OPTIMIZED ORE PROCESSING USING MOLTEN SALTS FOR LEACHING AND THERMAL ENERGY SOURCE

Abstract

A method for the electrolytic production of pure copper from copper-containing compounds dissolved in a high-temperature bath of molten salts which function as an electrolyte in an electrolytic cell. An electric current is passed between an anode immersed in the copper-ion rich molten salt bath and a cathode or cathode-lined kettle in which the molten salt bath is contained, thereby reducing the dissolved copper ions to form pure molten copper. The deposited molten copper collects at the bottom of the kettle and can be separated from the molten salt bath using conventional means.

Claims

1. A method of producing pure metallic copper in an electrolytic cell containing a molten salt electrolyte, the method comprising the steps of: providing a vessel for containing the molten salt electrolyte at a temperature of between 500 C. and 1200 C., said vessel comprising a bottom and walls extending upwardly from said bottom, wherein said vessel further comprises an outlet configured as a drain; providing at least one copper-containing compound; dissolving said at least one copper-containing compound in said molten salt electrolyte; providing at least one anode in liquid communication with said molten salt electrolyte; providing at least one cathode in communication with said vessel bottom; passing an electrical current through said anode and said cathode, thereby depositing molten copper at said cathode and producing gas at said anode; removing copper deposited at said cathode through the outlet in said vessel.

2. The method of claim 1, wherein said vessel further comprises a mechanical stirrer configured to aerate said molten salt electrolyte and any copper copper-containing compounds dissolved therein.

3. The method of claim 1, wherein said vessel is composed of fused quartz.

4. The method of claim 1, wherein said anode and said cathode are composed of graphite carbon.

5. The method of claim 1, wherein said electrolyte comprises at least one compound selected from the group consisting of the halide salts of alkali metals, alkaline earth metals, and magnesium.

6. The method of claim 1, further comprising the step of monitoring the electric potential of the molten salt electrolyte using a reference electrode.

7. A method of producing pure metals from slag obtained from the copper mining process using an electrolytic cell containing a molten salt electrolyte, the method comprising the steps of: providing an extraction vessel for containing a mixture of molten salt electrolyte and slag at a temperature of between 1000 C. and 1200 C., wherein said extraction vessel comprises a bottom and walls extending upwardly from said bottom and is configured with a mechanical stirrer to aerate the mixture of slag and molten salt electrolyte contained in the extraction vessel, thereby causing metal ions in the slag to be dissolved as metal ions in the electrolyte; wetting said slag in said molten salt electrolyte in said extraction vessel; removing metal ion-depleted slag from said extraction vessel; transferring metal ion-rich electrolyte from said extraction vessel to said electrodeposition vessel; providing an electrodeposition vessel in liquid communication with said extraction vessel, said electrodeposition vessel comprising: a bottom and walls extending upwardly from said bottom, and further comprising an outlet configured as a drain; at least one anode; at least one cathode in communication with said vessel bottom in said electrodeposition vessel; passing electrical current through said anode and said cathode in said electrodeposition vessel, thereby depositing molten metal at said cathode and producing gas at said anode; removing metal deposited at said cathode through the outlet in said vessel.

8. The method of claim 7, wherein said vessel further comprises a mechanical stirrer configured to aerate said molten salt electrolyte and any copper copper-containing compounds dissolved therein.

9. The method of claim 7, wherein said vessel is composed of fused quartz.

10. The method of claim 7, wherein said anode and said cathode are composed of graphite carbon.

11. The method of claim 7, wherein said electrolyte comprises at least one compound selected from the group consisting of the halide salts of alkali metals, alkaline earth metals, and magnesium.

12. The method of claim 7, further comprising the step of monitoring the electric potential of the molten salt electrolyte using a reference electrode.

13. An electrolytic cell for the production of pure copper metal, the electrolytic cell comprising: a molten salt electrolyte having at least one copper-containing compound dissolved in therein; a vessel for containing the molten salt electrolyte at a temperature of between 500 C. and 1200 C., said vessel comprising a bottom and walls extending upwardly from said bottom, wherein said vessel further comprises an outlet configured as a drain; at least one anode in liquid communication with said molten salt electrolyte; at least one cathode in communication with said vessel bottom; a source of electrical current in communication with said anode and said cathode.

14. The electrolytic cell of claim 13, further comprising a reference electrode for monitoring the electric potential of the molten salt electrolyte.

