Method for thiosulfate-based electrochemical leaching-recycling integrated short-process extraction of precious metal

Abstract

Disclosed in the present invention is a method for thiosulfate-based electrochemical leaching-recycling integrated short-process extraction of a precious metal. The method comprises: dissolving a thiosulfate and an electrolyte, then adding an alkali liquor thereto, and stirring same until uniform to obtain an electrolyte solution, wherein the electrolyte is a salt which does not contain a thiosulfate; adjusting the pH value of the electrolyte solution to 7-13, then placing the electrolyte solution and a material containing a precious metal into an electrolytic bath, and performing an electrolysis operation using an electrode system arranged in the electrolytic bath so as to achieve the leaching of the precious metal at an anode and the deposition thereof at a cathode, the voltage of the electrolysis operation being 0.1-3 V; and collecting the elemental precious metal deposited on the cathode. The present invention can achieve both the leaching of a precious metal at an anode and the electrolytic deposition of precious metal ions at a cathode in one reaction device, realizes integrated extraction of a precious metal by means of synchronous leaching and recycling, and has the advantages of high extraction efficiency, a short technological process, low reagent consumption, low energy consumption, no pollution, etc.

Description

A method for extracting precious metals by integrating thiosulfate electrochemical leaching and recovery into a short process Technical Field

[0001] The present invention belongs to the technical field of hydrometallurgy, and in particular relates to a method for extracting precious metals through an integrated short-process of thiosulfate electrochemical leaching and recovery. Background Art

[0002] Precious metals are strategic mineral resources crucial for safeguarding national economic and financial security. Currently, there are two main extraction methods: pyrometallurgical and hydrometallurgical. Wet leaching has been widely studied due to its low-carbon, environmentally friendly, and energy-efficient advantages. The leaching reaction is essentially a redox reaction, whereby the precious metal loses electrons and is oxidized to precious metal ions, which enter the solution. The enriched precious metal ions then gain electrons and are reduced to their elemental form for recovery. The current wet leaching process involves leaching precious metal-containing materials with leaching agents such as cyanide, thiosulfate, or thiourea. The precious metal coordination ions in the leachate are then adsorbed by activated carbon or resin, and then desorbed onto the gold-loaded carbon or resin to produce a precious solution. Finally, the precious metal coordination ions in the precious solution are reduced to the elemental precious metal through displacement or electrolysis. In existing processes, the oxidation leaching of the precious metal material and the reduction and recovery of the precious metal coordination ions are independent of each other, making the entire wet leaching process complex and leading to long precious metal leaching cycles, low efficiency, and high costs.

[0003] Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a method for extracting precious metals by integrating thiosulfate electrochemical leaching and recovery into a short process, so as to solve the problems of the current precious metal wet leaching process, such as complex process flow, long extraction cycle, low efficiency and high cost.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A method for extracting precious metals by integrating thiosulfate electrochemical leaching and recovery into a short process comprises the following steps:

[0007] S1: dissolving thiosulfate and electrolyte, adding alkaline solution, and stirring evenly to obtain an electrolyte; the electrolyte is a salt that does not contain thiosulfate;

[0008] S2: Adjusting the pH of the electrolyte to 7-13, placing the electrolyte and the precious metal-containing material in an electrolytic cell, and performing electrolysis using an electrode system within the electrolytic cell such that the precious metal is leached at the anode and deposited at the cathode; the voltage of the electrolytic operation is 0.1-3V;

[0009] S3: Collect the precious metal elements deposited on the cathode.

[0010] Preferably, the concentration of thiosulfate in the electrolyte is 0.1-0.5M, the concentration of electrolyte is 0.1-0.5M, and the concentration of alkali solution is 0.3-1.5M.

[0011] Preferably, the concentration of thiosulfate in the electrolyte is 0.2-0.3M, and the concentration of electrolyte is 0.3-0.4M.

[0012] Preferably, in step S2, the pH of the electrolyte is adjusted to 10-11.

[0013] Preferably, the thiosulfate is one or more of sodium thiosulfate, ammonium thiosulfate, and potassium thiosulfate; and the alkali solution is one or more of ammonia water, sodium hydroxide, and potassium hydroxide.

