Method for preparing high-purity gold ingot from silver anode slime and high-purity gold ingot

Abstract

The present application relates to the technical field of rare and precious metal refining, and particularly relates to a method for preparing high-purity gold ingot from silver anode slime and high-purity gold ingot, comprising the following steps: crushing and grinding the silver anode slime, mixing the silver anode slime with a chlorine-free composite leaching agent, and filtering to obtain gold-containing leaching residue and impurity-containing leaching solution; washing and drying the gold-containing leaching residue to obtain gold-enriched residue; mixing the gold-enriched residue with a decontamination agent, and filtering to obtain pure gold residue and decontamination waste liquid; mixing the pure gold residue with a reducing liquid, adjusting the pH value to 1.0-2.0, and filtering to obtain sponge gold; washing the sponge gold to neutral, melting and casting ingot at 1100-1200 DEG C, naturally cooling after heat preservation for 20-30 min, and obtaining high-purity gold ingot. The present application realizes efficient separation of most impurities such as silver and copper by using a nitric acid-sulfuric acid composite leaching agent, and then removes residual trace impurities such as palladium and silver by using a hydrochloric acid-sulfuric acid decontamination agent, and finally, the purity of the high-purity gold ingot is greater than or equal to 99.99% by using an oxalic acid-hydrochloric acid reducing system to accurately control the reduction process.

Description

Technical Field

[0001] This invention relates to the field of rare and precious metal refining technology, specifically to a method for preparing high-purity gold ingots from silver anode mud and the high-purity gold ingots themselves. Background Technology

[0002] Gold, as a scarce precious metal, holds an irreplaceable position in fields such as electronics, aerospace, financial reserves, and jewelry due to its excellent physicochemical properties. The purity of its products directly determines their application value and economic benefits. Silver anode mud, generated during silver electrolytic refining, is an important secondary resource for gold recovery. Although the gold content is considerable, it contains a large amount of valuable or harmful impurities such as silver, palladium, copper, selenium, and tellurium. How to efficiently, environmentally, and cost-effectively separate these impurities from this complex system to prepare high-purity gold ingots of over 99.99% purity is a core technical challenge in the field of rare and precious metal refining.

[0003] Currently, the mainstream processes for gold extraction from silver anode mud are wet chlorination systems or combined wet-fire processes, typically such as the "hydrochloric acid pre-leaching-sodium chlorate gold separation" process. This process uses chlorine-containing reagents to dissolve gold into chloroauric acid, while silver ions form insoluble silver chloride precipitate (i.e., gold separation slag). This slag is physically viscous, difficult to wash, and easily traps gold particles, leading to gold resource occupation or loss. To recover this gold, the slag needs to be returned to pyrometallurgical smelting, which not only prolongs the process, increases energy consumption and production cycle, but also causes further gold loss due to high-temperature volatilization and smelting slag. Furthermore, chlorine-containing reagents are highly corrosive, and the disposal cost of the gold separation slag as hazardous waste is high, placing a heavy environmental burden on enterprises.

[0004] To overcome the aforementioned shortcomings, chlorine-free wet gold extraction processes have become a research hotspot, with the core objective being to prevent the generation of gold separation slag at its source. Chinese patent CN106119554A discloses a method for extracting gold from silver anode mud. Its first step uses nitric acid to separate silver, avoiding the formation of silver chloride precipitate. However, the subsequent treatment of the silver separation slag still relies on aqua regia (a chlorine-containing reagent) to dissolve the gold, and the process requires returning the gold to the Kaldor furnace for pyrometallurgical smelting. It has not completely eliminated the dependence on chlorine-containing reagents and pyrometallurgical treatment, and still suffers from problems such as gold loss and significant environmental pressure.

