Anode recovery method for precious metal in thiosulfate solution

Abstract

The invention discloses an anode recovery method for precious metals in a thiosulfate solution. The anode recovery method comprises the following steps: respectively preparing an electrolyte solution and a thiosulfate solution containing chloride ions; a cation exchange membrane is arranged in the electrolytic cell, and the electrolytic cell is divided into an anode chamber and a cathode chamber by the cation exchange membrane; and placing the thiosulfate solution containing the chloride ions in an anode chamber, placing the electrolyte solution in a cathode chamber, carrying out electrolysis operation by using an electrode system arranged in the electrolytic bath, and recovering the noble metal deposited on the anode. According to the method, one-step reduction and recovery of noble metal coordination ions at the anode can be achieved under the low-voltage condition, the recovery rate of the noble metal reaches up to 99.8%, codeposition of the noble metal and other metals at the cathode at the same time is avoided, and the grade of the noble metal is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of precious metal recovery, and in particular relates to an anode recovery method for precious metals in a thiosulfate solution. Background Art

[0002] The thiosulfate method for extracting precious metals is a joint action of thiosulfate and oxidant to dissolve the precious metal element into coordination ions, which generally occurs in the presence of oxygen. In order to speed up the leaching rate, researchers introduced copper as an oxidant and ammonia as a stabilizer to form a copper-ammonia-thiosulfate leaching system, from which other thiosulfate leaching systems such as copper-amine, nickel-ammonia, cobalt-ammonia, and copper-citrate have also been derived. The thiosulfate method is non-toxic, has high leaching efficiency, and is cost-effective. It is in line with the global green development goals and has the greatest industrial application potential in cyanide-free gold extraction technology. However, the technical difficulty of recovering precious metal coordination ions restricts the practical application of this technology.

[0003] At present, the mainstream technologies for recovering noble metal coordination ions are replacement, adsorption, extraction, and electrodeposition. The replacement method can obtain noble metal elements, but other metal ions in the solution are easily precipitated simultaneously, resulting in low product purity. The adsorption method has a simple process, but it can only enrich ions, and subsequent reduction treatment is still required to obtain the element, and there are disadvantages such as severe competitive adsorption and low adsorption efficiency in the process. The solvent extraction method can also only extract and enrich ions, and is only applicable to high-concentration solutions, and the cost of reagents is high. The electrodeposition method has a mature process, a simple flow, and no chemical additives. It has become the dominant technology for recovering elemental metals from leachates. Although electrodeposition is often used as an important part of the back-end reduction process in industry, there are still some key problems in practical applications: the applicable object of electrodeposition is usually concentrated noble solution. When the concentration of noble metals is lower than 130 mg / L, the current treatment efficiency of electrodeposition is lower than 15%; in addition, a large number of base metal ions in the leachate will be simultaneously precipitated at the cathode, which reduces the grade and deposition efficiency of the noble metals.

[0004] Therefore, the present invention aims to develop an anode recovery method for precious metals in a thiosulfate solution to solve the above problems. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide an anode recovery method for precious metals in thiosulfate solution to solve the problems of high complex concentration requirements, low extraction efficiency, low precious metal grade, etc. when recovering precious metals from thiosulfate.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions: The present invention provides a method for recovering noble metals from an anode in a thiosulfate solution, comprising the following steps: preparing an electrolyte solution and a thiosulfate solution containing chloride ions respectively; A cation exchange membrane is arranged in the electrolytic cell, and the cation exchange membrane separates the electrolytic cell into an anode chamber and a cathode chamber; A thiosulfate solution containing chloride ions is placed in the anode chamber, an electrolyte solution is placed in the cathode chamber, and an electrolysis operation is performed using an electrode system arranged in the electrolytic cell to recover the precious metals deposited on the anode. Preferably, the molar ratio of thiosulfate ions to chloride ions in the thiosulfate solution containing chloride ions is (1:0.01)-(1:500).