[0014] Preferably, the electrolyte is one or two of chloride, sulfate and carbonate.

[0015] Preferably, the material containing precious metals is pure gold sheet, silver sheet or waste circuit board.

[0016] Preferably, the cathode of the electrolysis system is a titanium plate or a copper plate, and the anode is one of platinum, titanium, copper, lead, glassy carbon, silicon carbide, stainless steel, graphite electrode, and graphite felt.

[0017] Preferably, a diaphragm is provided in the electrolytic cell, and the diaphragm divides the electrolytic cell into a cathode chamber and an anode chamber.

[0018] Preferably, the diaphragm is 600-800 mesh acid and alkali resistant filter cloth or nylon mesh.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention realizes a short process of extracting precious metals by integrating thiosulfate electrochemical leaching and recovery, i.e., anodic oxidation leaching and cathode reduction occur simultaneously. Within 24 hours, the gold leaching rate is 100% and the recovery rate is 99.8%;

[0021] 2. The present invention greatly shortens the extraction time. Compared with the traditional extraction process, the extraction time of precious metals is shortened from 65h to 24h;

[0022] 3. The present invention simplifies the precious metal extraction process steps, has the advantages of high efficiency, low energy consumption, short flow path, and no pollution, and can achieve efficient and green one-step extraction of precious metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a schematic diagram of a conventional process for extracting precious metals;

[0024] FIG2 is a schematic diagram of the electrochemical leaching-recovery integrated precious metal extraction process of the present invention;

[0025] FIG3 is a diagram showing the effect of extracting precious metals in one step of leaching and recovery in Example 1;

[0026] FIG4 is a diagram showing the effect of integrated leaching and recovery of gold from PCBs in Example 2;

[0027] Figure 5 shows different S2O3 2- The effect of concentration on the integrated extraction of gold from PCBs by leaching and recovery;

[0028] FIG6 is a diagram showing the integrated extraction effect of leaching and recovery of gold from PCBs at different KCl concentrations;

[0029] Figure 7 is a diagram showing the effects of different initial pH on the integrated leaching and recovery of gold from PCBs. DETAILED DESCRIPTION

[0030] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0031] As shown in Figure 1, when copper ammonia-thiosulfate is used to leach gold, the leachate after solid-liquid separation needs to be processed through adsorption, desorption, reduction and other processes to recover precious metals. The traditional process has problems such as low efficiency, high reagent consumption, high cost and long time consumption.

[0032] Based on this, the present invention creatively proposes a method for extracting precious metals by integrating thiosulfate electrochemical leaching and recovery in a short process. The precious metals are dissolved by electrochemical anodic oxidation at a low voltage, and the reduction and recovery of the leachate are effectively combined with the cathode. The integrated reaction of anode mineral metal leaching and cathode leachate electrolytic deposition can be realized in one reaction device, achieving an integrated extraction effect of leaching and recovery. It has the advantages of high extraction efficiency, short process flow, low reagent consumption, low energy consumption, and no pollution, making the metal extraction process safer and more cost-effective. Specifically, the method for extracting precious metals by integrating thiosulfate electrochemical leaching and recovery in a short process provided by the present invention is shown in Figure 2 and comprises the following steps:

[0033] S1: Prepare an electrolyte: Dissolve thiosulfate and chloride, add alkali solution, and stir evenly to obtain an electrolyte; the concentration of thiosulfate in the electrolyte is 0.1-0.5M, preferably 0.2-0.3M; the concentration of the electrolyte is 0.1-0.5M, preferably 0.3-0.4M; the concentration of the alkali solution is 0.3-1.5M. The type of thiosulfate is not limited, and can be one or more of sodium thiosulfate, ammonium thiosulfate, and potassium thiosulfate; the type of alkali solution is not limited, and can include but is not limited to one or more of ammonia, sodium hydroxide, and potassium hydroxide; the electrolyte is a salt that does not contain thiosulfate, for example, can be one or two of chloride, sulfate, and carbonate.

