Method for recovering gold in thiosulfate solution through electrochemical two-pole synchronous reduction

Abstract

The invention discloses a method for recovering gold in a thiosulfate solution through electrochemical two-pole synchronous reduction, which comprises the following steps of: placing a thiosulfate gold leaching solution in an electrolytic bath, and carrying out electrolysis operation by adopting an electrode system arranged in the electrolytic bath, so that the gold is subjected to reduction deposition at an anode and a cathode; wherein the thiosulfate gold leaching solution contains chloride ions. According to the method, chloride ions are introduced into the thiosulfate gold leaching solution, disproportionation reaction of gold complex ions on the anode is promoted, accordingly, gold in the thiosulfate solution is recovered through electrochemical two-pole synchronous reduction, and the method has the advantages of being high in reduction efficiency, low in energy consumption and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of precious metal recovery, and in particular relates to a method for recovering gold in a thiosulfate solution by electrochemical bipolar synchronous reduction. Background Art

[0002] The development of environmentally friendly cyanide-free gold extraction technology is an inevitable trend to achieve green and clean gold production. Among the cyanide-free gold extraction technologies, the thiosulfate method is considered to have the most potential for industrial application due to its advantages such as fast gold leaching rate, no corrosion to equipment, and strong ore adaptability.

[0003] At present, the technology of recovering gold thiosulfate complex ions (abbreviated as gold complex ions) has developed into chemical precipitation, solvent extraction, electrodeposition, adsorption, etc. The chemical precipitation method obtains a single substance by replacing the gold complex ions with a metal that is more active than gold; this method is easy to operate, but the consumption of metal powder is large. The solvent extraction method realizes the extraction of gold complex ions based on the difference in solubility in different solvents; this method is applicable to a wide range of gold-containing systems, but has high requirements for the concentration and clarity of the solution, and the process flow is relatively complex, the operating cost is high, and it is not suitable for large-scale industrial applications. The electrodeposition method is to reduce the gold complex ions in the solution to a single substance and then recover them by applying a certain voltage or current; this method has become an economical and environmentally friendly method due to its simple operation and high recovery rate, but it is not suitable for low-concentration solutions. The adsorption method adsorbs ions through physical / chemical effects, and commonly used adsorbents include activated carbon, resin, mesoporous silicon, etc.; this method has a simple process and abundant raw materials, but the activated carbon material has a weak affinity for gold complex ions, the resin is expensive, and there are disadvantages such as limited recovery capacity and insufficient selectivity.

[0004] Therefore, it is urgent to develop a new method for recovering gold from thiosulfate 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 a method for recovering gold in a thiosulfate solution by electrochemical bipolar synchronous reduction, so as to solve the problems of high gold complex concentration requirement, low extraction efficiency and high cost when recovering gold from thiosulfate.

[0006] To achieve the above object, the present invention is implemented through the following technical solutions: A method for recovering gold from a thiosulfate solution by electrochemical bipolar synchronous reduction comprises the following steps: The thiosulfate gold leaching solution is placed in an electrolytic cell, and an electrode system arranged in the electrolytic cell is used to perform electrolysis operation, so that gold is reduced and deposited at both the anode and the cathode; wherein the thiosulfate gold leaching solution contains chloride ions. Preferably, the molar ratio of thiosulfate ions to chloride ions in the thiosulfate gold leaching solution is 1:(0.1-500), including but not limited to 1:0.1, 1:0.3, 1:1, 1:10, 1:50, 1:60, 1:90, 1:100, 1:200, 1:300, 1:400, 1:500, etc. Any ratio within the above range. More preferably, it is 1:(10-500), and more preferably, it is 1:(70-410).

[0007] Preferably, the concentration of the thiosulfate gold leaching solution is 0.5-100 mg / L.

[0008] Preferably, the pH of the thiosulfate gold leaching solution is 6-11.

[0009] Preferably, the voltage of the electrolysis operation is 0.1-5 V.

[0010] Preferably, the voltage of the electrolysis operation is 0.6-2.5 V.

