Abstract:Pyrite (FeS2) is one of the common and important sulfide mineral that associates with gold，coal，graphite and valuable sulfide minerals (such as galena，sphalerite and chalcopyrite， etc.). The semiconductor property of pyrite play a crucial role in facilitating complex electrochemical reactions with flotation reagents，grinding media and oxygen during the grinding and flotation processing of pyrite. There is a strong correlation between pyrite floatability and electrochemical reactions. Hence it is essential to clarify the electrochemical behavior of pyrite surface for optimizing pyrite surface hydrophobicity during grinding and flotation processes. This paper provides an in-depth review of the adsorption mechanisms of typical pyrite flotation reagents，including collectors，activators and depressants，with a particular focus on the effects of dissolved oxygen (DO) concentration and slurry pH value. In this review，xanthate，copper sulfate (CuSO4) and lime (CaO) used as collectors，activators and depressants of pyrite，respectively are discussed in detail. Xanthate ions can be adsorbed on the pyrite surface through Fe sites by chemical reaction，forming iron xanthate. However，iron xanthate is not the only compound to make pyrite partcles hydrophobic. Xanthate can be easily oxidized to dixanthogen in the slurry containing oxygen. Subsequently，co-adsorption of dixanthogen generated by oxidation of xanthate can occur on the pyrite surface by intermolecular forces between xanthate radicals in dixanthogen and ferric xanthate complex. The mechanism of pyrite activation by copper ions (Cu2+) is attributed to ion exchange between ferrous and cupric ions along with the spontaneous reduction of Cu2+ into Cu+ and the oxidation of sulfur under slightly acidic conditions. In alkaline solutions，Cu2+ adsorbs quickly onto reactive surface sulfur sites where it is reduced to Cu+ via sulfur oxidation. The Cu(OH)2 overlayer is formed to cover pyrite surface as the Cu activation process proceeds. The depression mechanism of CaO is mainly attributed to the alkaline environment availability and the calcium species coverage. And the adsorbed calcium cations on the hydroxylated pyrite surface could complete their coordination shell layer surrounded by six ligand oxygens，causing the formation of hydrophilic hydrated calcium film on the pyrite surface and achieving the hydrophilization of pyrite. The pyrite oxidation mechanisms in the water and oxygen systems are discussed and the distribution characteristics of oxidation products on the pyrite surface under specific parameters are clarified. The important evidences are provided for hydrophobic species such as elemental sulfur (S0)，metal polysulfides (FeSn) or metal-deficient sulfides (Fe1-xS2) that are formed under moderately oxidizing potentials，resulting in collectorless flotation of pyrite. However， excessive oxidation leads to the generation of hydrophilic iron hydroxides (e.g.， Fe(OH)3) and sulphate (e.g.，SO42-) under the high slurry pH and/or potential，which reduce the floatability of pyrite particles. The balance between oxidation and hydrophobicity is a key factor in pyrite recovery. Special attention is directed to the grinding environment that can greatly influence electrochemical oxidation and reduction processes of pyrite surface. Various factors such as grinding media (typically steel or ceramic) and gas atmosphere (air，nitrogen，or oxygen) contribute to the extent of electrochemical reactions. Strong galvanic interactions between pyrite particles and grinding medias occur due to the difference in the residual potentials between pyrite particles and grinding medias，thereby accelerating oxidation reactions to occur on the surface of pyrite particles. Subsequently，the flotation behavior of pyrite is significantly affected by oxidation reactions on the surface of pyrite particles. This review systematically describes the electrochemical behavior of pyrite particle surface during grinding and flotation processing based on the research results in recent decades，which improves the basic knowledge of pyrite surface chemistry through fundamental electrochemical regulation and provides theoretical technical support for enhancing pyrite flotation separation.