15. The electrolytic cell of claim 13, wherein said vessel further comprises a mechanical stirrer configured to aerate said molten salt electrolyte and any copper copper-containing compounds dissolved therein.

16. The method of claim 13, wherein said vessel is composed of fused quartz.

17. The method of claim 13, wherein said anode and said cathode are composed of graphite carbon.

18. The method of claim 13, wherein said electrolyte comprises at least one compound selected from the group consisting of the halide salts of alkali metals, alkaline earth metals, and magnesium.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1. is a schematic depicting one embodiment of the system and process of the present disclosure.

[0034] FIG. 2. is a flowchart of the process steps of the present invention.

[0035] FIG. 3 illustrates a schematic of the process steps described herein using molten salts as the low vapor pressure liquid, and using a heat exchanger to store and provide thermal heat.

[0036] FIG. 4. is a schematic diagram of a pilot plant for extracting metal ion into molten salt and electrodeposition of metal from the metal ions dissolved in molten salt.

DESCRIPTION OF THE INVENTION

[0037] The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the following non-limiting embodiments.

[0038] The invention includes an electrolytic cell for the production of copper from copper-containing compounds dissolved in a molten salt electrolyte. Preferably, the molten electrolyte is maintained at a temperature of between 500 C. and 1200 C. The copper-containing compounds can be added to the cell as a batch or on a continuous basis. The electrolytic cell employs anodes and cathodes, the cathode being in communication with the vessel containing the molten salt electrolyte. In the process of the invention, electric current is passed from the anode through the molten electrolyte to the cathode, reducing the ionic copper dissolved in the electrolyte and depositing metallic copper at the cathode.

[0039] The electrolytic cell of the present invention employs electrolytes comprised of molten halide salts, preferably chloride salts of alkali metals and/or alkaline earth metals. In other preferable embodiments, the molten salt electrolyte may comprise NaClKClZnCl.sub.2 or NaClKClAlCl.sub.4 in several eutectic compositions, including without limitation 2-aluminum and 3-magnesium chlorides mixed with Na and K chlorides, and 4-stable ionic liquids with various cations and chloride anions. In one embodiment, the electrolyte is composed of a 50:50 (mole-to-mole) mixture of NaCl and KCl salts, or 50:50 (mole-to-mole) mixture of MgCl.sub.2 and KCl salts, or other suitable mixtures of molten salts known and used by those of ordinary skill in the art.

One-Pot System and Process

[0040] One or more embodiments of the present disclosure comprise a container, in a one-pot metal extraction and electrodeposition apparatus. The apparatus, or system, comprises: 1) a high temperature resistant, corrosion resistant outer crucible, wherein the outer crucible comprises non-porous glassy carbon material, or non-porous ceramic-filled graphite or quartz or a nonporous ceramic material; 2) a high temperature resistant, corrosion resistant inner crucible centered within a bottom of the outer crucible, wherein the inner crucible is cathodic (i.e. functions as a cathode in an electric circuit), and the inner crucible comprises porous graphite or non-porous glassy carbon material or a non-porous ceramic-filled graphite; 3) a molten salt within the inner crucible produced by combining a low melting aerated chloride salt and metal ore or slag; 4) an anode rod positioned vertically within the inner crucible; 5) a power supply operatively connected to the inner crucible cathode and the anode rod; and, 6) a means to stir for continuously mixing the molten salt and slag/ore within the inner crucible.

[0041] This one-pot method has been tested for copper extraction and electrodeposition but should work for any metal whose formal reduction potential is more positive than the reduction potential of the most noble metal ion in a molten chloride salt (for example, in NaCl KCl ZnCl.sub.2, it is the reduction potential of zinc, which is 0.76 V versus NHE) and less than the reduction potential of oxygen, the most aggressive oxidant in air, whose reduction potential is 1.2 V versus NHE. Clearly desirable metals can be processed including gold, silver, nickel, etc.

Multi-Crucible System and Process

[0042] Various embodiments of the present disclosure also comprise environmentally friendly processes for extracting and depositing metals from ore and/or slag, while using a plurality of crucibles, vessels, reactors, containers, etc. The multi-crucible system and process is suitable for full scale manufacturing operations that extract and deposit large quantities of metal from ore and/or slag.

