| Generally,a large number of industrial tailings are produced during the mining of minerals,and most of these tailings are mainly sulfide minerals.Among them,pyrite(FeS2)is the most abundant and most common,and arsenopyrite(FeAsS)is the most important arsenic-containing mineral in tailings.When exposed to the environment,sulfide minerals such as pyrite and arsenopyrite will be oxidized by weathering and produce acid mine drainage(AMD),which not only forms sulfuric acid,but also forms highly toxic tailings containing arsenic.This leads to the acidification of large areas of rivers and lakes,which causing many serious environmental problems and threatening human health.Therefore,in order to effectively prevent AMD and protect the ecological environment,this paper studied the surface oxidation mechanism of pyrite and arsenopyrite in the co-existence of O2 and H2O via first-principles calculations.The first part:Firstly,the FeS2(001)surface crystal structure was constructed,and then,the adsorption of water molecules and oxygen molecules was studied.On this basis,the oxidation reaction path of FeS2(001)surface under the condition of pure oxygen and under the co-existence of oxygen-water was studied respectively.Under pure oxygen conditions,dissociation and adsorption of O2 are the most stable at the S–S site,which also provides evidence for the final migration of O atoms to the S site.Taking pure oxygen conditions as a comparison,under the co-existence of O2 and H2O,two possible surface oxidation reaction mechanisms were investigated and determined,including the continuous reaction with oxygen and water.Finally,the surface sulfur was completely oxidized to SO42-.At the same time,Fe–H2O2 species were found during the oxidation reaction.In addition,the source of oxygen in the sulfate produced by the oxidation of the pyrite surface was explored,and the two proposed mechanisms were consistent with the results of isotope experiments.The second part:Firstiy,the FeAsS(001)surface crystal structure was constructed,the adsorption of oxygen molecules on the surface was studied,and a possible adsorption form of O2 was provided.This form of O2 was fully activated.Through calculations,O2 dissociates and adsorbs to adjacent Assites with a very low energy barrier,confirming that the experimentally obtained surface Assites is more likely to be oxidized than S sites.Therefore,based on the structure of O2 dissociative adsorption,two possible surface oxidation mechanisms had been determined,which include continuous reactions with oxygen and water.Finally,the surface arsenic was oxidized to H3AsO4,and the surface sulfur is completely oxidized to SO42-.The oxidation reaction mechanism of FeS2(001)and FeAsS(001)surface were studied in this article,which will provide a theoretical reference for AMD prevention and mine flotation. |
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