[0005] Other related improvements also have shortcomings: although some technologies have achieved preliminary enrichment of gold through chlorine-free oxidizing acids such as nitric acid, they only remain at the level of principle disclosure and do not provide a complete industrial-scale deep purification solution for the complex silver anode mud system. In particular, they lack efficient means to remove residual trace impurities such as palladium and silver from the gold slag after leaching, making it difficult to stably produce high-purity gold of 99.99% or higher. Other processes use solvent extraction, roasting and other steps, which have problems such as complex processes, high reagent costs, easy secondary pollution or high energy consumption, which limit large-scale industrial applications. Summary of the Invention

[0006] To address the problems existing in the prior art, the present invention provides a method for preparing high-purity gold ingots from silver anode mud and the high-purity gold ingots themselves.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] A method for preparing high-purity gold ingots from silver anode mud includes the following steps:

[0009] (1) Chlorine-free selective leaching: Silver anode mud is crushed and ground to a particle size ≤120 mesh, mixed with chlorine-free composite leaching agent at a liquid-solid ratio of 10-14:1, reacted at 65-75℃ for 3-4 hours, and filtered to obtain gold-containing leaching residue and impurity-containing leaching solution; the chlorine-free composite leaching agent includes nitric acid and sulfuric acid, and the volume ratio of nitric acid and sulfuric acid is 2-3:1;

[0010] (2) Washing of leaching residue: The gold-containing leaching residue obtained in step (1) is washed and dried to obtain gold-enriched residue;

[0011] (3) Selective impurity removal: The enriched gold slag and the impurity removal agent are mixed at a liquid-solid ratio of 12-16:1 and reacted at 50-60℃ for 2-3 hours. The mixture is then filtered to obtain pure gold slag and impurity removal waste liquid. The impurity removal agent is a mixed solution of hydrochloric acid and sodium sulfite, with a hydrochloric acid concentration of 1.5-2.0 mol / L and a sodium sulfite concentration of 0.8-1.2 mol / L.

[0012] (4) Reduction and purification: The pure gold slag and the reducing solution are mixed at a liquid-solid ratio of 15-18:1, the pH value is adjusted to 1.0-2.0, and the reaction is carried out at 70-80℃ for 2.5-3.5h. The gold sponge is obtained by filtration. The reducing solution is a mixed solution of oxalic acid and hydrochloric acid, with an oxalic acid concentration of 0.5-0.8mol / L and a hydrochloric acid concentration of 0.3-0.5mol / L.

[0013] (5) Ingot casting: The sponge gold is washed until neutral, melted and cast at 1100-1200℃, kept at the temperature for 20-30 minutes and then cooled naturally to obtain a high-purity gold ingot.

[0014] Further, in step (1), the composition of the silver anode mud by mass percentage is: Au 15.0-35.0%, Ag 45.0-65.0%, Pd 0.8-1.5%, Cu 0.2-0.4%, and the remainder is impurities.

[0015] Further, in step (2), the gold-containing leaching residue is washed with deionized water 3-4 times, with a liquid-to-solid ratio of 8-10:1 each time and a washing time of 15-20 minutes.

[0016] Furthermore, in step (3), palladium is recovered by adsorption of the impurity-removing waste liquid using chelating resin.

[0017] Furthermore, in step (4), the purity of the sponge gold is ≥99.995%.

[0018] This invention also includes the following technical solutions:

[0019] A high-purity gold ingot prepared using the above method.

[0020] Furthermore, the purity of the high-purity gold ingot is ≥99.99%, wherein the silver content is ≤0.003%, the palladium content is ≤0.002%, the copper content is ≤0.001%, and the total content of other impurities is ≤0.004%.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention provides a method for preparing high-purity gold ingots from silver anode mud, and the high-purity gold ingots themselves. The method employs a fully wet process involving chlorine-free selective leaching, leaching residue washing, selective impurity removal, reduction purification, and ingot casting. This process completely eliminates chlorine-containing reagents, preventing the generation of gold-separating slag at the source and eliminating the need for pyrometallurgical remelting. It completely solves the problems of gold entrainment loss, lengthy processes, high energy consumption, equipment corrosion, and high hazardous waste disposal pressure associated with traditional chlorination systems. The method utilizes a nitric acid-sulfuric acid composite leaching agent to achieve efficient separation of most impurities such as silver and copper, and further combines this with a hydrochloric acid-sodium sulfite impurity removal agent to specifically remove residual trace amounts of palladium, silver, and other impurities. By precisely controlling the reduction process using an oxalic acid-hydrochloric acid reduction system, and through multi-step synergy, the process ensures a high degree of impurity removal and a high gold recovery rate. Ultimately, it can stably produce high-purity gold ingots with a purity ≥99.99%, where the contents of silver, palladium, and copper are controlled below 0.003%, 0.002%, and 0.001%, respectively. The process is simple, controllable, and highly integrated, with reasonable reagent consumption. The waste liquid from impurity removal can be recycled to recover palladium through chelating resin, achieving resource reuse. It has significant economic and environmental benefits, is suitable for large-scale industrial production, and provides a green and feasible solution for the efficient extraction of gold from low-grade silver anode mud. Attached Figure Description

