water, and chemicals. The oxidizing agent reacts with the ore to make subsequent leaching of the mineral values in the ore easier to carry out.

Electromining is distinguished from electroreclamation, which is used to improve agricultural land containing an excess of water-soluble: salts, in that electromining is utilized to recover mineral values from an ore which is water-insoluble under normal conditions. ln electroreclamation, a potential applied to electrodes buried in wet soil causes already soluble ions to drift to their respective electrodes where they can be pumped out of the soil. The purpose of electroreclamation then is desalination of the topsoil, while that of electromining is recovery from an ore body of mineral values in the form of a metal.

Electroosmosis can also occur during electroreclamation. It is practiced in a manner similar to electroreclamation, but leads to the removal of excess water from a surface or subsurface soil layer so that the load-bearing properties of the soil are improved.

, Another modification of electroreclamation, called electroprecipitation, is used to precipitate insoluble deposits in a porous soil or rock formation and thereby render it impervious to water. This process is useful in conjunction with electromining in that it can be used to form a water-impervious barrier around the ore body.

SUMMARY OF THE INVENTION AND OBJECTS It is accordingly. an object of this invention to provide a useful method for recovering mineral values from an ore body.

It is further an object to provide a method which is non-polluting and offers little disturbance to theecology of the mining area, since it is based on in situ recovery of mineral values from the ore body. Thus, tailing piles, smelter fumes, noise, slagpiles, mine drainage, and mill effluent of present mines and mills are largely eliminated.

It is further an object to provide a method which efficiently and economically uses electrical power in the recovery of mineral values, thereby making possible the mining of low-grade ore bodies which are currently of only marginal economic value.

It is further an object to provide a method in which there is no large scale transfer of ore or leach solution, thus avoiding the scars of open pit mines and the cost of the extensive surface works :required for milling, smelting, leaching, electrowinning, and refining.

It is further an object to provide a method in which the leach solution is regenerated and/or generated within the ore body so that the method requires a minimum amount of water and chemicals.

It is further an object to provide a method which avoids the dangers of underground shaft mining, such as explosions, cave-ins, poisonous vapors, heat, dust, silicosis, and radiation.

It is further an object to provide a method for extracting mineral values in difficult environments such as mines located at high altitudes, under water, or at great depths in the earth.

It is further an object to provide a method which can be used for mining on the Moon and planets other than Earth, by utilizing the closed cycle of electromining with its limited need for water, gas, and chemicals and its efficient use of electrical power.

In accordance with this invention, holes are drilled into an ore body which is subsequently fractured and propped, if the ore body is not porous. An anode is placed in at least one drill hole and a cathode in at least one other drill hole, both electrodes being placed adjacent to the ore body. A leachant is introduced into the ore body in the vicinity of the anode and cathode. The leachant solubilizes the mineral values in the ore body. A DC potential is applied between the anode and cathode, thereby causing electrodeposition of the solubilized mineral values as a metal on the surface of the cathode. The metal is recovered by removing it along with the cathode from the drill hole.

Other objects, features, and advantages of this invention will become apparent during the course of the following detailed description and the attached drawing, on which by way of example, only the preferred embodiments of this invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan view of the drill holes in and around an ore body, as required for electromining. Above ground details are not shown.

FIG. 2 is a cross-sectional view of the drill holes and ore body, taken along line 22 in FIG. 1.

FIG. 3 is a cross-sectional view of the model used to test electromining.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with this invention, an ore body 8 delineated by boundary 9, whose location in or under the surrounding barren ground 10 is already known or is determined by geological exploration, is proven out by drilling a series of test holes, at least one inch in diameter, 11, 12, and 13. These drill holes provide physical means of gaining access to the ore body. If the ore body, whether lode or placer, proves to be economically viable for electromining, additional holes are drilled so that the spacing between

holes

12 and 13 is from 2 to 1,000 feet, as determined by the porosity of the ore body. The greater the porosity, the further apart the holes are spaced.

Pipe casing, 14, either metal or insulator, is used to line the upper portions of the holes in the regions where the holes pass through an unstable formation 15, such as topsoil or gravel. Portions of the holes drilled through rock 16 can be left uncased.

