Study On The Microbial Solidification And Engineering Properties Of Cadmium-contaminated Red Cla

With the rapid development of China’s economy,the problem of heavy metal pollution is becoming more and more serious.The concentration of cadmium pollution in some areas of Guizhou has reached the level of severe pollution.The treatment of heavy metals involves a multi-disciplinary field,and microbial induced carbonate deposition（MICP）is a new application in microbial metallogeny.Its basic principle is to use bacteria that can produce urease to induce urea hydrolysis to generate carbonate and hydroxide plasma,and react with added calcium ions or free metal ions in soil to form carbonate precipitation and achieve the purpose of fixing heavy metals.In addition to adsorbing and wrapping the free heavy metal ions in the soil during the deposition process,the generated carbonate precipitation can also cement the soil particles and improve the mechanical properties of the soil.This technology provides a new way for the remediation of contaminated soil.In this paper,guiyang red clay was selected,the heavy metal pollution ion was Cadmium(Cd²⁺),and the microorganism was Bacillus pasteuris.Through indoor geotechnical tests,the physical and mechanical properties and environmental effects of contaminated red clay were studied under different concentrations of Cadmium ion,the dosage of activated carbon and different curing ages.The solidification mechanism of contaminated red clay by microorganism was analyzed by SEM and XRD.The main contents and conclusions of the study are as follows:（1）Cadmium ion has great biological toxicity to Bacillus pasteuris.When the cadmium ion concentration reaches 700mg/L and 1000mg/L,the bacteria has no obvious logarithmic growth phase,the bacteria has lost activity,and the OD value has no obvious change.（2）The results of basic physical and mechanical experiments show that cadmium ion decreases the dry density of soil and increases the liquid-plastic limit of soil,resulting in the increase of soil pore ratio.MICP technology increases the dry density of soil and reduces the plastic limit and pore ratio of soil fluid.With the increase of cadmium ion concentration,the unlateralized compressive strength decreased from 120.9k Pa to 63.77k Pa,and the unlateralized compressive strength increased by 1.66～1.94 times after microbial curing.The optimal curing days were 14days and activated carbon content was 10%.（3）The toxicity leaching test shows that the concentration of cadmium ion leached in soil increases with the increase of cadmium ion content,and the concentration after microbial curing is far less than the limit requirements set by the toxicity identification standard（GB5085.3-2007）.When the concentration of cadmium ion in soil is 100mg/kg,the concentration of cadmium ion leached is reduced to 0.002mg/L.In line with"surface water environmental quality standard"classⅱstandard 0.005mg/L.The BCR test shows that MICP reduces the migration of cadmium ions in soil,and the morphology of cadmium ions in the samples is mainly transformed from weak acid state and reducible state to residue state.（4）Scanning electron microscopy and X-ray diffraction experiments show that with the increase of cadmium ion concentration,the red clay particles become loose,and the pores gradually become larger.After microbial mineralization,the soil particles can effectively cement and fill the pores.The composition of basic sediment in soil is different from that in bacterial liquid.The sedimentary products formed in solution are more complex,including various mixtures of Ca_0.67Cd_0.33CO₃,Mg_0.06Ca_0.94CO₃,Mg_0.03Ca_0.97CO₃ and Cd CO₃,while in soil,the sedimentary products are mainly Ca CO₃ and Cd CO₃.