[0043] The various embodiments of the multi-crucible system comprise the following components: a mixing crucible able to heat and dissolve metal in slag and/or ore that is aerobically mixed with a low vapor-pressure molten salts or ionic liquid; a mechanism to remove the undissolved slag or ore from the mixture (e.g. by filtration or decanting); an electro-chemical reactor able to conduct electro-deposition to remove the pure metal from the liquid solution by depositing it on a cathode electrode.

[0044] The electro-chemical reactor comprises: a high temperature resistant crucible storing the liquid solution; a cathode electrode and an anode electrode (e.g. graphite) connected to a direct current power supply on an upper end, and immersed in the liquid solution on a bottom end; and, one or more valves to drain the electrified liquid solution from the reactor crucible and into a movable re-cycle tank.

[0045] The movable re-cycle tank is able to first receive dense metal (e.g. copper) and then be replaced by an empty tank for receiving the metal-depleted electrified liquid solution comprising molten salts or ionic liquid, which can then be used to transport the electrified liquid salt solution back to the mixing crucible and/or a heat exchanger unit. In an embodiment, the re-cycle tank is heat and liquid sealed to prevent significant loss of heat and the used liquid solution.

Heat Recycling

[0046] In an embodiment of the invention, it is also possible to recycle heat using the chlorides as the molten chloride salts being used to extract and plate copper were originally developed at the University of Arizona as heat transfer fluids for concentrating solar power for electrical power generation. During the copper making process which occurs in molten chloride salt, copper-depleted, deoxygenated and dehydrated molten chloride salt or fresh deoxygenated and dehydrated molten chloride salt can be stored in a tank and passed through pipes where heaps of hot ground copper earth, concentrates or slag are stored in order to extract heat from the heaps. The salt needs to be deoxygenated and dehydrated only if metal tanks and pipes are used. For example if graphite, or clay filled graphite, pipes and containers are used, the salt need not be deoxygenated and dehydrated.

[0047] One scenario illustrating the use of the heat exchanger is the fact that can be extracted from a slag heap piled into a closed bucket with a heat collecting tube containing molten salt and passing through the hot slag heap. Collecting heat into the collecting tube is just like the heat collecting tube used to collect heat from sun shining on a pipe containing molten salt in a plant for concentrating solar power. The slag can stay in the bucket until most of the usable heat is sent into the molten salt to make electricity. That is, the freshly heated molten salt can go to a heat exchanger, in a steam generator, to make steam to, in turn, make electricity for electroplating copper or for providing electrical power in the plant or even nearby residential housing. Instead of sending the heated molten salt to the steam generator, the heated molten salt can fill a graphite kettle which is used to process slag or ore.

[0048] The molten salt in the slag or ore is used to dissolve metals in the molten salt, and after metal ions are dissolved, the metal ions are electroplated at temperatures over the melting point of metal (e.g., 1,984 F. or 1,085 C. for copper), causing the liquid metal sinks to the bottom of the kettle, which can then be poured out of the kettle by means of a drain. When most of the desired heat is transferred from the slag to the salt for whatever reason, then the slag can be dropped into the graphite kettle by opening the bottom of the bucket so slag passes through the pipe into the graphite kettle for processing into copper metal and then new hot slag is put into the bucket and the whole process is started again.

[0049] Any heat not used to make electricity for making copper ions to copper metal can be used to make electricity for factories and houses in nearby areas. Two hundred and fifty (250) megawatts is enough electricity for 70,000 households. So the huge amounts of waste heat in copper heaps can be used to make commercial amounts of electricity. Any of the heat in the molten salt which is not extracted from the heat exchanger can be stored as hot salt in tanks and the stored energy can be extracted for heating the smelter process(s) or sent to a steam generator for making electricity on demand.

DETAILED DESCRIPTION OF THE DRAWINGS

[0050] The present invention is further illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in parentheses in the following detailed description.

[0051] Referring to FIG. 1, there is shown a schematic drawing of one embodiment of the system and process of the present disclosure. Metal ore and/or slag 110 (e.g. comprising copper, gold, silver, or any combinations thereof) is added to and stirred in crucible 120 which contains high temperature, molten salt (MS) or ionic liquid (IL) recycled from tank 150. The crucible 120 is exposed to air, meaning that the top of the crucible remains uncovered, or that air is stirred into the liquid solution. In an embodiment, the molten salt comprises sodium chloride and potassium chloride and zinc chloride eutectic (i.e. NaCL-KClZnCl.sub.2), in a mixture of a 0.5 to 0.5 to 1 molar ratio, respectively. This NaClKClZnCl.sub.2 molten salt melts at about 200 C. and has very low vapor pressure (7 psig) and is chemically stable to over 1000 C. in air.

