Study Of Gold Tailings Treatment And Stabilization By Microbial Mineralization Combined With Stratified Minerals

Cyanide tailings(CT)were hazardous solid wastes produced during the gold smelting process,which not only have fine particle size and loose nature,but also contained a large amount of toxic heavy metals,which caused great damage to the surrounding environment of the mine area by long-term stockpiling.The treatment of cyanide tailings using microbial induced calcium precipitation(MICP)technology can not only effectively fixed the toxic heavy metals in cyanide tailing,but also reduced the risk of dust spreading pollution.However,this technique also suffered from slow mineralization rate and uniformity of cured blocks.In this study,we conducted cyanide tailing curing and long-term stabilization experiments by screening montmorillonite as MICP strengthening additives with layered minerals as the research object.The results of the study are as follows:(1)The auxiliary screening experiments showed that among the five minerals,the addition of montmorillonite could improve the microbial activity and mineralization precipitation,and had good adsorption of heavy metal Pb²⁺,so montmorillonite was screened as the MICP enhancement auxiliary.The buffering property of montmorillonite can effectively protect microbial growth in acidic,alkaline or high colloid concentration environment to improve urease activity and mineralization yield in the tailings of MICP process.(2)The solidification experiments of cyanide tailings showed that the addition of 5%montmorillonite could increase the unconfined compressive strength(UCS)of the bio-cemented blocks by 32.5%,and the maximum UCS value was reached up to 1.11 MPa.The leaching rates of Pb,Cu,Cr and Zn were reduced by 88.79%,60.56%,87.18%and42.85%,respectively,and the morphology of heavy metals changed from the exchangeable state to the carbonate bound state.Scanning electron microscopy(SEM)results showed that fusiform clusters of crystals appeared between the cured tailings particles,and infrared transform spectroscopy(FT-IR)and X-ray diffraction(XRD)results confirmed that calcium carbonate crystals,calcite and spherulite,were produced between the MICP-treated tailings particles.The addition of desiccated stone resulted in more compact connections between the curing body particles and a more uniform overall structure.The calcium carbonate produced throughout the process improved the mechanical strength of the cured body and immobilized the heavy metals in the lattice.(3)The wet-dry,freeze-thaw cycle experiments showed that after 21 wet-dry,freeze-thaw cycles,the p H and dry density of the cured specimens decreased,the effectiveness of heavy metal Pb increased,and the carbonate bound state fraction decreased.Based on the long-term view,most of the heavy metals Pb in the specimens did not precipitate out,which proved that the MICP technique was effective in immobilizing heavy metals.In summary,this study successfully achieved the biocementation of cyanide tailings using montmorillonite in concert with the MICP technology.Physically,the curing block's compressive strength was improved by using the cementing property of calcium carbonate and the auxiliary effect of montmorillonite to weaken the risk of tailing drifting pollution caused by wind erosion;chemically,the generated calcium carbonate and montmorillonite immobilized and adsorbed the heavy metals in the tailing in the lattice,reducing the migration of heavy metals;based on the stabilization assessment results,the curing of cyanide tailing by using montmorillonite with MICP technology had Based on the results of the stabilization assessment,the use of montmorillonite with MICP technology to solidify the cyanide tailing have a certain long-term stability,achieving the purpose of double control of heavy metal pollution and wind erosion spread of tailing.