[0034] S2: Adjust the pH of the electrolyte to 7-13, preferably 10-11; then place the electrolyte and the material containing precious metals in an electrolytic cell, and use the electrode system provided in the electrolytic cell to perform electrolysis so that the precious metals are leached at the anode and deposited at the cathode; the voltage of the electrolysis operation is 0.1-3V; the material containing precious metals can be pure gold sheets, silver sheets or discarded circuit boards. The cathode of the electrolytic system is a metal electrode with good conductivity such as a titanium plate or a copper plate, which needs to be polished before use, and the anode is an electrode material with good conductivity such as platinum, titanium, copper, lead, glassy carbon, silicon carbide, stainless steel, graphite electrode and graphite felt. Preferably, a diaphragm is provided in the electrolytic cell, which divides the electrolytic cell into a cathode chamber and an anode chamber. The diaphragm can be a 600-800 mesh acid and alkali resistant filter cloth or nylon mesh to prevent solid minerals or impurities in the anode chamber from entering the cathode.

[0035] S3: Collect the precious metal elements deposited on the cathode.

[0036] The present invention is a novel thiosulfate electrochemical oxidation system (S2O3 2- - electrolyte - alkali solution) can achieve the reduction of cathode metal ions during anodic oxidation leaching. The reaction of precious metal wet leaching is essentially a redox reaction, that is, the precious metal loses electrons and is oxidized to precious metal ions. In the anodic process, the metal mineral collides with the anode and loses electrons to undergo electrochemical oxidation and reacts with S2O3 2- Complexation is achieved to leaching, the leached Au(S2O3 2- )2 3- Under the action of concentration diffusion and convection, it reaches the cathode, where it receives electrons and undergoes reduction, thereby achieving leaching and recovery. In the present invention, thiosulfate is a leaching complexing agent, and the presence of alkali solution (such as ammonia water) can prevent the insoluble products of thiosulfate from precipitating on the gold surface during the dissolution process, such as elemental sulfur. When the alkali solution is ammonia water, the complex M(S2O3)(NH)3 - The formation of can prevent the oxidation / disproportionation of unstable thiosulfate. The reaction formula is as follows:

[0037] Anode: Au+2S2O32- -e - =Au(S2O3 2- )2 3-

[0038] Cathode: Au(S2O3 2- )2 3- +e - =Au 0 +2S2O3 2-

[0039] The present invention is described in detail below with reference to specific embodiments.

[0040] The calculation formulas for the leaching rate and recovery rate of precious metals in the present invention are as follows:

[0041] Example 1

[0042] The electrolyte composition is 0.2M Na2S2O3, 0.2M KCl, 0.5M NH3, and is adjusted to pH0=10 with sodium hydroxide.

[0043] S2O3 2- A KCl-NH₃ system reaction electrolyte was poured into a cylindrical electrolytic cell. The anode was a pure mineral gold sheet, and the cathode was a titanium plate of the same size as the anode. A DC power supply was connected, the voltage was adjusted to 0.6V, and the rotation speed was adjusted to 500rpm. Samples were taken at different times, and the gold concentration in the electrolytic cell was measured by atomic absorption spectroscopy at different time points. After 24 hours, the anode and cathode plates were collected, cleaned, and dried. The quality of the anode and cathode plates before and after the reaction was compared, and the cathode plate morphology was photographed using a scanning electron microscope. The electrochemical oxidation leaching and electrodeposition reduction effects were evaluated based on the gold concentration in the solution and the SEM image of the cathode. The experimental results are shown in Figure 3. As shown in Figure 3(A), the gold concentration in the solution remained at approximately 63 mg / L from 10 hours to 24 hours. Figure 3(B) shows that the titanium plate at the cathode changed from silver to a smooth golden yellow, with a large amount of gold deposited on it. This indicates that while the gold sheet leached at the anode, the cathode also played a reducing role. Gold leaching and reduction can be achieved in the same system and device.

[0044] Example 2

[0045] A thiosulfate electrochemical leaching-recovery integrated method for extracting gold from PCBs comprises the following steps:

[0046] The electrolyte composition is 0.2M Na2S2O3, 0.3M KCl, 0.5M NH3, and is adjusted to pH0=10 with sodium hydroxide.

