Theoretical Calculation And Experimental Research On The Surface Oxidation Mechanism Of Pyrite With Different Faces

Pyrite(Fe S₂)is one of the most common metal sulfide minerals in nature.Due to the more suitable band gap,pyrite shows excellent semiconductor and optical properties,and the physical and chemical properties of pyrite materials with different crystal faces will be different.The most common surfaces of pyrite are(100),(110),(111)and(210).Among them,the low-energy surface will show stronger stability,and the high-energy surface will have stronger electrical conductivity and optical properties.And so on,these series of properties make pyrite one of the photoelectric power materials that have attracted much attention in recent years,and it has great potential for development.But also due to widespread existence,when exposed to air or water environment,pyrite is very easy to be oxidized by the oxidant in the surrounding environment.The oxidation rate of pyrite with different crystal faces is different,and it is harmful after natural circulation process.It grows like a snowball,and eventually forms acid mine wastewater polluting the environment,affecting the health of animals and plants,and destroying the ecological balance.At the same time,the property of easy oxidation also limits the scope of application of pyrite on each crystal plane as a semiconductor material.Therefore,whether it is from the perspective of environmental protection or the perspective of green economy,studying the oxidation process of pyrite,especially familiarizing with the formation mechanisms and laws of pyrite oxidation products of different crystal planes,will be useful for exploring the control of acid mine wastewater pollution from the source.Methods and expanding the locality of pyrite as a functional material provide a scientific basis with more practical significance and reference value.In this thesis,first-principles calculations based on density functional theory are combined with chemical experiments and multiple characterization methods to study the surface oxidation mechanism of pyrite with different crystal planes.DFT calculation results show that among several common crystal planes of pyrite,the surface energy of(100)plane is the lowest,and the surface energy of(210)plane is the highest,which is more active and reacts with oxidizing substances in the surrounding environment.Through the construction and calculation of the O₂molecular adsorption model,it can be seen that whether it is a low-energy surface or a high-energy surface,when O₂is adsorbed on its surface,it will preferentially interact with the Fe atoms on the surface;but what makes difference is that on the Fe S₂(210)surface,due to the exposure of Fe atoms with lower coordination numbers,O₂will also interact with it more strongly,making the oxidation process faster than(100)planes,and the adsorption of O₂will increase As a result,part of the surface structure of(210)is reorganized and Fe-O-O-Fe bond is produced.At the same time,S atom will also produce new substances due to changes in electronic states.The results of electrochemical experiments show that the open circuit potential of the Fe S₂(210)electrode is significantly lower than that of the Fe S₂(100).After Tafel curve,CV and EIS tests,all parameters correspond to the surface energy calculation results,that is,the(210)type has higher surface energy than(100)type and is more prone to oxidation reaction.According to CV,it can be seen that the intensity of Fe S₂oxidation reaction in the former is higher than that in the latter.Through the analysis of the results of chemical leaching experiments,it can be seen that the oxidation rate of pyrite in the Fe S₂(210)group is increased by about 1.7times compared with the Fe S₂(100)experimental group.The detection of sulfur-containing intermediate products shows that the crystal faces are also different.It will cause differences in the production stages of various sulfites,and the p H change diagram shows that no matter what kind of crystal plane,when the oxidation reaction occurs,the steps of generating H⁺occur simultaneously.In the entire oxidation reaction process,FT-IR,XPS and other surface analysis techniques were used to characterize and analyze the pyrite samples,the results show that the surface of(210)-type pyrite is exposed to more reactive and more reactive 4-coordination Fe than the surface of(100)-type pyrite due to the existence of S defect sites,and the oxidation reaction on the surface will be faster.