The flow patterns of underground water within and without the ore body 8 are then determined by examining flow patterns between

holes

12, 13 and holes 11. This is done to determine whether the leachant and solubilized mineral values hereinafter described can escape from the ore body to contaminate the surrounding aquifer. If the ore body is completely surrounded by water-impervious rock 16, then electromining can proceed directly. However, if a porous geological formation 17 is present, than an artificial dam must be formed around part or all of the ore body. This is done by either injecting sealant 18, such as a plastic, through hole 11 into the pores in formation 17, or utilizing electroprecipitation to close the pores. If necessary, additional holes are drilled and/or cracks are formed in formation 17 by explosives placed in holes 11, to receive the sealant 18. Sealant which enters the pores is shown by region 19 in FIG. 2.

The circumferential ring of holes 11, spaced at 2 to 1,000 foot intervals around that portion of the ore body which is to be electromined, is an important aspect of the process when the ore body is located in porous surroundings that would not retain the leachant. Hole spacing is determined by the porosity of formation 17; the greater the porosity, the larger the spacing. The underground darn created by injecting sealant 18 into holes 11 forms an artificial basin which contains the water and chemicals, thus preventing loss of mineral values and contamination of the surrounding aquifer.

Any faulting of the earth producing a fault line which extends from outside the ore body, thence into it, can also provide a leakage path for water and hence must be sealed in a manner similar to that used in sealing the porous formation 17.

Cracks and fissures 20 are formed in the ore body by fracturing it, if the ore body is not porous enough to allow water to permeate it easily. This process involves detonation of explosives in some or all of drill holes 12 and 13 at the same level as, and adjacent to the ore body. The resulting blast breaks up the ore body, leaving cracks 20 through which water and chemicals can penetrate the ore body. These cracks eventually tend to close up again, so it is advantageous to prop them open by injecting sand or glass beads 21 into them. Drill holes 12 and 13 are then cleared of debris generated by the fracturing and propping and an electricallyinsulating casing 22, having perforations 7 through it, is introduced opposite the ore body to hold the broken ore in place. This casing can have a smaller diameter than the upper casing 14.

Removable plugs or caps 23 are attached to the upper casing 14 to seal the drill holes 12 and 13. These plugs are used to control the composition and pressure of the atmosphere 24 in the holes above the top of the water line 25. The

electrodes

26 and 27 pass through an electrically-insulated bushing 28 in the plugs 23.

The water level 25 is adjusted by adding or removing water from that portion of the ore body enclosed by the impervious barrier delineated by holes 11, so that the water level 25 is near or above the top of the ore body.

The electrodes are then inserted, anode 26 and cathode 27 preferably being alternately disposed in

holes

12 and 13 respectively. Thus, holes 12 become anode compartments and holes 13 become cathode compartments.

The actual pattern of anodes and cathodes is determined by the geometry of the ore body 8. A minimum of one anode and one cathode are required. For a small ore body, a single anode could by surrounded by a plurality of cathodes. For a large ore body, anodes and cathodes could be spaced alternately in close-packed array, as illustrated in FIG. 1.

The anodes 26 are preferably of the inert type; that is, they do not dissolve during the electrodeposition of metal on the cathode. Examples are graphite, tin oxide, silicon-iron, silicon-nickel, or platinum-coated titanium. The cathodes 27 on the other hand, are usually made from the same metal as that being recovered from the ore body 8.

Leachant 29 is formed by introducing chemicals into the water whose level is indicated by water level 25. The chemicals are introduced through one or more of the plugs 23 into drill holes 12 and 13, or generated electrolytically in situ from chemicals also introduced through one or more of the plugs 23 into drill holes 12 and 13. A separate hole containing no electrodes may also be used to introduce the chemicals into the ore body in the vicinity of the anode and cathode.

The leachant is a water soluble chemical such as acid, base, or salt, which chemically reacts with the waterinsoluble metal compounds constituting the mineral values in the ore. The products of the reaction are water-soluble metal compounds. In this way, the mineral values in the ore are solubilized.