[0007] Preferably, the concentration of the noble metal in the chloride ion-containing thiosulfate solution is 0.5-100 mg / L. The noble metal of the present invention includes gold and / or silver.

[0008] Preferably, the pH of the thiosulfate solution containing chloride ions is 6-11.

[0009] Preferably, the voltage of the electrolysis operation is 0.2-4 V; more preferably, it is 0.4-2.5 V.

[0010] Preferably, the concentration of the electrolyte solution is 0.5-500 mmol / L, and the pH is 3-12.

[0011] Preferably, the cathode and the anode of the electrolysis system are both electrode plates having an adsorption material layer on the surface.

[0012] Preferably, the material forming the adsorption material layer includes at least one of activated carbon, graphite, graphene, molybdenum disulfide, and cadmium sulfide.

[0013] Preferably, the adsorption material layer also includes a conductive material.

[0014] Preferably, the electrode plate is one of graphite felt, carbon felt, carbon cloth, carbon paper, titanium plate, and stainless steel plate.

[0015] The beneficial effects of the present invention are: The present invention proposes an anode recovery method for precious metals in thiosulfate solution. The biggest difference from the current mainstream electrodeposition technology (depositing metals on the cathode) is that this method does not require special operations or reagents, and can achieve one-step reduction and recovery of precious metal coordination ions at the anode under low voltage conditions. The precious metal recovery rate is as high as 99.8%, and it avoids the co-deposition of precious metals and other metals at the cathode at the same time, thereby improving the grade of precious metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is the recovery effect diagram of precious metals in Example 1 and Comparative Example 1; Figure 2It is the recovery effect diagram of precious metals in Example 2 and Comparative Example 2; Figure 3 It is a diagram of the recovery effect of precious metals in Examples 3~4 and Comparative Example 3. DETAILED DESCRIPTION

[0017] 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 described embodiments 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 creative work are within the scope of protection of the present invention.

[0018] The embodiment of the present invention provides a method for recovering noble metals from anodes in a thiosulfate solution, comprising the following steps: (1) Preparation of coated electrodes: Weigh the corresponding conductive materials and adsorbent materials according to the mass ratio of conductive material to adsorbent material of 1:1-1:50 and place them in an agate mortar, add a binder (such as vinylidene fluoride solution), and fully grind and mix all the materials. Among them, the conductive material includes but is not limited to conductive carbon black and acetylene black; the adsorbent material includes one or more of activated carbon, graphite, graphene, molybdenum disulfide, and cadmium sulfide. The mixed slurry is evenly coated on a clean conductive substrate (such as graphite felt, carbon felt, carbon cloth, carbon paper, titanium plate, stainless steel plate), dried, cooled to room temperature, and then soaked in pure water overnight to remove non-adherent materials, and then dried again for use.

[0019] (2) Preparation of precious metal solution: according to S2O3 2- :Cl - Prepare different concentrations of thiosulfate precious metal solutions (0.5-100 mg / L) in the range of molar ratio 1:0.01-1:500, and adjust the solution pH to 6-11. 2- The source can be one or more of ammonium thiosulfate, sodium thiosulfate, potassium thiosulfate, Cl - The source can be one or more of sodium chloride, potassium chloride, and ammonium chloride.

[0020] The molar ratio of thiosulfate ions to chloride ions in the chloride-containing thiosulfate solution is (1:0.01)-(1:500), preferably (1:0.5)-(1:410), and more preferably (1:2)-(1:300).

[0021] Specifically, the molar ratio of thiosulfate ions to chloride ions in the thiosulfate solution containing chloride ions is 1:0.01, 1:1, 1:20, 1:40, 1:60, 1:80, 1:100, 1:200, 1:300, 1:500 or any ratio within the above range.

