How to leach gold from copper anode mud

Extraction of gold and silver from copper anode mud

Extraction of gold and silver from copper anode mud

The process of enriching and recovering gold and silver from copper electrolytic anode mud is an important link to extract gold from metallurgical by-products. Copper anode mud is composed of many substances insoluble in electrolyte during electrolytic refining of copper anode, and its phase composition is complex. Among them, silver is mainly Ag, Ag2Se, Ag2Te, CuAgSe and AgCl, and gold is in (Ag, Au)Te2 or free state. The composition of copper anode mud varies from place to place. The general components (ω/%) are: Cu 10 ~ 25, Au 0.5 ~ 5, Ag 5 ~ 30, Se 2 ~ 28, Te 0. 1 ~ 8, Pb1~ 25; In addition, it also contains a small amount of bismuth, antimony, arsenic, iron, Al2O3, SiO2, and a small amount of palladium and platinum, with a moisture content of 20% ~ 40%. Most large smelters treat copper anode slime by pyrolysis-electrolysis method, and develop leaching copper removal and wet treatment processes. Pyrolysis-electrolysis method is commonly known as traditional method.

The traditional process flow is basically the same as that of copper anode mud treatment. The main process flow is: (1) sulfate roasting distillation to remove selenium, leaching roasting slag to remove copper; (2) the leaching residue is reduced and smelted to produce expensive lead alloy; (3) oxidizing and refining the lead-precious metal alloy into a gold-silver alloy, namely an anode plate; (4) silver electrolysis; (5) pretreating the silver anode mud, and then carrying out gold electrolysis. The traditional process is long and complicated, and the direct yield of metal is not high. Therefore, a new process for treating copper anode slime has emerged. Although these new processes have replaced the traditional processes to some extent, they are still the improvement of the traditional processes in essence.

The improvement methods of traditional technology include low-temperature sulfation roasting-wet treatment, low-temperature oxidation roasting-wet treatment, sulfation roasting-wet precipitation of gold and silver, flotation enrichment of gold and silver, Sumitomo method and wet treatment. They can better protect the environment, shorten the production cycle, speed up the capital turnover and improve the economic benefits of enterprises. Anode mud contains high copper content, which is beneficial to the early extraction of gold and silver. Therefore, the new technology has improved the copper removal method to varying degrees.

The technological process of low-temperature sulfation roasting-wet treatment is shown in figure 1. The main processes are as follows: (1) low-temperature sulfation roasting distillation of copper anode mud to remove selenium (573 ~ 953 k); (2) leaching the selenium removal residue after distillation with H2SO4+NaCl solution to remove copper; (3) leaching silver from the copper removal residue with ammonia water; (4) reducing the silver in the silver ammonia solution with hydrazine hydrate, and sending the obtained silver powder to silver electrolysis; (5) Na2CO3 is added into the stripping slag to convert chloride and sulfate of lead into lead carbonate, and then the stripping slag is stripped by nitric acid to obtain high-grade gold concentrate; (6) dissolving the gold concentrate with hydrochloric acid and Cl2, reducing the gold solution with SO2 to obtain coarse gold powder, sending the coarse gold powder to electrolytic gold, and replacing the reduced mother liquor with zinc powder to obtain palladium platinum concentrate; (7) The insoluble residue produced by chlorination of gold concentrate is sent to recover tin and antimony. The feature of this method is that the traditional processes of smelting precious lead and pyrometallurgical refining are replaced by wet process, and the operations of sulfation roasting, distillation for selenium removal, leaching for copper removal and electrolytic refining of gold and silver are still retained. This improvement not only eliminates the harm of lead, shortens the treatment cycle, but also makes the direct recovery of gold and silver in anode mud from 73% and 865438 respectively.

