In the light of antimonys character as an emerging,global pollutant,there is a real need to develop a better understanding of the geochemistry of antimony(Sb)in the weathering zone,beginning with its release from its predominant source,stibnite(Sb2S3).Oxidation dissolution kinetics of stibnite in the darkness has been studied in details.Sb2S3 as a semiconductor mineral,its dissolution and the fate of Sb(Ⅲ)released from Sb2S3 will be affected by photochemical reactions induced by sunlight,while nothing is known on the process.Here,the kinetics and mechanism of the photo-induced dissolution of Sb2S3 and important factors such as pH and dissolved oxygen on the photo oxidative dissolution of Sb2S3(s)were studied.A qualitative mechanism was proposed to describe the dissolution reaction under various ambient conditions,namely,light/darkness and aerobic/anaerobic.The simulation experiments were conducted by a photochemical reactor,a 500 W Xe lamp(λmax = 400-70 nm)was used as simulated sunlight source.250 mL suspensions with 0.2 g/L of Sb2S3 were magnetically stirred and about 1 mL of aliquots was taken from the reactor at intervals for subsequent Sb(tot)and Sb(Ⅲ)concentration analysis using hydride generation atomic fluorescence spectrometry(HG-AFS)after filtering.Some essential conclusions were drawn as follows: In the darkness and anaerobic condition,dissolution rate of Sb2S3 was almost zero.However,in the presence of oxygen,Sb2S3(s)can be readily dissolved.Protonation of Sb2S3 surface is the initial step of the reaction and formed thioantimonites,Sb(OH)x(SH)y3-x-y.In the presence of oxygen,the adsorption of O2 molecules onto the diprotonated Sb2S3(s)surface firstly oxidize S2-and then promoting the dissolution of antimony species from the Sb2S3.In addition,dissolution rate of Sb2S3 increased with pH,because more surface hydroxyl groups developed at Sb2S3 solid surface with the increase of pH weaken the bridging interstitial bonds through bond polarization,promoting the dissolution.In the irradiation of light,the dissolution rate of Sb2S3 was accelerated compared to in the darkness.Dissolved oxygen was the main working factor.In the presence of oxygen,upon photo irradiation,the positive holes migrate towards the surface Sb and S sites whereas the electrons are transferred to and combine with the adsorbed O2,converting the adsorbed oxygen molecules into hyperoxide ions,O2-,which is directly involved in the oxidation process.In the absence of oxygen,photo generated holes and.OH are main working oxidizers.