[0023] The embodiments of the present invention will be further described below with reference to the accompanying drawings, wherein:

[0024] Figure 1 A process flow diagram of the present invention is shown. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] Reference Appendix Figure 1 A method for preparing high-purity gold ingots from silver anode mud includes the following steps:

[0027] (1) Chlorine-free selective leaching: Silver anode mud is crushed and ground to a particle size ≤120 mesh, mixed with chlorine-free composite leaching agent at a liquid-solid ratio of 10-14:1, reacted at 65-75℃ for 3-4 hours, and filtered to obtain gold-containing leaching residue and impurity-containing leaching solution; the chlorine-free composite leaching agent includes nitric acid and sulfuric acid, and the volume ratio of nitric acid and sulfuric acid is 2-3:1;

[0028] (2) Washing of leaching residue: The gold-containing leaching residue obtained in step (1) is washed and dried to obtain gold-enriched residue;

[0029] (3) Selective impurity removal: The enriched gold slag and the impurity removal agent are mixed at a liquid-solid ratio of 12-16:1 and reacted at 50-60℃ for 2-3 hours. The mixture is then filtered to obtain pure gold slag and impurity removal waste liquid. The impurity removal agent is a mixed solution of hydrochloric acid and sodium sulfite, with a hydrochloric acid concentration of 1.5-2.0 mol / L and a sodium sulfite concentration of 0.8-1.2 mol / L.

[0030] (4) Reduction and purification: The pure gold slag and the reducing solution are mixed at a liquid-solid ratio of 15-18:1, the pH value is adjusted to 1.0-2.0, and the reaction is carried out at 70-80℃ for 2.5-3.5h. The gold sponge is obtained by filtration. The reducing solution is a mixed solution of oxalic acid and hydrochloric acid, with an oxalic acid concentration of 0.5-0.8mol / L and a hydrochloric acid concentration of 0.3-0.5mol / L.

[0031] (5) Ingot casting: The sponge gold is washed until neutral, melted and cast at 1100-1200℃, kept at the temperature for 20-30 minutes and then cooled naturally to obtain a high-purity gold ingot.

[0032] In one embodiment of the present invention, in step (1), the composition of the silver anode mud by mass percentage is: Au 15.0-35.0%, Ag 45.0-65.0%, Pd 0.8-1.5%, Cu 0.2-0.4%, and the remainder is impurities.

[0033] In one embodiment of the present invention, in step (2), the gold-containing leaching residue is washed with deionized water 3-4 times, with a liquid-to-solid ratio of 8-10:1 each time and a washing time of 15-20 minutes.

[0034] In one embodiment of the present invention, in step (3), palladium is recovered by adsorption of the impurity removal waste liquid using chelating resin.

[0035] In one embodiment of the present invention, in step (4), the purity of the sponge gold is ≥99.995%.

[0036] Example 1

[0037] A method for preparing high-purity gold ingots from silver anode mud includes the following steps:

[0038] (1) Chlorine-free selective leaching: Silver anode mud (composition: Au 15.0%, Ag 65.0%, Pd 1.5%, Cu 0.4%, the remainder being impurities) was crushed and ground to a particle size ≤120 mesh. It was then mixed with a chlorine-free composite leaching agent (nitric acid to sulfuric acid volume ratio 2:1) at a liquid-to-solid ratio of 10:1 and placed in a reaction apparatus. The mixture was kept at a constant temperature of 65℃ for 3 hours, with continuous stirring during the reaction. After the reaction was completed, the mixture was filtered to obtain gold-containing leaching residue and impurity-containing leaching solution.