The leachant 29 in drill holes 12 and 13 enters the ore body through perforations 7 in casing 22, and thence through the natural porosity of the ore and through cracks and fissures formed by fracturing the ore body. Many of these cracks and fissures emanate from the sides of the drill holes and extend into the ore body, eventually reaching the adjacent drill holes which contain electrodes of opposite polarity.

A DC power supply 30, connected between the anodes 26 and cathodes 27, supplies a DC potential of sufficient magnitude to reduce the solubilized mineral values to a metal 31 on the cathode 27. Electroplating current densities at the cathode surface of 0.05 to 50 A/dm are preferably used during deposition, as practiced by those skilled in the art of electroplating. The process is carried out at the temperature of the ore body, although the leachant can be heated to a higher temperature, as by the injection of steam, to speed the leaching and electroplating processes.

The metal 31 electroplated on the cathode 27 is recovered by removing the cathode 27 from the cathode compartment, along with the removable plug 23. The metal can then be further refined if necessary for the proposed use.

During electromining, the power supply 30 is operated continuously or intermittently, depending on the rate of leaching. If the cation concentration in the cathode compartment falls too low, then hydrogen is generated and current efficiency for electroplating metal decreases. Hence it is advantageous to electrolyze periodically, but leach continuously, when leaching is the rate limiting step in electromining.

It is well known in the practice of electroplating that the DC potential provided by power supply 30 is a constant voltage DC with or without a superimposed pulsed DC voltage of opposite polarity. The pulsed DC voltage of opposite polarity, which causes deplating of the cathode deposit, is produced by power supply 32 which is superimposed on the constant DC plating voltage supplied by power supply 30 by closing switch 33. The product of deplating current and deplating time must be kept smaller than the product of plating current and plating time. Otherwise, no metal deposits on the cathode.

In electroplating, such a combination of voltages is utilized to improve the uniformity of the metal electroplated on the cathode. This same technique can be applied to electromining to improve the uniformity of the cathode deposit, thereby preventing growth of metal dendrites into the ore body.

Although the upper portions of the drill holes 12 and 13 can be cased with either metal or insulating pipe,

any casing in the vicinity of the ore body must be formed of a perforated insulator 22 such as glass-fiberreinforced epoxy pipe. The perforations 7 allow leachant and solubilized mineral values to pass through while the insulator avoids electroplatingof metal on the outside of the casing 22 rather than on the cathode 27 itself.

The leachant 29 may be an inorganic acid which reacts directly with an oxidic ore to form a water-soluble metal salt. Bubbles of carbon dioxide are formed during this process if carbonates are present in the ore body 8 or surrounding formations 16 or 17. However, these bubbles are helpful in that they serve to keep the cracks 20 open.

In the case of a sulfide ore, a simple mineral acid is insufficient for leaching. An oxidizing agent such as oxygen or ferric sulfate is also needed to oxidize the sulfide ore and free the metal ions so that they can react with acid to form a soluble salt.

The oxidizing agent can be introduced in one of several ways. For instance, the atmosphere 24 over the leachant 29 can be composed of oxygen-rich air which is pressurized to force it to dissolve in the leachant. A chemical oxidizing agent such as NaOCl or Fe (SO can be introduced along with the leachant. An oxidizing agent such as NaOCl can be generated in situ by the electrolysis of NaCl.

In the case of a native metal, it: is believed that electromining occurs by anodic dissolution. The metal particles such as gold located between the anode and cathode are polarized by the DC potential applied across the electrodes. Ions in the leachant are attracted to the dipole thus formed, where they react with the native metal, forming a soluble salt.

The cation of the soluble metal salt produced in anodic dissolution or by the reaction of the leachant 29 with the mineral values in the ore body 8 diffuses to the cathode 27 where the metal ion is reduced electrolytically to a metal 31. The process is speeded up by forcing the leachant back and forth between anode and cathode compartments by alternately pressurizing the atmosphere 24 in the anode and cathode compartments. Simultaneously, electrical power can be applied continually to the electrodes, but it can be intermittently applied only when the leachant 29 enters the cathode compartment 13. A pump 34 connected between the anode and cathode compartments can be used to implement this process by alternately pressurizing the anode and cathode compartments.

