| Study and analysis had been carried out on the relevant archives and papers about comprehensive processing of lead anodic slime, which was one of the main material for silver production. A new hydrometallurgical procedure for lead anodic slime under ambient temperature and weak oxidation circumstance had been provided based on the comparison of forth and flaw of most kinds of pyrometallurgical, hydrometallurgical and mixed procedures and processes. Experiments and testing results of the new procedure on scale from lab to semi-industrial production showed that:1,After about two weeks of storage, crude lead anodic slime could be oxidized, the precious metals and other elements would then be effectively separated by chloride acid leaching process under the conditions of ambient temperature, 5N concentration of chloride acid, liquid to solid ratio of 4:1 and leaching for 3 hours, less than 2 percent of silver and 4 percent of lead could be leached into liquid, at least 99 percent of antimony, 99 percent of bismuth and 84 percent of copper, however, could be leached out respectively.2,Lead and antimony, which would be vaporized in pyrometallurgical process, could be successfully recovered in form of lead sulfate and antimony oxychloride by hydrometallurgical processes of alkaline transformation of leaching slag, resolution in nitric acid, deposition in sulfuric acid, and leaching liquid hydrolysis respectively.3,Lead anodic slime employed in experiments mainly came from Yunnan province, with up to 10 percent of arsenic contained in it. Most of arsenic were leached into the acid liquid and then transformed into hydrolyzate of antimony, which would affect the quality of antimony oxychloride. Experiments showed that leaching the hydrolyzate in sodium hydroxide solution under the condition of ambient temperature, liquid to solid ratio of 12:1 and terminal pH value reaching 10.0 would decrease the arsenic contained from 13% to less than 2%, and meanwhile improve tenor of antimony oxychloride from 55% to 64%, further processes included recycling sodium hydroxide solution with calcium hydroxide and arsenic deposition in form of calcium arsenite.4,In order to prevent loss of silver, process of substituting sponge lead for silver in chloride acid leaching liquid before hydrolysis process had been employed and silver loss less than 10 mg/L was guaranteed. The used sponge lead could be recycled trough the procedure of chloride acid leaching, refinement in saturated sodium chloride solution and substitutional reaction with iron powder, and reused in next round.5,After separation of lead trough nitric acid solution, silver riched in the slag could then be extracted into liquid phase by sodium thiosulfate leaching process under the condition of ambient temperature, 250 g/L concentration of sodium thiosulfate, 20 g/L concentration of sodium sulfite anhydro, liquid to solid ratio of 10:1 and leaching for 1 hours. The leaching liquid could be recycled after silver deposition by sodium sulfide, and the black slag of silver sulfide could then be transformed to silver powder with silver concentration higher than 99.5 percent through processes of nitric acid solution, chloride acid deposition and sugar reduction. Drying, reductive melting and foundry were the final procedure for silver ingot production, with close control, silver reaching grade 2 to 1 of national standard could be guaranteed.6,The processes such as substitution of silver by sponge lead, alkaline transformation, lead resolution by recycled nitric acid, silver leaching by sodium thiosulfate and sodium sulfite anhydro had been analysed on the base of experiments and industrial practice, relevant instructions had been built.To sum up, the new procedure, which had the advantages of high extraction rate of valuable metal, simple control, less toxic waste ejection, reaction under ambient temperature and lower cost, was suitable for comprehensive processing of lead anodic slime in most metallurgical enterprises of all kinds of scales. |
PDF Full Text Request