[0039] (2) Washing of leaching residue: The gold-containing leaching residue was washed three times with deionized water, with a liquid-to-solid ratio of 8:1 each time and a washing time of 15 minutes. After drying, the gold-enriched residue was obtained.

[0040] (3) Selective impurity removal: The enriched gold slag and the impurity removal agent (hydrochloric acid concentration 1.5 mol / L, sodium sulfite concentration 0.8 mol / L) were mixed at a liquid-solid ratio of 12:1, and the temperature was controlled at 50℃ for 2 hours. Pure gold slag and impurity removal waste liquid were obtained by filtration. Palladium was recovered from the impurity removal waste liquid by adsorption with chelating resin.

[0041] (4) Reduction and purification: Pure gold slag and reducing solution (oxalic acid concentration 0.5mol / L, hydrochloric acid concentration 0.3mol / L) are mixed at a liquid-solid ratio of 15:1, the pH value is adjusted to 1.0, and the reaction is carried out at 70℃ for 2.5h. The sponge gold is obtained by filtration.

[0042] (5) Casting: The sponge gold is washed with deionized water until neutral, melted and cast at 1100℃, kept at the temperature for 20 minutes and then cooled naturally to obtain a high-purity gold ingot.

[0043] Tests showed that the high-purity gold ingot had a purity of 99.991%, with a silver content of 0.0028%, a palladium content of 0.0017%, a copper content of 0.0009%, and a total content of other impurities of 0.0036%.

[0044] Example 2

[0045] A method for preparing high-purity gold ingots from silver anode mud includes the following steps:

[0046] (1) Chlorine-free selective leaching: Silver anode mud (composition: Au 35.0%, Ag 45.0%, Pd 0.8%, Cu 0.2%, the remainder being impurities) was crushed and ground to a particle size ≤120 mesh. It was then mixed with a chlorine-free composite leaching agent (nitric acid to sulfuric acid volume ratio 3:1) at a liquid-to-solid ratio of 14:1 and placed in a reaction apparatus. The mixture was kept at a constant temperature of 75°C for 4 hours, with continuous stirring during the reaction. After filtration, gold-containing leaching residue and impurity-containing leaching solution were obtained.

[0047] (2) Washing of leaching residue: The gold-containing leaching residue was washed 4 times with deionized water, with a liquid-to-solid ratio of 10:1 each time and a washing time of 20 minutes. After drying, the gold-enriched residue was obtained.

[0048] (3) Selective impurity removal: The enriched gold slag and the impurity removal agent (hydrochloric acid concentration 2.0 mol / L, sodium sulfite concentration 1.2 mol / L) were mixed at a liquid-solid ratio of 16:1, and the temperature was controlled at 60℃ for 3 hours. Pure gold slag and impurity removal waste liquid were obtained by filtration. Palladium was recovered from the impurity removal waste liquid by adsorption with chelating resin.

[0049] (4) Reduction and purification: Pure gold slag and reducing solution (oxalic acid concentration 0.8mol / L, hydrochloric acid concentration 0.5mol / L) are mixed at a liquid-solid ratio of 18:1, the pH value is adjusted to 2.0, and the reaction is carried out at 80℃ for 3.5h. The sponge gold is obtained by filtration.

[0050] (5) Casting: The sponge gold is washed until neutral, melted and cast at 1200℃, kept at the temperature for 30 minutes and then cooled naturally to obtain a high-purity gold ingot.

[0051] Tests showed that the high-purity gold ingot had a purity of 99.993%, with a silver content of 0.0025%, a palladium content of 0.0015%, a copper content of 0.0008%, and a total content of other impurities of 0.0032%.

[0052] Example 3

[0053] A method for preparing high-purity gold ingots from silver anode mud includes the following steps:

[0054] (1) Chlorine-free selective leaching: Silver anode mud (composition: Au 25.0%, Ag 55.0%, Pd 1.2%, Cu 0.3%, the remainder being impurities) was crushed and ground to a particle size ≤120 mesh. It was then mixed with a chlorine-free composite leaching agent (nitric acid to sulfuric acid volume ratio 2.5:1) at a liquid-to-solid ratio of 12:1 and placed in a reaction apparatus. The mixture was kept at a constant temperature of 70℃ for 3.5 h, with continuous stirring during the reaction. The residue containing gold and the leachate containing impurities were obtained by filtration.