[0022] (3) Preparation of electrolyte solution: Weigh a certain amount of inorganic salt and dissolve it in pure water to prepare an electrolyte solution with a concentration of 0.5-500mmol / L, and adjust the solution pH to 3-12 with saturated sodium hydroxide or hydrochloric acid. The inorganic salt includes but is not limited to one or more of sodium chloride, potassium chloride, ammonium chloride, sodium sulfate, potassium sulfate, ammonium sulfate, sodium sulfite, potassium sulfite, sodium thiosulfate, and ammonium thiosulfate.

[0023] (4) Anode recovery of precious metals: A two-chamber diaphragm electrolytic cell is used as the reaction container, in which the diaphragm is a cation exchange membrane. The two chambers of the electrolytic cell are respectively poured with precious metal solution and electrolyte solution. The side where the precious metal solution is placed is called the anode chamber, and the side where the electrolyte solution is placed is called the cathode chamber. The anode chamber is magnetically stirred at 50-1000 rpm. A pair of coated electrodes are placed in the cathode and anode chambers respectively, and a voltage of 0.2-4.0 V is applied by a DC power supply to start the anode recovery of precious metals. Among them, the applied voltage is preferably 0.4-2.5 V.

[0024] In some embodiments, the method for preparing the precious metal solution includes: weighing ammonium thiosulfate, adding water, and adding a standard solution of chloroauric acid dropwise, and controlling the pH value of the solution to 6-11 by adding saturated sodium hydroxide dropwise. In the process, since the standard solution of chloroauric acid required for preparing the solution uses 1.5 mol / L hydrochloric acid as a medium, a certain amount of Cl will be introduced into the solution when it is used to prepare the precious metal solution. - (1 mL of chloroauric acid contains 1.5 mmol Cl - On this basis, you can choose to adjust the Cl content of the solution by adding additional chloride salt. - content.

[0025] The present invention realizes the anode recovery of precious metals in thiosulfate solution, and the principle is: Under the action of the electric field, cations such as base metals (such as copper ions) in the thiosulfate leachate pass through the cation exchange membrane to leave the anode chamber, reducing the interference of high-concentration base metal ions in the anode chamber with low-concentration noble metal coordination ions. Because the noble metal coordination ions are negatively charged, they are trapped in the anode chamber by the cation exchange membrane; in addition, the chloride ions in the solution form a chloride ion adsorption layer at the anode interface, which is considered to be a specific reaction field, in which the noble metal coordination ions undergo a disproportionation reaction to form a single substance (as shown in Formula 1). Since the concentration of chloride ion reactants in the adsorption layer is very high and the thiosulfate product is oxidized and consumed at the anode, the disproportionation reaction is jointly promoted to occur in the forward direction. And the noble metal single substance can be protected from dissolution caused by anodic oxidation under the protection of the chloride ion layer. Therefore, the present invention can realize the selective recovery of noble metals in low-concentration thiosulfate solutions using anodes.

[0026] 3Au(S2O3)2 3- + mCl - + nOH - = 2Au + AuCl m (OH) n - + 6S2O3 2- (m+n=4) (1) The present invention is described in detail below with reference to specific embodiments.

[0027] Example 1 (1) Preparation of coated electrode: Weigh 5 mg of conductive carbon black and 40 mg of activated carbon into an agate mortar, add 0.4 mL of binder (prepared by dissolving 0.1 g of vinylidene fluoride in 8 mL of NN-dimethylacetamide), and grind and mix the materials thoroughly. Apply the mixed slurry evenly to a clean titanium plate and dry it in a 60°C oven. Take it out and cool it to room temperature, then soak it in pure water overnight to remove the unadhered material, and then dry it again for use.

[0028] (2) Preparation of precious metal solution: Preparation of S2O3 2- :Cl - A 15 mg / L noble metal solution with a molar ratio of 1:74 was prepared by weighing 6.7 mg of ammonium thiosulfate and adding it to 147 mL of water for dissolution, and then adding 2.25 mL of chloroauric acid standard solution (containing 3.375 mmol Cl - ), during which the solution pH was controlled to 10 by adding saturated sodium hydroxide to obtain 150 mL of precious metal solution.