[0052] The ore or slag is added to crucible 120 via standard machinery known in the art, such as via a crane or conveyer belt. The re-used molten salts or ionic liquids may be pumped or poured into the crucible 120 from the re-cycle tank 150.

[0053] Heat is applied to the crucible 120 while the metal from ore or slag is dissolved into the molten salt or into the ionic liquid, and the mixture is stirred to dissolve the metal ore or slag. This will produce a liquid solution containing a metal chloride (e.g. CuCl.sub.2). The appropriate temperature range for the applied heat is about five hundred to eleven hundred degrees Celsius, although other temperatures are envisioned within the scope of the present disclosure and are a function of the type of molten salt or ionic liquid used and the metal being extracted. The source of the heat 130 may be melted slag from ore smelters (e.g. up to 1650 degrees Celsius) and/or standard heat generating electro-mechanical devices known by one of skill in the art.

[0054] In one embodiment (as shown in FIG. 1), the liquid solution is passed through a filter 140 by gravity or a vacuum pump 170. Excess slag residue is discarded by inverting the crucible by using, e.g., a crane or other mechanical method. The remaining solution enters a crucible 106 which is subjected to heat via source 132. Crucible 106 comprises a pair of electrodes 108 (anode) and 109 (cathode). Crucible 106 further comprises a pressure release mechanism 105 as a safety mechanism for when the pressure becomes too high within the crucible. Crucible 106 further comprises a valve 107 to first drain the molten metal into a recycling tank 150 and then to drain the used metal depleted molten salt or ionic liquid into the tank 150. The used, heated molten salt in the recycling tank is then transported back to and added into the stirring crucible 120, via for example the use of a crane. One of skill in the art would readily know of mechanisms to transfer used molten salt or ionic liquid from tank 150 to crucible 120 (e.g. automated rail movement, vehicle operated by driver, etc.). Thus the hot molten salt is re-cycled to reduce operating cost for materials and for heating.

[0055] During the metal plating step a variety of types of electrodes 108, 109 can be used, (e.g. graphite, glassy carbon, or any stable refractory metal). Metal forms on graphite cathode 109. As metal forms on the cathode 109, the graphite anode 108 will oxidize to carbon dioxide due to the presence of trace water in the molten salt in contact with air.

[0056] Referring to FIG. 2, there is shown a summary of the general steps of the metal leaching process using low vapor pressure, aerated molten salts or ionic liquids of the various embodiments disclosed herein, and FIG. 3 is one exemplary embodiment of FIG. 2. The vessel further comprises a bottom and walls extending upward from said bottom. The opening formed by the top of the vessel walls is exposed to air, and the vessel is optionally configured with a mechanical stirrer. In operation, the mixture of molten electrolyte and metal-ion rich material is stirred to aerate the mixture of molten electrolyte salt and metal-ion rich material, thereby causing metal ions to dissolve in the electrolyte.

[0057] In step 210, the metal ore or slag is mixed with the low vapor-pressure molten salt or ionic liquid to form a mixture. The mixture is aerated, via for example having the crucible not be covered. The crucible is temperature controlled to enable all metal and metal oxides to be extracted from the ore or slag, and to form metal ions which are dissolved in the liquid solution in the mixture.

[0058] In step 220, the liquid solution with the metal ions is separated from the metal depleted solid ore or slag by filtration or decanting (pouring off from a level just above the metal depleted solid), or other industrial separation process. The metal depleted solid can be dumped at this point, for example by inverting the vessel, which can then be reused to transfer heat to a new liquid solution of metal rich ore or slag and molten salts or ionic liquid.

[0059] In step 230, the metal-rich hot liquid solution is put into an electrochemical reactor for electrodeposition. At this step the very hot liquid (about or above 1000 C.) can be passed in a metal tube from the pot (heat exchanger to a water bath) and the cooled (500 C.) liquid back to a graphite pot which acts as a cathode to make metal. The exchanged heat can be used to make steam from water to drive a turbine generator to make electricity.

[0060] In step 240, metal ions from the liquid solution are electrodeposited as pure metal at a carbon cathode while carbon dioxide forms at a carbon anode using an electrical current.

