Study On Atmospheric Oxidation Leaching Mechanism Of Arsenopyrite In Acid Solution

As one of primary auriferous sulfides,arsenopyrite has an adverse influence on conventional gold leaching process with cyanide and thiosulfate.Besides,there still exist many controversial research findings with respect to atmospheric oxidation leaching mechanism of arsenopyrite in acid solution,therefore it is of great significance for the comprehensive utilization of complicated sulphidic gold-bearing refractory ores to study acid oxidation behaviors and leaching mechanism of arsenopyrite at ambient pressure.In this work,the effects of oxidants,leaching temperature,sulfuric acid concentration and mechanical activation pretreatment on oxidation leaching behaviors of arsenopyrite in sulfuric acid medium were studied.In addition,the mechanism of arsenopyrite oxidation leaching in acid conditions and mechanical activation to improve arsenopyrite reactivity also was investigated by means of X-ray diffraction(XRD),scanning electron microscope-energy dispersive spectrometer(SEM-EDS),X-ray photoelectron spectroscopy(XPS)and electrochemical measurement technologies,such as:open circuit potential(OCP),electrochemical impedance spectroscopy(EIS)and polarization curves.The leaching kinetic experiments results of arsenopyrite indicated that adding Fe2(SO4)3,HNO3 and H2O2 into sulfuric acid solution can significantly promote the acid oxidation leaching of arsenopyrite.Under the optimized experimental conditions,the leaching rate of asrenopyrite in H2SO4-Fe2(SO4)3,H2SO4-HNO3 and H2SO4-H2O2 was increased from 6.24%to 12.47%,83.02%and 58.33%compared to sulfuric acid solution,respectively.In H2SO4-H2O2 solution,the oxidation dissolution rate was mainly controlled by H2O2 concentration in later stage reaction as a result of the catalytic decomposition of H2O2 was accelerated by ions of Fe,As elements generated in the course of arsenopyrite leaching.Futhermore,ethylene glycol(EG)can significantly inhabit the decomposition of H2O2,which in turn facilitate the oxidation leaching of arsenopyrite.And the optimal addition of ethylene glycol was 5%,the decomposition rate of H2O2 reduced by around 70%while the leaching rate of arsenopyrite increased from 47.13%without EG to 81.70%with an addition of 5%ethylene glycol in H2SO4-H2O2 solution.Mechanical activation pretreatment can not only reduce particle size and increase the specific surface area of arsenopyrite,but also result in refining the grain and increasing the disordered degree of arsenopyrite crystal structure.What's more,As on arsenopyrite surface also was partially oxidized via mechanical activation pretreatment,which will greatly improve the reactivity of arsenopyrite.Moreover,the leaching rate of arsenopyrite milled 5 h was up to 54.46%,which increased by around 42%compared with counterpart of untreated arsenopyrite.However,arsenopyrite pretreated by mechanical activation can be completely leached in H2SO4-HNO3 and H2SO4-H2O2 sulution with 5%ethylene glycol.Electrochemical study demonstrated that passive layer formulated as Fe1-xAs1-yS was easily on the surface of arsenopyrite owing to the different migration rate of Fe,As and S elements,which will obviously hinder the further oxidation leaching of arsenopyrite in sulfuric acid medium.The dissolution rate of arsenopyrite was enhanced with redox potential of leaching system.Nevertheless,jarosite passive film will be generated during the reaction when the scanning voltage rised to around 1 V(vs.saturated Ag/AgCl).