Effects Of Isomorphic Replacement On The Surface Reactivity Of Sphalerite And Pyrite

As an important carrier of nonferrous metals and rare dispersed element minerals,the surface reactivity and geochemical behavior of sulfide minerals have attracted wide attention.Sphalerite and pyrite are the most common sulfide minerals.Sphalerite is a mercurophilic sulfide mineral.The adsorption and fixation of mercury on sphalerite controls the geochemical behavior of mercury,and it has important application prospects in the treatment of man-made mercury pollution.The adsorption capacity and reaction mechanism of sphalerite towards Hg²⁺in water have been studied,but few reports have been reported on the performance and mechanism of the adsorption of gaseous Hg⁰ on sphalerite.The weathering of pyrite produces a large amount of acid mine wastewater?AMD?and heavy metal pollution.Therefore,the surface oxidation of pyrite is a research hotspot in mineralogy and related fields.The oxidation of pyrite produces hydroxyl radicals?^·OH?.^·OH has high redox potential and can oxidize environmental pollutants without selectivity,which restricts the migration,transformation and fate of related environmental substances.In nature,isomorphic substitution widely exists in sphalerite and pyrite structures,which may affect the physical and chemical properties and surface reactivity of minerals.Iron is the most common displacement ion in sphalerite.Although some studies have shown that iron displacement enhances the adsorption performance of sphalerite towards Hg²⁺,the extent and mechanism of its influence on the adsorption and fixation reactivity of gaseous Hg⁰ on sphalerite are still unclear.There are many transition metal ions in the structure of natural pyrite.The oxidation process of pyrite and the mechanism of producing^·OH have been studied,but the influence on the formation rate of^·OH during the oxidation process have not been paid attention to.For those reasons,this dissertation takes"the restriction of isomorphic substitution on the surface reactivity of sphalerite and pyrite"as the theme,takes synthesis?iron substitution?sphalerite and pyrite?cobalt,nickel and manganese substitution?as the research objects,and uses various modern spectroscopic techniques to investigate the effects of the typical isomorphic substitution on the crystal structure and surface physical and chemical properties of sphalerite and pyrite.The effects of sphalerite adsorbing gaseous Hg⁰ and pyrite acidic oxidation production^·OH simulation experiments were performed to discuss the above scientific issues,and the following understandings were obtained:1.The restricting of iron displacement on the adsorption of gaseous Hg⁰ on sphalerite.The substitution of Fe for zinc in sphalerite was accompanied by the co-substitution of O for S,which significantly affected the physical and chemical properties and surface reactivity of sphalerite.The co-displacement increased the Zn-S bond length on the surface of sphalerite and enhanced the magnetism of sphalerite.But the co-displacement decreased the oxidation and reduction temperature of sphalerite.The adsorption mechanism of sphalerite for gaseous Hg⁰ followed the Mars-Maessen mechanism,i.e.the fracture of surface Zn-S and the formation of Hg-S.Co-displacement reduced the bond strength of Zn-S on the surface of sphalerite,which improved the adsorption of gaseous Hg⁰ on sphalerite.In the simulated flue gas,the capacity of Fe-bearing sphalerite towards gaseous Hg⁰ was 4-5 times than that of pure sphalerite.and Fe-bearing sphalerite had better adsorption performance and recycling regeneration than other magnetic adsorbents.These results showed that Fe-bearing sphalerite had good application prospects in the field of gaseous Hg⁰pollution control of flue gas from coal-fired power plants.2.The restriction of isomorphic substitution on the production of^·OH by the oxidation of pyrite.Replacement ions,such as Co,Ni,Mn,delaied the growth of pyrite crystals,increased the bond length of Fe-S on the surface of pyrite,and made pyrite exposed more high-energy reaction surfaces.These substitution ions increased the specific surface area and electrical conductivity of pyrite and reduced the thermal stability of pyrite.In aerobic acidic aqueous solution,the rate of^·OH production?specific surface area standardization?of pure pyrite and pyrite doped with Co,Ni and Mn were1.30×10^-3,4.40×10^-3,1.29×10^-1 and 1.94×10^-3?mol L^-1 min^-1 g m^-2,respectively.These substitution ions significantly improved the electron transfer efficiency of pyrite,promoted the formation of intermediate product H₂O₂,and thus enhanced the production of^·OH by the oxidation of pyrite in aerobic acidic aqueous solution.The electron transfer efficiency of pyrite was improved by substitution ions.The order of effect was Co>Mn>Ni.The?111?surface of Ni-Py was high energy reaction surface,which promoted the oxidation of pyrite.The Fe³⁺in Mn-Py solution could significantly inhibit the formation of hydrogen H₂O₂.Therefore,the promotion of replacement ions on the^·OH production by the oxidation of pyrite was in the order of Co>Ni>Mn.The above research results will be helpful to the understanding and grasp of the geochemical behavior of sphalerite and pyrite.Thses results will also provide the theoretical basis for the application of the two minerals in environmental engineering.