A second method for moving the leach solution through the ore body is to adjust the water level in the ore body and drill holes so that pump 34 transfers leach solution rather than gas continuously from cathode compartment to anode compartment. In this way the renewed leachant is forced through the ore body where it leaches the mineral values from the ore. Simultaneously, the pregnant liquor is exposed to the cathode for electrodeposition of the mineral values as a metal.

At the same time that metal is being electrodeposited on the cathode, the leachant is regenerated in the cathode compartment. Simultaneously, an oxidation reaction occurs at the anode. The product of this anodic oxidation may itself act as a leachant or oxidizing agent, as in the case of the chloride ion. Chloride from sodium chloride is oxidized to chlorine, which in turn reacts with sodium hydroxide produced at the cathode thus forming an oxidizing agent, sodium hypochlorite. By reaction and electrolysis then, the initial leachant is cycled between the electrodes and the ore body so that only a limited amount of leachant is needed to carry out electromining.

The ideal concentration of leachant is maintained in the ore body by monitoring the pH and keeping it constant. The monitoring is done by removing a sample of leachant from a drill hole and measuring its pH, or by lowering a pH electrode into the leachant in a drill hole and remotely monitoring the value of pH. lf acid leaching is employed, then a rise in pH indicates exhaustion of the leachant and more acid must be added through one or more of plugs 23. In addition to decreased leachant concentration, loss of acid can lead to unwanted gelatinous precipitates of metal hydroxides. These form in the cracks 20, clogging them and slowing the rate of ionic movement. For instance, iron hydroxide forms at pH greater than 3, so that during acid leaching of an ore body containing iron, the pH should be kept less than 3 if gelatinous precipitates are to be avoided.

Conversely, if complex ion formation is used, as with cyanides or chlorides, then pH is maintained in the range of stable complex ion formation. For instance cyanide solutions are kept at a pH of 10 to 13.

The rate of electromining is controlled by the rate of diffusion of leachant into the ore and rate of diffusion of solubilized mineral values out of the ore. Ion drift caused by the applied field is very small, since the voltage required to maintain the preferred cathode electroplating current density of 0.05 to 50 A/dm is small. As a result, any stirring of the leachant by bubbles generated in situ or by forced leachant flow under a pressure differential increases the rate of ion movement and thereby increases the rate of electromining.

The method of electromining has been reduced to practice on a laboratory scale. The model used in testing the method of electromining is shown in FIG. 3.

Broken ore and gangue 40 and a suitable leachant 41 are contained in an impervious enclosure 42, such as a glass jar. An electrically-insulating cathode compartment 43 made of plastic and containing perforations 39 is inserted into the gangue and broken ore 40 and leachant 41 so that leachant but no ore or gangue is enclosed within the compartment 43. A wire cathode 44 is placed within the cathode compartment 43 so that it dips below the surface 45 of the leachant 41. An inert anode 46 such as graphite is also inserted into the broken ore and gangue 40 and leachant 41 so that it extends below the surface 45 of the leachant.

A DC power supply 47 is connected to the cathode 44 and anode 46 to supply electrons to the cathode for reducing the solubilized mineral values to metal 48 at the cathode. Simultaneously, leachant is regenerated at the cathode. Applied voltage is controlled by proper adjustment of the autotransformer dial 49 on the power supply 47, while current is indicated by a milliampere meter 50. All tests of electromining were carried out at ambient temperature, similar to conditions in an actual field situation.

To further illustrate the present invention and the manner in which it may be practiced, the following specific examples are set forth, using the model setup shown in FIG. 3.

EXAMPLE 1 A copper ore from Western Colorado, consisting of malachite and azurite in sandstone, was ground up and 10.936 g. of ore were placed between two layers of ordinary gravel in a 300 ml. beaker. The gravel weighed a total of 74.8 g. at the start of the example. Water was added to a depth of 1.3 in. in the cathode compartment and then 0.5 ml. of concentrated sulfuric acid were added. Gas bubbles were noted coming from the gravel as the acid attacked marble chips contained in the gravel. Additional acid was added as needed to maintain the leachant pH at a value less than 2, as measured using pH-indicator paper.

