Study On Recovery Silver From Refractory Zinc Leaching Residue Of Baiying

Up to now, the silver from refractory zinc leach residues was unable to be recovered satisfactorily. More and more slags have being pile up derictly, not only causing waste of precious metals silver resources, but also bringing hazards to the environment. In order to change this situation, this paper mainly has researched zinc leaching residues from one zinc smelter enterprise of Baiyin Non-ferrous Group Co., LTD, Baiyin city, Gansu Province, to explore the possibility of recovery of silver from these residues through the flotation processing.The chemical compositions of the slag were badly complicated, mainly being mixed polymers made up of silicate and sulfate, components of which seriouslly adsorb each other. At the same time, the particle sizes of the residue was very fine and even the particle sizes of the one after the roasting was more finer, of which-0.034mm was more than83%, which was suitable for flotating derictly without grinding. The silver content in the residue is proximately267.0g/t, of which silver was manifested that there were many phase forms, such as silver sulfate, nature silver, silver chloride, silver sulfide, silver oxide and so on, and that64.74%silver was in plumbojarosite, that was directly unable to recover by the flotation.Experimental study indicated that adopting the roasting pretreatment combined flotation process can be successfully obtained the good silver concentrate with the grade of silver5334.Og/t and silver recovery rate71.41%. The best process combination was followed:1) Best roasting pretreatment conditions:the roasting atmosphere was general air environment, the roating temperature was650℃, the roasting time was2.5h, the cooling model was natural cooling. During the industrial production,500-650℃was the adjustable temperature range of the roasting pretreatment;2) Optimum flotation process and reagent regime:the best process was made of one rougher, one concentrating, one scavenger and the middles after reflotating back to the rougher. The optimal reagent regime:the rougher were flotation carrier OC3000g/t, activator sodium sulphide3000g/t, major collector ammonium dibutyl dithiophosphate770g/t, minor collector GC79.5g/t, frother BK20150g/t; the concentrate were collector ammonium dibutyl dithiophosphate385g/t, frother BK20150g/t; the scavenger were activator sodium sulphide1500g/t, collector ammonium dibutyl dithiophosphate385g/t, frother BK20150g/t; the middles reprocessing were activator sodium sulphide500g/t, collector ammonium dibutyl dithiophosphate200g/t, frother BK20150g/t;3) The best flotation machanical conditions were the strong mixing and the strong inflation. The optimum conditions in laboratory were that flotator impeller speed was up to2100r/min and the charged valve was fully open.Mechanism analysis on roasting pretreatment showed that the essence of zinc leaching residue roasting pretreatment was the thermal decomposition (thermolysis) of the residue. Thermal decomposition was able to destruct and destroy plumbojarosite workframe, and after650℃roasting process, about20%H3O-jarosite and0.35%jarosite born in zinc leaching residue almost disappeared. According to thermal weightlessness condition of the residue, the thermal decomposition of zinc leaching residue following the temperature from low to high was the dehydration stage (50～145℃), dehydroxylation stage (300～425℃), the desulfurization stage (530～680℃) and deoxygenation stage (super-700℃), in which dehydroxylation stage and desulfurization stage were the key. Adopting the Kissinger method and the Flynn-Wall-Ozawa method, apparent activation energies of dehydroxylation stage and desulfurization stage were644.7kJ/mol and742.1kJ/mol respectively.