[0011] Preferably, the cathode and the anode of the electrode 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 a titanium plate, a stainless steel plate, graphite felt, and carbon paper.

[0015] The beneficial effects of the present invention are: 1. The present invention introduces chloride ions into the thiosulfate gold leaching solution to promote the disproportionation reaction of gold complex ions at the anode, thereby realizing electrochemical bipolar synchronous reduction and recovery of gold in the thiosulfate solution, and the gold recovery rate and recovery rate are greatly improved.

[0016] 2. The present invention provides an adsorption material layer on the electrode plate to generate a chloride ion adsorption layer on the anode, combines the adsorption method with the electrodeposition method, promotes the forward disproportionation reaction, greatly shortens the extraction time, and realizes the efficient extraction of gold. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a comparison diagram of gold recovery effects of Example 1, Comparative Example 1 and Comparative Example 2; Figure 2 The SEM and EDS images of the cathode and anode after synchronous recovery of the two electrodes in Example 1; Figure 3 This is a diagram showing the effect of synchronous recovery of gold at two electrodes under different voltages in Example 2; Figure 4 It is the gold recovery effect diagram of Example 3 and Comparative Example 3; Figure 5 It is the XRD diagram of the cathode and anode after gold recovery in Example 3 and Comparative Example 3. DETAILED DESCRIPTION

[0018] 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.

[0019] Adsorption and electrodeposition methods have been widely studied by scholars because of their simple process, low cost, and good repeatability. Many adsorbents with large specific surface area and multiple active sites have been used to recover gold from aqueous solutions, including activated carbon, functionalized resins, modified cellulose, metal organic framework materials, etc., but these adsorbents still have disadvantages such as poor selectivity, slow kinetics, and low adsorption capacity, which hinder the recovery of gold in actual industrial applications. Electrodeposition is also quite common in the gold recovery process, but its application object is usually a high-concentration solution. When the concentration of gold complex ions is low, adsorption and concentration treatment must be performed first, which increases the process steps, and its operating voltage is relatively high. The operating voltage of industrial electrodeposition of gold is usually above 3.6V. These problems have increased energy consumption and processing costs to a certain extent.

[0020] In view of this, the present invention develops a method for recovering gold from thiosulfate by electrochemical bipolar synchronous reduction to achieve efficient extraction of gold, which specifically includes the following steps: A method for recovering gold from a thiosulfate solution by electrochemical bipolar synchronous reduction comprises the following steps: (1) Grind and mix 20-100 mg of adsorbent material (including but not limited to commercial activated carbon, graphite, graphene, molybdenum disulfide, cadmium sulfide), 1-10 mg of conductive material (such as conductive carbon black) and 0.3-0.6 mL of binder (such as vinylidene fluoride solution) thoroughly, and evenly coat them on a conductive substrate (such as titanium plate, stainless steel plate, graphite felt, carbon paper) to obtain a coated electrode.

[0021] (2) Mixing a thiosulfate gold leaching solution (with a concentration including but not limited to 0.5-100 mg / L) with chloride until the molar ratio of thiosulfate ion to chloride ion in the solution is 1:(0.1-500), and adjusting the pH to 6-11.

[0022] (3) The thiosulfate gold leaching solution of step (2) is placed in an electrolytic cell, and two coated electrodes prepared in step (1) are placed opposite to each other at a spacing of 1-15 mm in the electrolytic cell as the cathode and anode, and a constant voltage (0.1-5.0 V) is supplied by an external DC regulated power supply, so that gold is reduced and deposited at both the anode and the cathode. A convection disturbance device, such as a peristaltic pump, can also be provided in the electrolytic cell to circulate the solution at a speed of 20-100 rpm.