[0047] The middle of the electrolytic cell is separated by 600 mesh nylon mesh to prevent PCBs solid minerals from entering the cathode and to divide the electrolytic cell into anode and cathode chambers. 2- A KCl-NH3 reaction electrolyte was poured into the anode and cathode chambers of the electrolytic cell, maintaining the liquid levels level. A PCB powder sample was placed in the anode chamber, connected to the cathode and cathode electrodes: a graphite felt (GF) anode and a titanium plate of the same size as the anode. The rotation speed was adjusted to 800 rpm, and a DC power supply was connected to a voltage of 0.6 V before the reaction was carried out. After the reaction, the solid slag from the anode chamber was collected for gold content, and the cathode plate was collected, dried, and weighed to calculate the leaching rate and recovery rate. The experimental results are shown in Figure 4. Under this system, the gold leaching rate was 100% and the recovery rate was 99.8%.

[0048] Example 3

[0049] A thiosulfate electrochemical leaching-recovery integrated extraction of gold from PCBs (different S2O3 2- concentration)

[0050] Prepare 5 different S2O3 2- Concentration of S2O3 2- -KCl-NH3 system reaction electrolyte, S2O3 2- The concentrations are 0.1, 0.2, 0.3, 0.4, and 0.5 M respectively, and the other reagents are 0.3 M KCl and 0.5 M NH3 respectively. The pH of the electrolyte is 0=10.

[0051] The middle of the electrolytic cell is separated by a 600-mesh nylon mesh to prevent PCBs solid minerals from entering the cathode, and the electrolytic cell is divided into anode and cathode chambers. The prepared electrolyte is poured into 5 electrolytic cells respectively, and the liquid levels of the anode and cathode chambers are kept level. The same mass of PCBs powder samples are placed in the anode chamber respectively, and the anode and cathode electrodes are connected. The anode is GF and the cathode is a titanium plate of the same size as the anode. The speed is adjusted to 800rpm, and a DC power supply is connected. The voltage is adjusted to 0.6V and the reaction is carried out. After the reaction is completed, the solid slag in the anode chamber is collected to measure the gold content, and the cathode plate is collected for drying and weighing. The leaching rate and recovery rate are calculated. The experimental results are shown in Figure 5. It can be seen that different S2O3 2- Concentration has a certain influence on leaching rate and recovery rate. When S2O3 2- The best effect was achieved when the concentration was 0.3 M, with a gold leaching rate of 100% and a recovery rate of 100%.

[0052] Example 4

[0053] A thiosulfate electrochemical leaching-recovery integrated extraction method for gold from PCBs (different KCl concentrations)

[0054] Prepare 5 S2O3 solutions with different KCl concentrations2- -KCl-NH3 system reaction electrolyte, KCl concentrations are 0.1, 0.2, 0.3, 0.5, 0.7, and the other reagents are 0.2M S2O3 2- , 0.5M NH3, pH of the electrolyte is 0=10.

[0055] The electrolytic cell was separated by a 600-mesh nylon mesh to prevent solid PCBs from entering the cathode. The cell was then divided into anode and cathode chambers. The prepared electrolyte was poured into each of the five electrolytic cells, maintaining the liquid levels in the anode and cathode chambers at equal levels. Identical PCB powder samples were placed in the anode chamber, and the anode and cathode electrodes were connected. The anode was a GF and the cathode was a titanium plate of the same size. The rotation speed was adjusted to 800 rpm. A DC power supply was connected and the voltage was adjusted to 0.6 V before the reaction was allowed to proceed. After the reaction, the solid slag from the anode chamber was collected for gold content, and the cathode plate was collected, dried, and weighed. The leaching rate and recovery rate were calculated. The experimental results are shown in Figure 6. Different KCl concentrations significantly affected the leaching rate and recovery rate. The optimal leaching-recovery performance was achieved at a KCl concentration of 0.3 M, with a gold leaching rate of 100% and a recovery rate of 99.8%.