[0055] (2) Washing of leaching residue: The gold-containing leaching residue was washed three times with deionized water, with a liquid-to-solid ratio of 9:1 each time and a washing time of 18 minutes. After drying, the gold-enriched residue was obtained.

[0056] (3) Selective impurity removal: The enriched gold slag was mixed with the impurity removal agent (hydrochloric acid concentration 1.8 mol / L, sodium sulfite concentration 1.0 mol / L) at a liquid-to-solid ratio of 14:1, and the reaction was carried out at 55℃ for 2.5 h. The pure gold slag and the impurity removal waste liquid were obtained by filtration. The palladium was recovered by adsorption of the impurity removal waste liquid using chelating resin.

[0057] (4) Reduction and purification: Pure gold slag and reducing solution (oxalic acid concentration 0.65mol / L, hydrochloric acid concentration 0.4mol / L) are mixed at a liquid-solid ratio of 16:1, the pH value is adjusted to 1.5, and the reaction is carried out at 75℃ for 3.0h. The sponge gold is obtained by filtration.

[0058] (5) Casting: The sponge gold is washed until neutral, melted and cast at 1150℃, kept at the temperature for 25 minutes and then cooled naturally to obtain a high-purity gold ingot.

[0059] The test results showed that the high-purity gold ingot had a purity of 99.992%, with a silver content of 0.0026%, a palladium content of 0.0016%, a copper content of 0.0008%, and a total content of other impurities of 0.0034%.

[0060] This invention provides a method for preparing high-purity gold ingots from silver anode mud, and the high-purity gold ingots themselves. The method employs a fully wet process involving chlorine-free selective leaching, leaching residue washing, selective impurity removal, reduction purification, and ingot casting. This process completely eliminates chlorine-containing reagents, preventing the generation of gold-separating slag at the source and eliminating the need for pyrometallurgical remelting. It completely solves the problems of gold entrainment loss, lengthy processes, high energy consumption, equipment corrosion, and high hazardous waste disposal pressure associated with traditional chlorination systems. The method utilizes a nitric acid-sulfuric acid composite leaching agent to achieve efficient separation of most impurities such as silver and copper, and further combines this with a hydrochloric acid-sodium sulfite impurity removal agent to specifically remove residual trace amounts of palladium, silver, and other impurities. By precisely controlling the reduction process using an oxalic acid-hydrochloric acid reduction system, and through multi-step synergy, the process ensures a high degree of impurity removal and a high gold recovery rate. Ultimately, it can stably produce high-purity gold ingots with a purity ≥99.99%, where the contents of silver, palladium, and copper are controlled below 0.003%, 0.002%, and 0.001%, respectively. The process is simple, controllable, and highly integrated, with reasonable reagent consumption. The waste liquid from impurity removal can be recycled to recover palladium through chelating resin, achieving resource reuse. It has significant economic and environmental benefits, is suitable for large-scale industrial production, and provides a green and feasible solution for the efficient extraction of gold from low-grade silver anode mud.

[0061] This invention provides a method for preparing high-purity gold ingots from silver anode mud, and the high-purity gold ingots themselves. The method employs a fully wet process involving chlorine-free selective leaching, leaching residue washing, selective impurity removal, reduction purification, and ingot casting. This process completely eliminates chlorine-containing reagents, preventing the generation of gold-separating slag at the source and eliminating the need for pyrometallurgical remelting. It completely solves the problems of gold entrainment loss, lengthy processes, high energy consumption, equipment corrosion, and high hazardous waste disposal pressure associated with traditional chlorination systems. The method utilizes a nitric acid-sulfuric acid composite leaching agent to achieve efficient separation of most impurities such as silver and copper, and further combines this with a hydrochloric acid-sodium sulfite impurity removal agent to specifically remove residual trace amounts of palladium, silver, and other impurities. By precisely controlling the reduction process using an oxalic acid-hydrochloric acid reduction system, and through multi-step synergy, the process ensures a high degree of impurity removal and a high gold recovery rate. Ultimately, it can stably produce high-purity gold ingots with a purity ≥99.99%, where the contents of silver, palladium, and copper are controlled below 0.003%, 0.002%, and 0.001%, respectively. The process is simple, controllable, and highly integrated, with reasonable reagent consumption. The waste liquid from impurity removal can be recycled to recover palladium through chelating resin, achieving resource reuse. It has significant economic and environmental benefits, is suitable for large-scale industrial production, and provides a green and feasible solution for the efficient extraction of gold from low-grade silver anode mud.