[0029] (3) Preparation of electrolyte solution: Weigh 111.8 mg of potassium chloride and dissolve it in 149 mL of water. Adjust the pH of the solution to 7 with saturated sodium hydroxide to prepare 150 mL of 10 mmol / L electrolyte solution.

[0030] (4) Anode recovery of precious metals: A two-chamber diaphragm electrolytic cell is used as the reaction container, in which the diaphragm is a cation exchange membrane. The two chambers of the electrolytic cell are poured with precious metal solution and electrolyte solution respectively. The side where the precious metal solution is placed is called the anode chamber, and the side where the electrolyte solution is placed is called the cathode chamber. The anode chamber is magnetically stirred at 500 rpm. A pair of coated electrodes are placed in the cathode and anode chambers respectively, and a voltage of 1.2 V is applied through a DC power supply (the positive pole of the power supply is connected to the electrode in the precious metal solution), and the anode recovery test of precious metals is started. After the reaction is completed, the anode recovery rate of the precious metal is calculated, and the coating material on the anode after the reaction is characterized by XRD, such as Figure 1 shown.

[0031] from Figure 1It can be seen that the anode recovery rate of precious metals is 99.8%, and characteristic diffraction peaks belonging to gold element appear on the coating material of the anode, indicating that the precious metals in the solution are recovered on the anode in the form of elemental substances rather than adsorbed on the electrode in the form of ions.

[0032] Comparative Example 1 The precious metal recovery test was carried out using the same apparatus and method as in Example 1, except that a 0V voltage was applied to the test. Figure 1 As shown, the recovery rate of precious metals is only 1.1%, indicating that the activated carbon coating alone has almost no recovery effect on precious metals, which indicates that anode power supply is needed to achieve the recovery of precious metals from thiosulfate solution.

[0033] Example 2 (1) Preparation of coated electrode: According to the mass ratio of conductive material to adsorbent material of 1:9, 4 mg of conductive carbon black and 36 mg of activated carbon were weighed in an agate mortar, and 0.4 mL of binder (prepared by dissolving 0.1 g of vinylidene fluoride in 8 mL of NN-dimethylacetamide) was added. All materials were thoroughly ground and mixed. The mixed slurry was evenly coated on a clean titanium plate and dried in a 60°C oven. After cooling, it was soaked in pure water overnight to remove the unadhered materials, and then dried again for use.

[0034] (2) Preparation of precious metal solution: Preparation of S2O3 2- :Cl - A 5 mg / L noble metal solution with a molar ratio of 1:74 was prepared by weighing 2.25 mg of ammonium thiosulfate and adding it to 148.5 mL of water for dissolution, and then adding 0.75 mL of chloroauric acid standard solution (containing 1.13 mmol Cl - ), during which the solution pH was controlled to 10 by adding saturated sodium hydroxide to obtain 150 mL of precious metal solution.

[0035] (3) Preparation of electrolyte solution: Weigh 876.6 mg of sodium chloride and dissolve it in 149 mL of water. Adjust the pH of the solution to 5 with saturated sodium hydroxide to prepare 150 mL of 100 mmol / L electrolyte solution.

[0036] (4) Anode recovery of precious metals: A two-chamber diaphragm electrolytic cell is used as the reaction container, in which the diaphragm is a cation exchange membrane. The two chambers of the electrolytic cell are respectively poured with precious metal solution and electrolyte solution. The side where the precious metal solution is placed is called the anode chamber, and the side where the electrolyte solution is placed is called the cathode chamber. The anode chamber is magnetically stirred at 400 rpm. A pair of coated electrodes are placed in the cathode and cathode chambers of the electrolytic cell, respectively. A DC power supply is used to apply a voltage of 0.8 V (the positive pole of the power supply is connected to the electrode in the precious metal solution), and the precious metal anode recovery test is started. After the reaction is completed, the anode recovery rate of the precious metal is calculated, such as Figure 2 As shown, the anode recovery rate of precious metals is 98.5%, indicating that this method can achieve the recovery of precious metals in low-concentration solutions through the anode, the recovery rate increases with increasing voltage, and efficient recovery of precious metals at the anode can be achieved at only 0.8V.

