Research progress in bioleaching of pyrrhotite and associated valuable metals
In order to solve the problem of efficient and green recycling of pyrrhotite and its associated valuable metals preferably,the research progress on the bioleaching of pyrrhotite and its associated valuable metals were summarized. Firstly,the chemical leachability of pyrrhotite was analyzed. Secondly,the process and mechanism of bioleaching of pyrrhotite were introduced. Finally,the effects of bacterial types,breeding and domestication,inoculation amount,pH,slurry concentration,and ore pretreatment on the biological leaching process were summarized. The recovery process of associated metals such as nickel and gold in pyrrhotite was analyzed. The results show that oxidation of pyrrhotite under acidic conditions mainly depends on the cyclic reaction on the surface sulfur rich layer. The bioleaching of pyrrhotite mainly includes three mechanisms:indirect effect,indirect contact effect,and direct contact effect. The essence of leaching reaction is the oxidation of iron and sulfur,and the galvanic effect,extracellular polymeric substances(EPS),the jarosite and sulfur passivation layer also have important impacts on bioleaching. Different bacterial strains have different leaching effects on pyrrhotite. Increasing bacterial inoculation,reducing slurry concentration properly,maintaining a low pH value,domesticating the selected bacterial strains and using sulfuric acid for pretreatment of gangue can improve the effectiveness of bioleaching on pyrrhotite. Also,the bioleaching of pyrrhotite has positive leaching effect on its associated valuable metals,such as nickel,cobalt,and gold,with a leaching rate of over 80％.The research emphasis on the bioleaching of pyrrhotite should focus on the regulation mechanism of passivation layer in the future,inhibition or controlling the formation of the surface passivation layer through various regulatory measures,the balance regulation of iron content in bioleaching solution and the resource and high-value utilization of iron. Besides,laboratory research is gradually applied to industrial production.
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