Study On The Effect And Stability Of Microbial Mineralization On Remediating Copper And Lead Contaminated Soil

With the rapid development of agricultural and industrial production in China,especially the increase of heavy metal emission enterprises,a large amount of wastes containing heavy metals are discharged into the natural environment,has caused serious environmental pollution problems.Heavy metals are not easy to be degraded,and they are easy to be concentrated in plants and animals,which seriously endanger the health and survival of various living things including humans.Therefore,it is urgent to find an effective and economical way to control heavy metal pollution.Based on the method of microbially induced carbonate precipitation(MICP),this article uses the inducer of Sporosarcina to repair copper and lead contaminated soil.Firstly,the growth characteristics of microorganisms under heavy metal environment were studied and domesticated;then,the repair effect of microbial mineralization method was evaluated through the repair experiment of heavy metals in water and soil respectively,and preliminary investigation of repair mechanism was conducted through field emission scanning electron microscopy and X-ray diffraction;followed studying the stability of heavy metal contaminated soil in acid solution,freeze-thaw cycle and high temperature environment,the main factors affecting the stability were compared and analyzed;Finally,the soil column leaching test was used to simulate the effect of actual rainfall conditions on the stability of contaminated soil.The following conclusions are obtained in this paper.(1)With the increase of heavy metal ion concentration,the number of bacterial cells gradually decreased and the growth lag period gradually increased during the culture process of Sporosarcina.When the concentration of Cu2+ and Pb2+ are about 1000mg/L and 1300mg/L respectively,the bacteria lost their activity and no longer appear fast growth period.A:fter bacterial acclimatization,the tolerance of microorganisms to Cu2+ and Pb2+ increased to about 1300mg/L and 1550mg/L.(2)When repair Cu2+and Pb2+pollution in the water,the removal rate is highest with the concentration of urea and calcium chloride in the reaction liquid is 1.5mol/L.The average removal rate of Cu2+ is 70.03%after repair of one time;the average removal rate of Pb2+ is 89.32%after repair of one time;when repair Cu2+and Pb2+ pollution in the soils,the exchangeable state contents of copper and lead contaminated soils was reduced by 46.68%and 61.12%respectively,and the carbonate bound state contents were increased by 26.58%and 40.68%respectively,residual content increased by 9.16%and 12.74%respectively compared with unrepaired contaminated soils after repair of three times.(3)Field emission scanning electron microscopy and X-ray diffractometry showed that the most of the Cu2+ repair sediments are in the form of CaCO3,and the most of the Pb2+ repair sediments are co-precipitation of CaCO3 and PbCO3.CaCO3 can incorporate Cu2+ into the sediments or the gap between the crystal by surface adsorp,so that the fixation of Cu2+ is achieved.On the one hand,Pb2+ can generate fine PbCO3 adsorbed on the surface of CaCO3 crystals,on the other hand,CaCO3 can also incorporate Pb2+ into the sediment or the gap between the crystal by surface adsorption,so that the fixation of Pb2+ is achieved.(4)Immersed in nitric acid solution with pH 2.5 lasted for 60 days,the exchangeable state contents account were increased by 20.02%and 24.22%respectively in the repaired copper and lead contaminated soil;in the freeze-thaw cycle lasted for 60 days,the exchangeable state contents account were increased by 7.5%and 6.2%respectively in the repaired copper and lead contaminated soil;in the high temperature of 12O?lasted for 60 days,the exchangeable state contents account were increased by 9.56%and 15.3%respectively in the repaired copper and lead contaminated soil.(5)After acid rain leaching,compared with unrepaired contaminated soils,the contents of heavy metals filtered were reduced by 16.29%and 15.69%respectively,and the average exchangeable state content were reduced by 24.32%and 37.68%in the repaired contaminated soil.