A graphite anode was inserted in the gravel-oreleachant mixture, opposite to the cathode compartment. A cathode was then formed from a spiral of copper wire and inserted into the cathode compartment at a distance of 1.3 in. from the anode. The area of the cathode was 0.013 dm A DC potential of approximately 3V was applied between the anode and cathode until a total of 4,450 Faradays had been passed through the electrolyte. The current density at the cathode was about 0.16 A/dm A total of 1.023 g. of copper, identified by its characteristic color, was recovered when the cathode was removed. To effect this recovery of metal, 7 ml. of concentrated sulfuric acid and 4.528 watt hrs. of electricity were required.

Calculations based on the above numbers show that the recovery of copper was 71 percent efficient on an electrical basis. The acid use rate was high due to reaction with the marble chips in the gravel. A total of 2.8 g. of gravel were lost during the electromining example, so a large amount of acid was used in unproductive side reactions. Such reactions can be minimized in the field.

EXAMPLE 2 Droplets of refined gold, which simulated native placer gold, were determined to weigh 832 mg. These droplets were added to ml. of tap water and 5 g. of sodium chloride in a 400 ml. beaker. Power was applied between a copper cathode and graphite anode. No cathode compartment was used in this example. During part of the time, a stainless steel cathode was substituted for the copper cathode. In both cases, a brown deposit was formed on the cathode. This brown deposit was analyzed by ESCA (Electron Spectroscopy for Chemical Analysis) and found to be gold. After 4 volts had been applied between the electrodes for 14 hrs. at a current density of about 0.1 Aldm 29 mg. of gold were recovered at the cathode. During this time, the leachant turned basic to red litmus paper.

The example was continued by mixing the remaining 803 mg. gold with common yard gravel and placing the combination in a 600 ml. beaker. A graphite anode and copper cathode were utilized again and the leachant was 8.5 g. sodium chloride in 100 ml. water. A voltage of 3.5V was applied between the electrodes for hrs. A total of 40 mg. gold was recovered at the cathode.

In a similar manner, native gold in NaCl, refined gold droplets in KCN, pyrargyrite in HNO zincite and Franklinite in HCl, Leadville silver ore in H SO /NaCl, native mercury and cinnabar in HCl and HCl/H SO galena in HNO and niccolite in H 50 were electromined at room temperature utilizing a setup similar to that used in Example 1. The conditions under which Examples 3 through 10 were undertaken are shown in Table I. A copper cathode and graphite anode were used in all of the examples except No. 3 in which a graphite cathode was used.

In an actual field situation, the values of the experimental parameters would differ somewhat from those recorded for Examples 1 through 10.

The metals recovered in accordance with the present invention are useful in art, industry, and trade. Further refining of the metal recovered at the cathode is necessary if two or more metals are recovered simultaneously from the ore. Single metals can be used directly as they come from the cathode since electrolytic deposition tends to eliminate impurities, thus providing a pure metal deposit.

Ores of various metals and mixtures of metals which are suitable for chemical leaching and electrodeposition at the cathode of an electrochemical cell may be employed in the process of the present invention. Such metals and mixtures include, for example, arsenic, antimony, bismuth, cadmium, chromium, cobalt, copper, gallium, gold, indium, iridium, iron, lead, manganese, mercury, nickel, osmium, palladium, platinum, polonium, rhenium, rhodium, ruthenium, selenium, silver, technetium, tellurium, thallium, tin, uranium, vanadium, and zinc.

It will be apparent to those skilled in the art that many variations and modifications of the invention as hereinabove set forth may be made without departing from the spirit and scope of the invention. The invention is not limited to those details shown which follow, except as set forth in the appended claims.

TABLE I EX. ORE REAGENT APPROXI- MATE CONDI- RESULTS AT TIONS CATI-IODE 3 l2! mg. native NaCl (5 g. in 3V, I mA, 70 Gold plated out gold I00 ml. H O) hrs. (no (American cathode River, Calif.) compartment) 4 763 mg. KCN (2.5 g. in 2% V, 28 hrs.. l44 mg. gold refined gold 100 ml. pH=l l recovered droplets buffered water) 5 8.6 g. HNO (0.4 ml. 5V, 167 hrs., Metal plated Pyrargyrite conc. in I50 pH=4 out (Red ml. 0)

Mountain, Calif-l 6 8.8 g. Zincite. HCl (0.5 ml. 4V, hrs., -l00 mg.