[0023] The present invention combines the effects of cathode reduction and anode electro-adsorption layer by applying a relatively low external voltage to the coating electrode: the cathode provides electrons to the gold complex ions to reduce them (as shown in Formula 1); at the same time, the chloride ions in the solution generate a chloride ion adsorption layer on the anode to induce the disproportionation reaction of the gold complex ions (as shown in Formula 2) and reduce them. Since the chloride ion concentration in the anode adsorption layer is extremely high, and the thiosulfate ions will be oxidized and consumed on the anode, according to the principle of chemical equilibrium shift, the disproportionation reaction will continue to proceed in the positive reaction direction and produce gold element until the gold complex ions in the solution are almost exhausted. Therefore, the present invention realizes the electrochemical bipolar synchronous reduction to recover gold in the thiosulfate solution.

[0024] Cathodic reduction reaction of gold: Au(S2O3)2 3- + e =Au + 2S2O3 2- (1) Anodic reduction reaction of gold: 3Au(S2O3)2 3- + mCl - + nOH - = 2Au + AuCl m (OH) n - + 6S2O3 2- (m+n=4) (2) The present invention is described in detail below with reference to specific embodiments.

[0025] Example 1 (1) Preparation of coated electrode: 40 mg of commercial activated carbon, 5 mg of conductive carbon black and 0.4 mL of binder (prepared by dissolving 0.1 g of vinylidene fluoride in 8 mL of NN-dimethylacetamide) were fully ground and mixed to obtain a slurry. The slurry was then evenly coated on a titanium plate substrate and dried in a forced air oven. After being taken out and cooled to room temperature, it was soaked in pure water for 8 h to remove the unadhered adsorbent material. Finally, it was dried again for use.

[0026] (2) Preparation of gold complex ion solution: According to S2O3 2- :Cl -Prepare 200 mL of 25 mg / L gold complex ion solution at a molar ratio of 1:74, namely, weigh 15 mg of ammonium thiosulfate and add 194 mL of water to dissolve it, and then add 5 mL of chloroauric acid standard solution (containing 7.5 mmol Cl - ), during which the solution pH was controlled to 10 by adding saturated sodium hydroxide.

[0027] (3) Bipolar reduction and recovery of gold: Add 200 mL of the above 25 mg / L gold complex ion solution to a homemade electrolytic cell, wherein the two ends of the electrolytic cell are connected to a peristaltic pump through a hose to circulate the solution at a speed of 50 rpm. Two coated electrodes are placed opposite to each other in the electrolytic cell at a spacing of 3 mm as the cathode and anode, and a constant voltage of 1.2 V is supplied by an external DC regulated power supply to conduct a bipolar reduction and recovery test of gold. After the reaction is completed, samples are taken and filtered, and the residual gold concentration of the solution is tested and the gold recovery rate and reaction rate are calculated. The two electrodes after the reaction are rinsed with pure water several times and dried, and then the composition of the electrode material is characterized.

[0028] like Figure 1 As shown, the gold recovery rate of this embodiment is 98.1%, and the reaction rate is 0.1571 h -1 The electrode material after reaction was characterized by SEM. Figure 2 As shown, it was found that obvious nano-gold particles were generated on both the cathode material and the anode material, indicating that the method of the present invention achieves electrochemical bipolar synchronous reduction and recovery of gold.

[0029] Comparative Example 1 The same device as in Example 1 was used to carry out the experiment of recovering gold by conventional electrodeposition, that is, the difference from Example 1 was that both the positive and negative electrodes were pure titanium plates without an adsorption material layer. Figure 1 As shown in the figure, after the reaction, the gold recovery rate was calculated to be 29.0% and the reaction rate was 0.0632 h -1 The gold recovery performance is lower than that of Example 1, indicating that the traditional electrodeposition method has poor reduction and recovery performance for gold complex ions.

[0030] Comparative Example 2 The same apparatus as in Example 1 was used to carry out the gold recovery experiment using activated carbon, that is, the difference from Example 1 was that the coated electrode was replaced with 40 mg of commercial activated carbon, the solution circulation method was replaced with magnetic stirring at a speed of 300 rpm, and no voltage was applied. Figure 1 As shown in the figure, after the reaction, the gold recovery rate was calculated to be 29.8% and the reaction rate was 0.0166 h -1 The gold recovery effect is lower than that in Example 1, indicating that the adsorption capacity of the pure activated carbon material for gold complex ions is very limited.

