Recovery Of Associated Au And Ag From Sphalerite Concentrate By Oxidizing Acid Leaching

Associated gold and silver in nonferrous metal mineral are important resourcesof precious metals, especially in polymetallic sulfide ore. These gold and silver are ofhigh value to the concentrator. Associated gold and silver in flotation sphaleriteconcentrate are usually recovered from the smelter slag. However the recovery ofgold and silver is not satisfactory, and environmental pollution is rather serious inconventional pyrometallurgical and hydrometallurgy process of sphalerite. Therefore,it is necessary to develop a low-cost and environmental-friendly technique by which ahigh recovery of gold, silver and other valuable elements can be obtained fromsphalerite concentrate.Firstly, the paper summarized current methods and research status ofhydrometallurgy of zinc, sulfur extraction, the extraction of gold and silver; then,according to the analysis of occurrence characteristics and series exploratoryexperiments, the oxidizing acid leaching process was applied on sphaleriteconcentrate at the first time. The optimum conditions of oxidizing acid leaching：leaching temperature85℃，liquid-solid ratio3:1, reaction time8h,stirring speed400rpm, the dosage of H2O2110%of the theoretical amount, dosage of sulfuric acid100%of theoretical amount and Fe3+0.04%of the theoretical amount. Under thisexperimental conditions, the zinc and sulfur leaching efficiency reached96.7%and92.8%respectively, the recovery rate of gold and silver in leaching slag wererespectively99.8%and49.3%.Sulfur in sphalerite concentrate was enriched in thedregs as the form of ordinary sulfur. The follow-up process of recovering gold andsilver from the leach residue and leach solution.Comparing extraction efficiency and other characteristics of various extractionsolvent, perchlorethylene used in this experiment as sulfur extraction agent. Theoptimum conditions of sulfur extraction experiment：extraction temperature95℃,extraction time10min, dosage of extraction solvent300%, stirring speed400r/min,the extraction efficiency of sulfur reached99.82%at this condition. Load organicphase cooled to room temperature can separate the organic phase and the sulfur, thenthe organic phase can be reused.Examining the leaching efficiency of gold and silver, compared to sodiumcyanide, the results demonstrated that the similar cyanide agent has apparent advantages. The optimal conditions of similarcyanide leaching test: normalatmospheric temperature, leaching time12h, liquid-solid ratio3:1, pH10, similarcyanide agent dosage0.04%, stirring speed400r/min. Under these conditions, theleaching efficiency of gold and silver are93.37%and88.83%respectively. Therecovery of the silver in the zinc sulfate solution was carried out by using ironreplacement, and the replacement optimum conditions were as follows: six times theamount of the theoretical amount of iron, replacement time75min, pH2.5. Under thiscondition the silver replacement efficiency can reach nearly100%.The gold and silver recoveries are93.37%and93.79%in the entire process, zincand sulfur recoveries are96.7%and92.8%.