In-situ Mineralized Stabilization Of Heavy Metal Cadmium Mineralization In Tailings By Carbonate Mineralized Bacteria And Its Mechanism

The non-ferrous metal mining and dressing industry is one of the main sources of heavy metal pollution.A large number of tailings discharged from this kind of metal are easy to release heavy metals,thus polluting the soil and water surroundings.Microbially induced carbonate precipitation(MICP),as a more environmentally-friendly method with much lower cost,has become one of the research hotspots in heavy metal mineralization technology.This study took the x’nonferrous metal tailings as the research object,deeply explored the mineralization efficiency and influence of heavy metal cadmium(Cd)mineralization in tailings induced by the carbonate mineralized bacterial consortium,and revealed the mechanism and microecological effect of biomineralization in a systematical manner.Firstly,a stable,urease-producing consortium UPC(composed of Sporosarcina,norank_f_Bacillaceae,and unclassified_f_Bacillaceae)was constructed successfully,which exhibited the good adaptability to a wide range of environmental conditions.The column test was used to explore the effect of UCP on the in-situ mineralization of heavy metal Cd2+in tailings.It revealed that uniform,and stable mineralization in the tailings column occurred when bacterial concentration was 1×108 cfu·mL-1,bacterial retention time 3 hours,concentration of mineralization solution 0.25 mol·L-1,and flow rate 1.5 mL·min-1.In such circumstances,the mineralization rate of Cd2+reached as high as 80.7%.Bioineralization mechanism of Cd2+ in tailings induced by UPC was researched through Scanning Electron Microscope-Energy Dispersive Spectrometer(SEM-EDS)and other methods.It was found that the adsorption of UPC on tailings conformed to the pseudo-second-order kinetic and Freundlich isotherm model,and-CH3,-CH2,C-N/N-H and-COO’ play the main role in the adsorption.Besides,mineralized products(Ca0.67,Cd0.33)CO3 and calcite phases were generated on the surface of the bacteria which was served as the nucleation sites,and then tailings particles were coated and cemented.All of these would lead to the mineralization of Cd2+effectively inhibit or delay the release of Cd2+.Meanwhile,the study found that kaolin,illite,pyrite,quartz,calcite,and dolomite in tailings could promote the mineralization of Cd2+and to be agglomerated to varying degrees,and could also regulate the morphology of the mineralized products.Furthermore,calcite and dolomite,which were similar to the crystal form of the mineralized product,had the highest efficiency in promoting Cd2+mineralization and could be better agglomerated.The microecological effect of UPC mineralized heavy metals in tailings was explored through metagenomic analysis and other methods.It was found that the pH of acidic tailings can be raised to neutral or weakly alkaline by biomineralization,while the pH of alkaline tailings has little change,reduce the redox potential,porosity and bacterial diversity of tailings,and make UPC became the dominant bacteria.After mineralization,the relative abundance of urease genes,such as ureC,and the sulfur reduction genes,including fsr,sat,cysC,cysH,and cysI,was increased,while the relative abundance of sulfur oxidation genes,such as suoX,sqr,fccA,and fccB,was decreased.This was mainly due to the addition of UPC,the growth in the relative abundance of indigenous bacteria such as Lysinibacillus containing urease gene,and the reduction of sulfur oxidizing bacteria in the original tailings such as Thiobacillus.This study would provide a fundamental theory for the future in-situ mineralization and stabilization of heavy metal pollutions in tailings and being of great significance for the promotion of source control technology of heavy metals.