[0056] Example 5

[0057] A thiosulfate electrochemical leaching-recovery integrated extraction method for gold from PCBs (different pH values)

[0058] Preparation of 6 S2O3 with different initial pH 2- -KCl-NH3 system reaction electrolyte, initial pH is 7, 8, 9, 10, 11, 12, and the other reagents are 0.2M S2O3 2- , 0.3M KCl, 0.5M NH3

[0059] The electrolytic cell was separated by a 600-mesh nylon mesh to prevent solid PCB minerals from entering the cathode. The cell was then divided into anode and cathode chambers. The prepared electrolyte was poured into each of the six electrolytic cells, maintaining the liquid levels in the anode and cathode chambers at the same level. Equal masses of PCB powder samples were placed in the anode chambers. The anode and cathode electrodes were connected, with a GF anode and a titanium plate of the same size as the anode. The rotation speed was adjusted to 800 rpm, and a DC power supply was connected at a voltage of 0.6 V before the reaction was carried out. After the reaction, the solid slag in the anode chamber was collected for gold content, and the cathode plate was collected, dried, and weighed. The leaching rate and recovery rate were calculated. The experimental results are shown in Figure 7. Different pH values ​​significantly affected the leaching rate and recovery rate, with the optimal recovery rate achieved at pH = 10.

[0060] It should be noted that the above embodiments all belong to the same inventive concept, and the description of each embodiment has its own focus. For any details not described in individual embodiments, reference may be made to the description in other embodiments.

[0061] The above-described embodiments merely illustrate the implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for integrated short - process extraction of precious metals by thiosulfate electrochemical leaching - recovery, characterized in that, The steps include: S1: dissolving thiosulfate and electrolyte, adding alkali solution, and stirring evenly to obtain an electrolyte; the electrolyte is a salt that does not contain thiosulfate; S2: adjusting the pH of the electrolyte to 7-13, then placing the electrolyte and the material containing the precious metal in an electrolytic cell, and performing electrolysis using an electrode system disposed in the electrolytic cell, so that the precious metal is leached at the anode and deposited at the cathode; the voltage of the electrolysis operation is 0.1-3V; S3: Collect the precious metal element deposited on the cathode.

2. The method for integrally and short - process extracting noble metals by thiosulfate electrochemical leaching - recovery according to claim 1, characterized in that The concentration of thiosulfate in the electrolyte is 0.1-0.5M, the concentration of the electrolyte is 0.1-0.5M, and the concentration of the alkali solution is 0.3-1.5M.

3. The method for integrative short - process extraction of precious metals by thiosulfate electro - chemical leaching - recovery according to claim 2, wherein, The concentration of thiosulfate in the electrolyte is 0.2-0.3M, and the concentration of the electrolyte is 0.3-0.4M.

4. The method for integrative short - process extraction of precious metals by thiosulfate electrochemical leaching - recovery, according to claim 1, is characterized in that, In step S2, the pH of the electrolyte is adjusted to 10-11.

5. The method for integrally and short - process extracting noble metals by thiosulfate electrochemical leaching - recovery, according to claim 1, is characterized in that The thiosulfate is one or more of sodium thiosulfate, ammonium thiosulfate, and potassium thiosulfate; the alkali solution is one or more of ammonia water, sodium hydroxide, and potassium hydroxide.

6. The method for integrally and short - process extracting noble metals by thiosulfate electrochemical leaching - recovery according to claim 1, characterized in that, The electrolyte is one or two of chloride, sulfate and carbonate.

7. The method for integrative short - process extraction of precious metals by thiosulfate electro - chemical leaching - recovery according to claim 1, wherein, The material containing precious metals is pure gold sheet, silver sheet or waste circuit board.

8. The method for short - process extraction and recovery of precious metals by thiosulfate electro - chemical leaching - recovery integration according to claim 1, characterized in that, The cathode of the electrolysis system is a titanium plate or a copper plate, and the anode is one of platinum, titanium, copper, lead, glassy carbon, silicon carbide, stainless steel, graphite electrode, and graphite felt.

9. The method for integrative short-process extraction of precious metals by thiosulfate electrochemistry leaching and recovery according to claim 1, wherein, A diaphragm is arranged in the electrolytic cell, and the diaphragm divides the electrolytic cell into a cathode chamber and an anode chamber.

10. The method for integrated short - process extraction of precious metals by thiosulfate electro - chemical leaching - recovery, according to claim 9, is characterized in that, The diaphragm is 600-800 mesh acid and alkali resistant filter cloth or nylon mesh.

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