[0037] Comparative Example 2 The same apparatus and method as in Example 2 were used to carry out the precious metal recovery test, except that 22.5, 225 and 2250 mg of ammonium thiosulfate were weighed to prepare three groups of S2O3 2- :Cl - Molar ratio of precious metal solution is 1:7.4, 1:0.74, 1:0.074. Figure 2 As shown in the figure, the anode recovery rates of the precious metals after the reaction were calculated to be 34.5%, 1.13%, and 0%, respectively. Compared with the experimental result of 98.5% recovery rate at 0.8V in Example 2, it was found that the S2O3 in the precious metal solution was increased at low voltage. 2- :Cl - The molar ratio, that is, increasing the concentration of thiosulfate, is not conducive to the recovery of precious metals on the anode. The reason is that S2O3 2- As a product, when the voltage is low, S2O3 2- The oxidation degree at the anode is weak, and a large amount of S2O3 does not have time to react. 2- Due to the electric field, the ions are concentrated on the anode surface, thus inhibiting the forward disproportionation reaction; at the same time, high concentrations of S2O3 2- It may also cause the generated precious metal element to dissolve back into the solution. Therefore, the anode precious metal recovery rate at low voltage increases with the S2O3 2- :Cl - The molar ratio increases (thiosulfate concentration increases) and decreases.

[0038] Example 3 (1) Preparation of coated electrode: According to the mass ratio of conductive material to adsorbent material of 1:7, 5 mg of conductive carbon black and 35 mg of activated carbon were weighed in an agate mortar, and 0.4 mL of binder (prepared by dissolving 0.1 g of vinylidene fluoride in 8 mL of NN-dimethylacetamide) was added. All materials were thoroughly ground and mixed. The mixed slurry was evenly coated on a clean titanium plate and dried in a 60°C oven. After cooling, it was soaked in pure water overnight to remove the unadhered materials, and then dried again for use.

[0039] (2) Preparation of precious metal solution: Preparation of S2O3 2- :Cl -A 5 mg / L noble metal solution with a molar ratio of 1:2 is prepared by weighing 2.223 g of ammonium thiosulfate and 2.236 g of potassium chloride, adding them to 148 mL of water for dissolution, and then adding 0.75 mL of chloroauric acid standard solution dropwise. During the process, the pH of the solution is controlled to 10 by adding saturated sodium hydroxide dropwise to obtain 150 mL of noble metal solution.

[0040] (3) Preparation of electrolyte solution: Weigh 3.355 g of potassium chloride and dissolve it in 149 mL of water. Adjust the pH of the solution to 6 with saturated sodium hydroxide to prepare 150 mL of 300 mmol / L electrolyte solution.

[0041] (4) Anode recovery of precious metals: A two-chamber diaphragm electrolytic cell is used as the reaction container, in which the diaphragm is a cation exchange membrane. The two chambers of the electrolytic cell are respectively poured with precious metal solution and electrolyte solution. The side where the precious metal solution is placed is called the anode chamber, and the side where the electrolyte solution is placed is called the cathode chamber. The anode chamber is magnetically stirred at 500 rpm. A pair of coated electrodes are placed in the cathode and cathode chambers of the electrolytic cell, respectively. A DC power supply is used to apply a voltage of 2.5 V (the positive pole of the power supply is connected to the electrode in the precious metal solution), and the precious metal anode recovery test is started. Figure 3 As shown, in high S2O3 2- Concentration, high Cl - Under the conditions of high concentration and high voltage, the anode recovery rate of precious metals was 96.8%, indicating that in high concentration thiosulfate solution, increasing the voltage can significantly improve the recovery rate of precious metals on the anode. Example 4 The same apparatus and method as in Example 3 were used to carry out the precious metal recovery test, except that 0.559 g of potassium chloride was weighed to prepare S2O3 2- :Cl - The molar ratio of the noble metal solution is 1:0.5 (only the chloride ion concentration is reduced compared with Example 3). Figure 3 As shown, the anode recovery rate of the precious metal calculated after the reaction is 95.5%, which is compared with Comparative Example 3, indicating that in a high-concentration thiosulfate solution, even if the chloride ion concentration is appropriately reduced, the recovery rate of the precious metal on the anode can still be significantly improved by increasing the voltage. Compared with Example 3, reducing the chloride ion concentration will slightly reduce the recovery rate of the precious metal on the anode, indicating that in a high-concentration thiosulfate solution, the effect of voltage on the recovery rate of the precious metal is greater than the effect of chloride ion concentration on the recovery rate of the precious metal.