[0061] The metal is denser than the salt and can be poured out from the bottom of the reaction vessel (like a graphite crucible) while metal-depleted low vapor-pressure liquid remaining on top in the electrochemical reactor may then be recycled to the initial step for again extracting metal from ore or slag.

[0062] Referring now to FIG. 3, there is shown a schematic chart of an exemplary embodiment of a method and system for extracting metal ion into molten salt (e.g. leaching metals from slags using molten salts). The heat from the hot melted slag 305 passes through a heat exchanger 315. The heat exchanger 315 provides heat to the molten salt and this last hot salt is stored in an isolated tank 320. The melted slag 305 that passes through the heat exchanger 315 goes to a granulator 330; where in the granulator 330 are produced small particles of slag. The particles of slag are mixed with the molten salt; then slag and molten salt are stirred in a tank 340. Separation of molten salt and the slag residues is carried out by decanting or filtration 350. The aerobic molten salt produced during the stirring process dissolves metal ions and the ions are reduced and electrodeposited as metals layers on graphite electrodes 360, wherein the metals are recovered from the graphite. After electrodeposition of the metals, the molten salt is released of metal ions and it is deposited in a tank 370, and now it is ready to be recycled. The recycled molten salt goes to the initial heat exchanger 315 to be heated again and used as a heat transfer fluid.

[0063] FIG. 4 shows a schematic diagram of an exemplary production plant system 400 for extracting metal ions from ore or slag using molten salt based upon the process and system of FIGS. 2 and 3. The plant can be scaled to various sizes by one of skill in the art.

[0064] In tank 405 the melted slag is separated from the ore smelter, and it passes through a heat exchanger 410 where the molten slag provides thermal energy to the recycled molten salt dropping from shaft 475 past the heat exchanger 410 to tank 420. The molten slag decreases its temperature due to the heat exchanger and goes to a granulation process where small particles are obtained at tank 415. All of the molten salt that is recycled is deposited in a heat insulation tank 420 where it can be mixed with fresh salts for recovering of the salt wasted in the process. From the heat insulation tank 420 is taken molten salt and it is mixed at tank 425 with the slag that comes from the granulator system 415. The mixture is maintained under stirring via device 430 for some time until it reaches the thermodynamic equilibrium. In this part of the process the metal ions are extracted into the molten salt.

[0065] For separation of the molten salt that contains metal ions from the residual slag, the stirring is stopped and after waiting some time the precipitation of the residual slag is carried out; the residual slag goes to the bottom of the tank at 435. In the bottom of the tank at 435 is a gate that is opened for decanting or filtration of the molten salt. In the separation process the residual slag is taken out using a circular arm and the molten salt passes over the slag or through a filter 440. The stirring process keeps a constant temperature by using molten salt that comes from the heat insulation tank.

[0066] After separating the molten salt from slag, the molten salt goes to a container 455 with two graphite electrodes at 450 where the metal ions are separated from the molten salt by electrodeposition of metal on a graphite electrode. As metal forms at the graphite cathode, on the anode the graphite will oxidize to carbon dioxide, due to anodic current and the presence of trace water in the molten salt in contact with air. The water ultimately comes from the air. The container where the electrodeposition is carried out is maintained at elevated temperature (greater than 400 degrees Celsius) using heat exchanged from the molten salt that came from the heat insulation tank 420 at pipe opening 460. When almost all of the metal ions are separated from the molten salt by electrodeposition, a gate is open and the metal depleted molten salt is poured into a second heat insulation tank 470 or piped in via pipes 465. From this second insulation tank 470, the molten salt is recycled to the heat exchanger via piping to opening 475 and/or by using a mobile container in order to be heated again at the heat exchanger 410.

[0067] It is recognized that the system illustrated in FIG. 4 is one exemplary embodiment, and that one of skill in the art could readily modify the schematic to arrive at an equivalent system of a large scale facility for extracting metal from melted slag.

[0068] The terms plurality may be used throughout the specification to describe two or more components, devices, elements, units, parameters, or the like. Unless explicitly stated, the method embodiments described herein are not constrained to a particular order or sequence. Additionally, some of the described method embodiments or elements thereof can occur or be performed at the same point in time.

[0069] Although various features of the present disclosure may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the various embodiments may be described herein in the context of separate embodiments for clarity, they may also be implemented in a single embodiment. It is to be understood that the phraseology and terminology employed herein is not to be construed as limiting and are for descriptive purpose only. It is to be understood that the details set forth herein do not construe a limitation to an application of the various embodiments.