[0031] Example 2 (1) Preparation of coated electrode: 35 mg of molybdenum disulfide, 4 mg of conductive carbon black and 0.3 mL of binder (prepared by dissolving 0.1 g of vinylidene fluoride in 8 mL of NN-dimethylacetamide) were fully ground and mixed, and evenly coated on the titanium plate substrate. The substrate was placed in a forced air oven for drying, taken out and cooled to room temperature, and then soaked in pure water for 8 h to remove the unadhered adsorbent material. The substrate was dried again for later use.

[0032] (2) Preparation of gold complex ion solution: According to S2O3 2- :Cl - Prepare 200 mL of 3 mg / L gold complex ion solution at a molar ratio of 1:74 by weighing 1.8 mg of ammonium thiosulfate and adding it to 199 mL of water for dissolution, and then add 0.6 mL of chloroauric acid standard solution (containing 0.9 mmol Cl - ), during the process, the solution pH was controlled to 10 by adding saturated sodium hydroxide. Five groups of solutions were prepared according to the same steps.

[0033] (3) Bipolar reduction recovery of gold: Five groups of solutions were added to five homemade electrolytic cells, where the two ends of the electrolytic cells were connected to peristaltic pumps through hoses to circulate the solutions at a speed of 45 rpm. Two coated electrodes were placed opposite each other at a spacing of 1 mm in the electrolytic cell as the cathode and anode. Constant voltages of 0.4 V, 0.8 V, 1.2 V, 2.5 V, and 4.0 V were supplied by an external DC regulated power supply, and the bipolar reduction recovery test of gold was started. After the reaction was completed, samples were taken and filtered, and the residual gold concentration of the solution was tested, and the gold recovery rate and reaction rate were calculated.

[0034] like Figure 3 As shown, the gold recoveries were 10.0%, 95.6%, 98.0%, 91.2%, and 92.4%, respectively, and the reaction rates were 0.01871 h -1 , 0.05258 h -1 , 0.69078 h -1 , 0.50595 h -1 , 0.46408 h -1 It can be seen that increasing the voltage is beneficial to the synchronous recovery of gold at the two electrochemical electrodes, but when the voltage is too high, the recovery rate will decrease. The reason may be that side reactions such as hydrogen evolution will occur under excessively high voltage, which reduces the current efficiency of gold reduction.

[0035] Example 3 (1) Preparation of coated electrode: 40 mg of commercial activated carbon, 5 mg of conductive carbon black and 0.4 mL (prepared by dissolving 0.1 g of vinylidene fluoride in 8 mL of NN-dimethylacetamide) were fully ground and mixed to obtain a slurry. The slurry was then evenly coated on a titanium plate substrate and dried in a forced air oven. After being taken out and cooled to room temperature, it was soaked in pure water for 8 h to remove the unadhered adsorbent material, and finally dried again for use.

[0036] (2) Preparation of gold complex ion solution: According to S2O3 2- :Cl - Prepare 200 mL of 15 mg / L gold complex ion solution at a molar ratio of 1:403 by weighing 9 mg of ammonium thiosulfate and 1.17 g of sodium chloride (containing 20 mmol Cl - ) was dissolved in 196 mL of water, and 3 mL of chloroauric acid standard solution (containing 4.5 mmol Cl) was added dropwise. - ), during which the solution pH was controlled to 10 by adding saturated sodium hydroxide.

[0037] (3) Bipolar reduction recovery of gold: Add 200 mL of the above 15 mg / L gold complex ion solution into a homemade electrolytic cell, wherein the two ends of the electrolytic cell are connected to a peristaltic pump through a hose to circulate the solution at a speed of 55 rpm. Two coated electrodes are placed opposite to each other at a spacing of 4 mm in the electrolytic cell as the cathode and anode. A constant voltage of 0.8 V is supplied by an external DC regulated power supply to start the bipolar reduction recovery test of gold. After the reaction is completed, samples are taken and filtered, the residual gold concentration of the solution is tested, and the gold recovery rate and reaction rate are calculated.