[0042] Comparative Example 3 The precious metal recovery test was carried out using the same apparatus and method as in Example 3, except that the voltage was set to 1.2 V. Figure 3 As shown, in high S2O3 2- Concentration, high Cl -Under the conditions of high concentration and low voltage, the anode recovery rate of precious metals was 0%, indicating that in high concentration thiosulfate solution, despite the increase of chloride ion concentration, the recovery of precious metals could not be achieved under low voltage. The reason may be that a large amount of S2O3 2- Due to the electric field, the ions are enriched on the anode surface, hindering the approach of the noble metal coordination ions and inhibiting the forward progress of the disproportionation reaction; at the same time, the high concentration of S2O3 2- The resulting precious metal may be dissolved back into the solution.

[0043] 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 matters that are not described in detail in some embodiments, reference may be made to the description in other embodiments.

[0044] The above-mentioned embodiments only express the implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for recovering noble metals from thiosulfate solution, characterized in that: The steps include: preparing an electrolyte solution and a thiosulfate solution containing chloride ions respectively; A cation exchange membrane is arranged in the electrolytic cell, wherein the cation exchange membrane separates the electrolytic cell into an anode chamber and a cathode chamber; The thiosulfate solution containing chloride ions is placed in the anode chamber, the electrolyte solution is placed in the cathode chamber, and the electrode system arranged in the electrolytic cell is used to perform electrolysis operation to recover the precious metal deposited on the anode.

2. The method for recovering noble metals from thiosulfate solution according to claim 1, characterized in that: The molar ratio of thiosulfate ions to chloride ions in the chloride-containing thiosulfate solution is (1:0.01)-(1:500).

3. The method for recovering noble metals from thiosulfate solution according to claim 1, characterized in that: The concentration of the noble metal in the chloride ion-containing thiosulfate solution is 0.5-100 mg / L.

4. The method for recovering noble metals from thiosulfate solution according to claim 1, characterized in that: The pH of the thiosulfate solution containing chloride ions is 6-11.

5. The method for recovering precious metals from thiosulfate solution according to claim 1, characterized in that: The voltage of the electrolysis operation is 0.2-4 V.

6. The method for recovering precious metals from thiosulfate solution according to claim 1, characterized in that: The concentration of the electrolyte solution is 0.5-500 mmol / L; the pH of the electrolyte solution is 3-12.

7. The method for recovering noble metals from thiosulfate solution according to claim 1, characterized in that: The precious metal includes gold and / or silver.

8. The method for recovering noble metals from thiosulfate solution according to claim 1, characterized in that: The cathode and the anode of the electrode system are both electrode plates with adsorption material layers on their surfaces.

9. The method for recovering noble metals from thiosulfate solution according to claim 8, characterized in that: The material forming the adsorption material layer includes at least one of activated carbon, graphite, graphene, molybdenum disulfide, and cadmium sulfide.

10. The method for recovering noble metals from thiosulfate solution according to claim 8, characterized in that: The adsorption material layer also includes a conductive material; the electrode plate is one of graphite felt, carbon felt, carbon cloth, carbon paper, titanium plate, and stainless steel plate.

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