Geochemical Form, Risk And Basis Of Microbial Remediation Of Heavy Metals In Lead - Contaminated Soils

In recent years, with the population growing and industrialization and urbanization expanding, the human demand for minerals increased, at the same time heavy metal pollution problems emerged, especially, the environmental pollution and human health problems caused by heavy metals, attract the attention of the people around the world and related concerned organizations. Therefore, how to solve the problem of heavy metal pollution has become the focus of national attention. In nature environment the metal elements in atmospheric dust, rain, rivers and other media, finally accumulate into the soil in various ways, and heavy metals in urban soil enter our living environment by human activity through the hand-mouth direct contact or other ways to enter the body, undermining people health. Research on heavy metal pollution in cities contribute to further understanding of the mechanism of heavy metals’release and transformation in the soil, and their toxicity, bioavailability, restoration measures, and impact on ecosystems and human health hazards, while it is important on potential ecological risk assessment and analysis of heavy metals exposure risk assessment,which will provide a theoretical basis and foundation to control heavy metals contamination.In this experiment, the study area is near a lead related factory in GuanzhongBasin. based on field survey and previous studies, diverse mix Samples were analyzed using Tessier sequential extraction method, for geochemical form distribution of heavy metals Pb, Zn, Cd, Cr, Cu, Sb. On the basis of six kinds of heavy metal activity coefficient (MF), the migration coefficient (MJ), potential ecological risk index (RI) and population health exposure risk studies.we studied the kinetic and thermodynamic experiments by using Bacillus Subtilis strain powder which is isolated and cultivated from a long term lead polluted industrial area with a certain concentration of lead, antimony ion solution. Then studied the mechanism of adsorption of microbial leaching on heavy metal elements, followed by simulation through soil leaching experiment of Bacillus Subtilis dry powder with lead ions and antimony ions in the contaminated soil, the study provide theoretical and technical foundation for the Bacillus Subtilis dry powder’s practical application. The main conclusions of this study are followed:(1)Through Tessier five-step extraction method of soil samples in this industrial zone and environmental risk assessment, it indicate that the distribution speciation of heavy metals Pb, Zn, Cd, Cr, Cu and Sb are quite different, Cd, Cr, Cu, Sb, Zn mainly exist in residual form, while Pb mainly present in Fe-Mn oxides bound and occupied the largest environmental mobility, Cr’s mobility is minimum. Potential ecological risk assessment showed that th risk of heavy metals in this area is very relatively high, heavy metals Pb, Cd, Sb have relatively high biological activity, Pb has the largrest biological activity, Cd has the biggest migration index.Environmental risk assessment showed that metal Cd and Cr in this area, their cancer risk on children and adults is no more than the middle level, but Cr exerts a greater non-cancer risk on children. The heavy metal Pb for both children and adults have a very significant non-cancer risk and moderate level of cancer risk, visiblely, heavy metal Pb is the most important environmental pollutants and health risk factors.(2)Based on the Multi-orthogonal design adsorption experiments that carried out by mixing the dry powder formulations of Bacillus with lead, and antimony ion solution.the study showed that Bacillus Subtilis dry powder formulation is an excellent lead, antimony ion biosorbents. By fitting an existing model calculations show that the correlation test and experiment more in line with the Freundlich isotherm model, Presudo-second-order kinetic model, Elovich equation is not suitable to describe the lead, antimony ions in Bacillus Subtilis biological adsorption model. Thermodynamic analysis shows that Bacillus Subtilis and lead, antimony ion adsorption process is a process of spontaneous adsorption. The lead adsorption is an endothermic chemical reaction; antimony adsorption is an exothermic reaction, while entropy of the lead and antimony ion adsorption is increasing.(3)The microbe leaching experiment that on Bacillus Subtilis dry powder and contaminated soil showed that with the increasing biomass of Bacillus Subtilis dry powder formulations added, the lead ion and antimony ions’s leaching extent accelerated.to some extent. Temperature rise is not conducive to soil leaching of metal ions.at the same tvme;Bacillus Subtiliswith its metabolitesis an excellent adsorbent whichwill promote the development of phytoremediation of the heavy metal pollution, extremely.