Franklinite, 20 B in 200 pH=2.5 metal (Franklin. ml. H O) recovered NJ.)

7 92.2 g. silver H 50 (37.7 4V, 2 mA, 148 670 mg. metal ore ml. conc.) hrs., pH=l recovered (Leadville, plus NaCl (1.5 Colorado) g.) in ml.

8 7 g. native HCl (2 ml. 20 3.5V, I mA, 16 mg. of metal mercury and B) plus H 50, I74 hrs., recovered cinnuhur (L9 ml. pH=2 (Sonmnu Cd, cone.) inlt) Calif.) ml. IMO

9 29.3 g. galena HNO (2.l ml. 3V, 0.6 mA, 982 mg.

(Eastern conc. in 20 ml. 884 hrs., metulliegray Colo.) H O) pH=l crystals recovered TABLE l-Continued EX. ORE REAGENT APPROXI- MATE CONDI RESULTS AT TIONS CATl-IODE I0 6.4 g. H 50 (1 ml. 3V, 1 mA, 304 148 mg. metal Nlccohte cone. m 20 ml. hrs., pH=l recovered (Ontario, H Canada) I claim:

1. A method for extracting mineral values from an ore body comprising the steps of:

drilling holes in said ore body,

placing an anode in at least one of said drill holes and adjacent to said ore body, said at least one of said drill holes thereby becoming an anode compartment, placing a cathode in at least one other of said drill holes and adjacent to said ore body, said other drill hole thereby becoming a cathode compartment,

providing said ore body with leachant in the vicinity of said anode and cathode, thereby bringing about solubilization of said mineral values,

applying a DC potential between said anode and said cathode, thereby causing electrodeposition of said solubilized mineral values as a metal on the surface of said cathode,

removing said cathode from said drill hole thereby recovering said metal.

2. A method according to claim 1 further comprising the step of forming an impervious barrier around at least part of said ore body.

3. A method according to claim 1 further comprising the step of opening cracks in said ore body, thereby facilitating access of said leachant to said ore body.

4. A method according to claim 1 further comprising the step of introducing leachant through at least one of said drill holes into said ore body.

5. A method according to claim 1 further comprising the step of generating said leachant electrolytically from chemicals introduced into said ore body through at least one of said drill holes.

6. A method according to claim 1 further comprising the step of heating said leachant above the temperature of said ore body.

7. A method according to claim 1 further comprising the step of casing said drill holes, thereby preventing collapse thereof.

8. The method according to claim 1 further comprising the step of easing said drill holes with perforated, electrically-insulating casings in the vicinity of the ore body.

9. A method according to claim 1 further comprising the step of sealing the tops of the anode and cathode compartments, thereby controlling the nature and pressure of the atmosphere in said compartments.

10. A method according to claim 9 wherein said atmosphere is other than air.

I]. A method according to claim I wherein the anode is inert.

12. A method according to claim I further comprising the step of imposing a pressure differential between said anode and cathode compartments thereby causing flow of said leachant through said ore body.

13. A method according to claim 1 further comprising the step of maintaining pH of said leachant constant.

14. A method according to claim 1 wherein the electroplating current density at the surface of said cathode is in the range 0.05 to 50 A/dm 15. A method according to claim 1 further comprising the steps of maintaining the pH of said leachant constant and maintaining the electroplating current density at the surface of said cathode in the range 0.05 to 50 A/dm 16. A method according to claim 1 further comprising the step of forming an impervious barrier around at least part of said ore body, opening cracks in said ore body, and casing said drill holes.

17. A method according to claim 1 wherein the ore is selected from the group consisting of malachite, azurite, native gold, pyrargyrite, zincite, Franklinite, Leadville silver ore, native mercury, cinnabar, galena and niccolite.

18. A method according to claim 1 wherein the leachant is selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, potassium cyanide, sodium chloride, sulfuric acid plus sodium chloride, and sulfuric acid plus hydrochloric acid.

19. A method according to claim 1 wherein the metal is selected from the group consisting of copper, gold, silver, zinc, mercury, lead, and nickel.