[0062] The foregoing descriptions have outlined some exemplary embodiments of the present invention. It is understood that these embodiments are merely illustrative and do not constitute a limitation on the scope of protection of the present invention. Features in these embodiments can be rearranged in suitable ways, and the resulting solutions remain within the scope of protection claimed by the present invention. All other embodiments obtained by those skilled in the art based on the foregoing embodiments without inventive effort, i.e., all modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing high-purity gold ingots from silver anode mud, characterized in that, Includes the following steps: (1) Chlorine-free selective leaching: Silver anode mud is crushed and ground to a particle size ≤120 mesh, mixed with chlorine-free composite leaching agent at a liquid-solid ratio of 10-14:1, reacted at 65-75℃ for 3-4 hours, and filtered to obtain gold-containing leaching residue and impurity-containing leaching solution; the chlorine-free composite leaching agent includes nitric acid and sulfuric acid, and the volume ratio of nitric acid and sulfuric acid is 2-3:1; (2) Washing of leaching residue: The gold-containing leaching residue obtained in step (1) is washed and dried to obtain gold-enriched residue; (3) Selective impurity removal: The enriched gold slag and the impurity removal agent are mixed at a liquid-solid ratio of 12-16:1 and reacted at 50-60℃ for 2-3 hours. The mixture is then filtered to obtain pure gold slag and impurity removal waste liquid. The impurity removal agent is a mixed solution of hydrochloric acid and sodium sulfite, with a hydrochloric acid concentration of 1.5-2.0 mol / L and a sodium sulfite concentration of 0.8-1.2 mol / L. (4) Reduction and purification: The pure gold slag and the reducing solution are mixed at a liquid-solid ratio of 15-18:1, the pH value is adjusted to 1.0-2.0, and the reaction is carried out at 70-80℃ for 2.5-3.5h. The gold sponge is obtained by filtration. The reducing solution is a mixed solution of oxalic acid and hydrochloric acid, with an oxalic acid concentration of 0.5-0.8mol / L and a hydrochloric acid concentration of 0.3-0.5mol / L. (5) Ingot casting: The sponge gold is washed until neutral, melted and cast at 1100-1200℃, kept at the temperature for 20-30 minutes and then cooled naturally to obtain a high-purity gold ingot.

2. The method for preparing high-purity gold ingots from silver anode mud according to claim 1, characterized in that, In step (1), the composition of the silver anode mud by mass percentage is: Au 15.0-35.0%, Ag 45.0-65.0%, Pd 0.8-1.5%, Cu 0.2-0.4%, and the remainder is impurities.

3. The method for preparing high-purity gold ingots from silver anode mud according to claim 1, characterized in that, In step (2), the gold-containing leaching residue is washed with deionized water 3-4 times, with a liquid-to-solid ratio of 8-10:1 each time and a washing time of 15-20 minutes.

4. The method for preparing high-purity gold ingots from silver anode mud according to claim 1, characterized in that, In step (3), palladium is recovered by chelating resin adsorption of the waste liquid after impurity removal.

5. The method for preparing high-purity gold ingots from silver anode mud according to claim 1, characterized in that, In step (4), the purity of the sponge gold is ≥99.995%.

6. A high-purity gold ingot prepared by any one of the methods described in claims 1-5.

7. A high-purity gold ingot according to claim 6, characterized in that, The high-purity gold ingot has a purity of ≥99.99%, wherein the silver content is ≤0.003%, the palladium content is ≤0.002%, the copper content is ≤0.001%, and the total content of other impurities is ≤0.004%.

Images