| The increasing request of heavy metal resource(Cu,Pb,Zn,Cr and so on)promotes the exploring and mining industry,which is responsible for massive mining tailings.Metal sulfides are usually disposed in air and oxidized by microbes to form acid mine drainage(AMD),meanwhile release heavy toxic metals to water and soil.Microbe could largely enhance the oxidation of sulfides and accelerate the formation of AMD.Furthermore,the bioleaching of microbial oxidation of sulfide has been widely used in the hydrometallurgical industry.In the AMD environment,iron is usually precipitated as iron sulfates and iron oxides,such as jarosite,schwertmannite and ferrihydrite.Because of their metastability,these iron minerals commonly transformed to stable iron oxides such as goethite and hematite.In the Fe/Mn-rich environment,stable Fe oxides and Mn oxides could remove heavy metals from water by coprecipitation or surface adsorption.Thus,understanding the mechanism of the microbial oxidation of sulfides and the surface reaction of Fe/Mn minerals contributes to the revealing of element cycle,mineral transformation and the environmental implication,which could guide environmental remediation of mine tailings.Based on the advanced progress in this area,by means of field sampling and investigation as well as mimic experiments in the lab,this study focused on the microbial oxidation of sulfide,the mineralogical transformation of iron sulfate and the surface reaction and environmental implications of stable Fe/Mn oxides.Some conclusions are listed below:1.The mechanism of the collaborative effects of Acidithiobacillus ferrooxidans and ferrous ions on the oxidation of chalcopyrite and accelerating the release of Cu was revealed in this study,and a conceptual model of the evolution of elements and the oxidation of sulfides was proposed in this study.By conducting the mimic experiments on the oxidation of chalcopyrite by A.ferrooxidans and ferrous ions,secondary minerals,element value and the evolution of sulfur species was analyzed.These results showed that:(1)In the presence of additional ferrous ions,A.ferrooxidans prefer to oxidize Fe2+ to chalcopyrite to acquire energy;(2)the intermediate minerals are identified as jarosite and schwertmannite.The evolution of sulfur is S2-/S22-?Sn2-/S0?SO32-?SO42-;(3)STXM results showed that Cu enriched in the the EPS surrounding the bacteria provides the evidence for the survival of A.ferrooxidans cells in high Cu concentration;(4)A conceptual model was proposed by comparing the abiotic oxidation and microbial oxidation of chalpyrite,which could provide a new insight into the hydrometallurgical application and environmental remediation;(5)Furthermore,the mechanism of mineralogical transformation from schwertmannite to Na-jarosite under the synthesis condition was investigated.2.Geochemical distribution of As and Zn controlled by Fe/Mn oxides in ferromanganese ducrust was investigated and an evolution model was proposed.We collected the ferroomanganse ducrusts samples and identified these ferromanganese ducrusts as a composition of goethite,hematite,pyrolusite,and hetaerolite,and As and Zn in these minerals are distributed different.The results showed that:(1)As is enriched in Mn oxides.The ratio of the contents of As in pyrolusite and hematite is about 5:1;(2)The highest content of As is in the Mn-substituted hematite micro-bands;(3)EXAFS results revealed that As is bound on the surface of Fe/Mn minerals in bidentate binuclear bridging complexes;(4)The pyrolusite is closely encrusted with fine hematite grains,which could protect the retained As from out fluids.All these results provide valuable insights for understanding the geochemical behavior of heavy metals and environmental remediation.3.The substitution of Mn induced the structural alteration of goethite and the mechanism of the enhanced adsorption of Pb by Mn-subsituted goethite was disclosed by EXAFS.In this study,Mn-substituted goethites with different contents of Mn were synthesized and the mineral structure was indentified with SR-XRD,as well as the surface characteristics and the adsorption behavior of Pb.The results indicated that:(1)Mn is incorporated as Mn(III)in goethite and caused the decrease of a and c and the increase of b;(2)The particle size is decreased with the increase of Mn content,the enhanced adsorption of Pb is caused not only by the increase of SSA,but also the surface complexes at the Mn site;(3)EXAFS results indicated that Pb is bounded on the Mn site with RPb-Fe=3.47 A.This study helps us to understand the adsorption mechanism of heavy metals on metal-substituted goethite,and also provides guide to developing Mn-goethite as a potential material in environmental remediation.In conclusions,from the field sample analysis and mimic experiments,we studied the oxidation of sulfides,mineralogical transformation of iron sulfates,the retain of heavy metals by Fe/Mn minerals and the environmental implication of Mn-substituted goethite and itspotential application.This research revealed the beginning of sulfide oxidation,mineral transformation and surface reaction of Fe/Mn minerals,as well as the environmental effect through mineralogy.Furthermore,we developed a new model for surface reactions of minerals and the evolution and distribution of elements,which help us to understand the geochemical cycle of elements in poly-metal mine environment.This work would also promote the development of geomicrobiology,mineralogy,geochemistry and environmental research. |
PDF Full Text Request