20. A method according to claim 1 wherein the cathode is selected from the group consisting of copper and stainless steel.

21. A method according to claim 1 wherein the anode is graphite.

22. A method for extracting mineral values from an ore body comprising the steps of drilling holes of at least one inch diameter spaced at 2 to 1,000 foot intervals in and around said ore body, injecting sealant into those holes surrounding at least part of said ore body thereby forming a water-impervious barrier around at least part of said ore body, opening cracks in said ore body by fracturing and propping said ore body adjacent to said holes drilled in said ore body, casing said drill holes to prevent their collapse, introducing at least one anode and one cathode into different drill holes in said ore body, providing leachant to said ore bodyin the vicinity of said anode and cathode, applying a DC potential between the anode and cathode so that the electroplating current density at the cathode surface is in the range 0.05 to 50 A/dm and removing said cathode from said drill hole thereby recovering the solubilized mineral values as metal electroplated on said cathode. l

Claims

2. A method according to claim 1 further comprising the step of forming an impervious barrier around at least part of said ore body.
3. A method according to claim 1 further comprising the step of opening cracks in said ore body, thereby facilitating the access of said leachant to said ore body.
4. A method according to claim 1 further comprising the step of introducing leachant through at least one of said drill holes into said ore body.
5. A method according to claim 1 further comprising the step of generating said leachant electrolytically from chemicals introduced into said ore body through at least one of said drill holes.
6. A method according to claim 1 further comprising the step of heating said leachant above the temperature of said ore body.
7. A method according to claim 1 further comprising the step of casing said drill holes, thereby preventing collapse thereof.
8. The method according to claim 1 further comprising the step of casing said drill holes with perforated, electrically-insulating casings in the vicinity of the ore body.
9. A method according to claim 1 further comprising the step of sealing the tops of the anode and cathode compartments, thereby controlling the nature and pressure of the atmosphere in said compartments.
10. A method according to claim 9 wherein said atmosphere is other than air.
11. A method according to claim 1 wherein the anode is inert.
12. A method according to claim 1 further comprising the step of imposing a pressure differential between said anode and cathode compartments thereby causing flow of said leachant through said ore body.
13. A method according to claim 1 further comprising the step of maintaining pH of said leachant constant.
14. A method according to claim 1 wherein the electroplating current density at the surface of said cathode is in the range 0.05 to 50 A/dm2.
15. A method according to claim 1 further comprising the steps of maintaining the pH of said leachant constant and maintaining the electroplating current density at the surface of said cathode in the range 0.05 to 50 A/dm2.
16. A method according to claim 1 further comprising the step of forming an impervious barrier around at least part of said ore body, opening cracks in said ore body, and casing said drill holes.
17. A method according to claim 1 wherein the ore is selected from the group consisting of malachite, azurite, native gold, pyrargyrite, zincite, Franklinite, Leadville silver ore, native mercury, cinnabar, galena and niccolite.
18. A method according to claim 1 wherein the leachant is selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, potassium cyanide, sodium chloride, sulfuric acid plus sodium chloride, and sulfuric acid plus hydrochloric acid.
19. A method according to claim 1 wherein the metal is selected from the group consisting of copper, gold, silver, zinc, mercury, lead, and nickel.
20. A method according to claim 1 wherein the cathode is selected from the group consisting of copper and stainless steel.
21. A method according to claim 1 wherein the anode is graphite.
22. A method for extracting mineral values from an ore body comprising the steps of drilling holes of at least one inch diameter spaced at 2 to 1,000 foot intervals in and around said ore body, injecting sealant into those holes surrounding at least part of said ore body thereby forming a water-impervious barrier around at least part of said ore body, opening cracks in said ore body by fracturing and propping said ore body adjacent to said holes drilled in said ore body, casing said drill holes to prevent their collapsE, introducing at least one anode and one cathode into different drill holes in said ore body, providing leachant to said ore body in the vicinity of said anode and cathode, applying a DC potential between the anode and cathode so that the electroplating current density at the cathode surface is in the range 0.05 to 50 A/dm2, and removing said cathode from said drill hole thereby recovering the solubilized mineral values as metal electroplated on said cathode.