[0038] like Figure 4 As shown in the figure, after the reaction, the gold recovery rate was 99.3% and the reaction rate was 0.16169 h -1 The two electrodes after the reaction were rinsed with pure water several times and dried, and then the electrode materials were characterized by XRD, such as Figure 5 As shown, the results showed that gold was generated on both the anode and cathode materials, indicating that when the concentration of chloride ions as reactants increased, it would promote the forward disproportionation reaction and promote the electrochemical recovery of gold at both electrodes.

[0039] Comparative Example 3 The same apparatus as in Example 3 was used to carry out high S2O3 2- :Cl - The experiment of recovering gold by molar ratio is different from that of Example 3 in that 2.973 g of ammonium thiosulfate is weighed, no sodium chloride is added, and a standard solution of chloroauric acid is added to prepare S2O3 2- :Cl - A gold complex ion solution with a molar ratio of 1:0.225 was prepared, and a gold recovery test was performed. After the reaction was completed, a sample was taken and filtered, and the residual gold concentration of the solution was tested and the gold recovery rate and reaction rate were calculated.

[0040] like Figure 4 As shown in the figure, after the reaction, the gold recovery rate was 84.9% and the reaction rate was 0.05404 h -1 The two electrodes after the reaction were rinsed with pure water several times and dried, and then the electrode materials were characterized by XRD, such as Figure 5 As shown, the results showed that only gold was generated on the cathode material, indicating that when the concentration of thiosulfate ions as the product increased, the disproportionation reaction would be reversed, reducing the reduction of gold at the anode, thereby inhibiting the electrochemical bipolar recovery of gold.

[0041] 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.

[0042] 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 gold from a thiosulfate solution by electrochemical bipolar synchronous reduction, characterized in that: The steps include: Placing the thiosulfate gold leaching solution in an electrolytic cell, and performing electrolysis using an electrode system disposed in the electrolytic cell, so that gold is reduced and deposited at both the anode and the cathode; Wherein, the thiosulfate gold leaching solution contains chloride ions.

2. The method for recovering gold from thiosulfate solution by electrochemical bipolar synchronous reduction according to claim 1, characterized in that: The molar ratio of thiosulfate ions to chloride ions in the thiosulfate gold leaching solution is 1:(0.1-500).

3. The method for recovering gold in thiosulfate solution by electrochemical bipolar synchronous reduction according to claim 1, characterized in that: The concentration of the thiosulfate gold leaching solution is 0.5-100 mg / L.

4. The method for recovering gold in thiosulfate solution by electrochemical bipolar synchronous reduction according to claim 1, characterized in that: The pH of the thiosulfate gold leaching solution is 6-11.

5. The method for recovering gold in thiosulfate solution by electrochemical bipolar synchronous reduction according to claim 1, characterized in that: The voltage of the electrolysis operation is 0.1-5 V.

6. The method for recovering gold from thiosulfate solution by electrochemical bipolar synchronous reduction according to claim 5, characterized in that: The voltage of the electrolysis operation is 0.6-2.5 V.

7. The method for recovering gold from thiosulfate solution by electrochemical bipolar synchronous reduction 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.

8. The method for recovering gold from thiosulfate solution by electrochemical bipolar synchronous reduction according to claim 7, characterized in that: The material forming the adsorption material layer includes at least one of activated carbon, graphite, graphene, molybdenum disulfide, and cadmium sulfide.

9. The method for recovering gold from thiosulfate solution by electrochemical bipolar synchronous reduction according to claim 7, characterized in that: The adsorption material layer also includes conductive material.

10. The method for recovering gold from thiosulfate solution by electrochemical bipolar synchronous reduction according to claim 7, characterized in that: The electrode plate is one of a titanium plate, a stainless steel plate, a graphite felt and a carbon paper.

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