Supergene Mobility And Transformation Process Mechanism Of Antimony In The Wastes Of Qinglong Antimony Mine In Guizhou Province

Antimony is a harmful metalloid,and mining activities are the main source of antimony entering the environmental medium.As the third largest antimony mine in China,the Qinglong antimony mine has accumulated a large amount of mine waste after decades of mining,and is located at an ecologically fragile karst area,the antimony in mine waste may directly contaminate the downstream surface water bodies and groundwater through weathering and migration,and accumulate in the soil and contaminate it,posing a potential threat to the surrounding ecological environment.Although some previous work has been carried out on Qinglong antimony mine waste,the process of Sb migration transformation in different mine wastes,the mechanism and its driving factors are not clear.Therefore,in this paper,we analyzed the mineral composition of Qinglong antimony mine waste by XRD,polarized light microscopy,SEM-EDS,EPMA,etc.We analyzed the main elements,Sb and As contents and morphology of mine waste and Sb and As contents of plants in Qinglong antimony mine waste.Finally,16 Sr RNA was used to analyze the composition of the inter-root microbial community of suitable plants and to explore the influence of geochemical parameters on the microbial community and the role of microorganisms on the migration and transformation of Sb.The main conclusions were as follows:(1)The main minerals in the fine-grained mine waste of Qinglong antimony mine are gypsum,quartz,kaolinite,Cristobalite,hematite,and the main antimony-containing minerals are stibnite and romeite.The main mineral composition in the block waste rock is not only the above minerals,but also a large amount of pyrite development,and the main antimony-containing phase is famatinite.In addition,antimony-containing minerals such as sulfur famatinite,chalcostibite,tetrahedrite,antimony element,valentinite,and tripuhyite are also found in the furnace slag.The presence of pyrite will accelerate the release of Sb in the mine environment,while the iron oxides generated by the oxidation of pyrite will adsorb Sb.(2)The content of Sb and As in all three mine wastes from the Qinglong antimony mine seriously exceeds the risk control value of the second category of construction land in China.From the perspective of comprehensive resource utilization,the recovery and utilization of Sb in slag and tailings can be considered.The mineral and chemical composition of mine wastes and the state of Sb and As deposition govern their migration and transformation.BCR sequential extraction results showed that Sb and As existed mainly in the residue state,followed by the reducible state in the three mine wastes.The four speciation of Sb in mine waste,f1-f4,correspond to the adsorbed fraction of clay minerals,the iron oxide bound fraction,the organic matter bound state and some antimony-containing sulfides,as well as the antimony-containing sulfides and antimonate minerals and antimony oxides that have not been completely extracted.Both Sb and As in the weak acid extractable state in the tailings account for a considerable content,and the ecological risk should not be neglected.(3)Analysis of the vertical characteristics of Sb and As in the slag profile revealed that Sb and As were released by oxidation and migrated downward under surface weathering and leaching,and were later transformed into reducible states by iron oxide adsorption at a certain depth.The Sb and As in the suitable plants of the antimony mine in Qinglong are significantly higher than those in the surrounding plants,and there is a risk of entering the human body through the food chain.From the Sb and As contents in plants and mine wastes,plants have obvious characteristics of stress absorption of metalloids,and plants can absorb a certain proportion of Sb and As from mine wastes.By comparing the Sb and As enrichment and transport characteristics of different plants,it was found that clover can be used as a pioneer plant to fix metalloids in the abandoned antimony mine.(4)The most abundant phylum in all bacterial samples was Proteobacteria,followed by Bacteroidota,Acidobacteriota and Actinobacteriota.The composition of the rhizosphere microbial communities of the three mine waste plants varied considerably,with microbial diversity being highest in waste rock,second highest in tailings and lowest in slag.High Sb and As contents may reduce microbial diversity,and other geochemical parameters also affect microbial community composition and species diversity.Actinobacteriota and Arthrobacter are important taxa for vegetation restoration and adaptive ecosystem construction in antimony mining areas.As the main bacterial species of antimony oxidizing bacteria in mine wastes,γ-Proteobacteria and α-Proteobacteria will participate in the process of Sb oxidation in mine wastes,which can accelerate the release of Sb from mine wastes but reduce the toxicity of Sb in the environment.(5)The migration transformation process and mechanism of Sb in the waste of antimony mines in Qinglong were summarized.The dissolution of antimony-containing minerals is strongly influenced by p H,and in addition,the presence of pyrite will greatly accelerate the oxidative dissolution of pyroxene and promote Sb release.In addition to downward leaching,the oxidized dissolved Sb will be adsorbed by clay minerals,iron oxides,etc.and combined with Ca2+ and Fe3+to form insoluble antimonate minerals,which will again fix Sb in the mine environment.In the migration and transformation process of antimony,pyrite,secondary oxide of iron,and microbial action all play an important role.