The technological process of low-temperature oxidation roasting-wet treatment is shown in Figure 2. The main process is as follows: (1)648k low-temperature oxidation roasting oxidizes copper to CuO, Ag2Se to Ag2SeO3, and dilute sulfuric acid leaching transforms copper, selenium and tellurium into CuSO4, H2SO4 and H2SO4, which enter the solution and are separated; (2) firstly, the copper slag is chlorinated to separate gold, that is, NaClO3 is added into sulfuric acid medium, and gold, palladium and platinum are leached by stirring at the temperature of 353-363 K;

Then adjust the solution to pH 2 ~ 3, add oxalic acid to reduce gold, send the coarse gold powder to gold electrolysis or dissolution, and then extract and refine it. The mother liquor after reducing gold replaces palladium and platinum with zinc powder or recovers palladium and platinum by solvent extraction. (3) Under the conditions of pH8 and solid-liquid ratio 1: 8, the gold leaching residue was leached with a solution containing NaClO 3250 g/L for 3 hours, and silver generated Ag(SeO3)3- which entered the leaching solution. The leaching rate of silver is 99% ~ 99.8%, and the leaching solution contains about 50 g/L of silver, which is reduced by formaldehyde to obtain silver powder. The mother liquor can be recycled, and all the lead remains in the silver separation. It is 12% and16% higher than the traditional method; Short production cycle and low treatment cost; Eliminates the harmful effects of lead and ammonia on the operating environment.

The technological process of sulfation roasting-wet precipitation of gold and silver is shown in Figure 3, which is mainly composed of sulfation roasting distillation for selenium removal, dilute sulfuric acid leaching and leaching residue dissolution for gold separation. (1) Sulfated roasting and distillation to remove selenium: sulfuric acid roasting: anode mud = 1: 1, 573K hours, 823 ~ 873 K hours. The absorbed selenium is reduced to obtain crude selenium. (2) Dilute sulfuric acid leaching: leaching the distilled selenium residue with a solution containing sulfuric acid 1.5mol/L at a solid-liquid ratio of 1:( 12 ~ 15) at a temperature of 353 ~ 363 K for 2 hours, with a copper leaching rate of 99% and a silver leaching rate of 99%. Replacing the leaching solution with copper to obtain sponge silver. (3) Dissolving leaching residue to separate gold: leaching gold-bearing leaching residue produced by leaching lead and tellurium from dilute sulfuric acid leaching residue with NaClO3 solution, leaching for 4 hours with 3 times excess solution at H2SO4 1.5 mol/L, NaCl 2 mol/L, solid-liquid ratio L: 10 and 353-363 K, and leaching.

Flotation Enrichment of Gold and Silver Both China and Japan use flotation to enrich gold and silver from copper anode slime. The method in our country is to grind the anode slime after copper and selenium removal, and then flotation. Iron filings are added to replace silver in flotation, sulfuric acid is added to adjust the pH of the solution at 348 ~ 353 K, metaphosphoric acid is added to inhibit gangue and lead, ethylene glycol, turpentine or methyl isobutyl methanol are used as foaming agents, and butyl xanthate or black powder is used as collectors. Flotation in weak acid medium containing 200 g/L sulfuric acid. Concentrate is obtained through primary roughing, secondary scavenging and secondary cleaning. The recovery rates of gold and silver reached 95.5% and 97.4% respectively, and 90% of lead remained in tailings. The selected concentrate is generally 50% of the original anode slime. Crude silver anode plate is obtained by smelting concentrate with soda ash, and pure silver is obtained by electrolysis.

Sumitomo method is a method used by Sumitomo Metal Mining Company of Japan. After drying, the copper anode mud was put into a 673K roasting furnace for oxidation roasting. After feeding, the furnace was heated to 793K uniformly, then quickly to 973K, and the temperature was kept at 65438 0 h. After fine grinding, the roasted sand was leached with concentrated sulfuric acid at a temperature of 353K and a solid-liquid ratio of 65438 0: 5 for 3 h.

The process flow of wet treatment is shown in Figure 4. The main process is as follows: (1) dilute sulfuric acid and air (or oxygen) oxidation leaching to remove copper, and the copper removal solution returns to copper electrolysis; (2) chlorine gas and sodium chlorate are used as oxidants in the copper slag, and only selenium and tellurium in the copper slag are leached by controlling the dosage of the oxidant, namely leaching potential, while gold, silver, palladium and platinum are not leached, and the leaching solution is sent to recover selenium and tellurium; (3) leaching silver from leaching residue with NH. Oh, or not. S0, sending the silver leaching solution to silver for refining; (4) After removing lead from silver leaching residue with HNO3, dissolve gold with NaClO3 or Cl2 and hydrochloric acid, and send the gold solution to gold refining.