Environmental Behavior And Effect Of In-situ Immobilization Of Cadmium Contaminated Soil With Biochar

In the present study, biochars from straws of cotton were prepared at550-600℃by oxygen-limitedpyrolysis. Batch experiments were used to study the adsorption of Cd²⁺by the biochars to provide datarelevant to the remediation of cadmium contaminated soil. The objectives were to evaluate the abilitiesof biochars generated from cotton straws to adsorb Cd²⁺from aqueous solutions and to probe theadsorption mechanisms for Cd²⁺on the biochars. In addition, the field experiments were conducted withbiochar to evaluated environmental behavior and effect of in situ immobilization of cadmiumcontaminated soil with biochar. The main conclusions are shown as following:1) The adsorption of Cd²⁺on biochar can be fitted by Freundlich isotherm better than Langmuirisotherm. The maximum adsorption amounts of Cd²⁺at different temperatures are9.738mg·g^-1（288.15K）,10.14mg·g^-1（298.15K）,10.40mg·g^-1（308.15K） and10.71mg·g^-1（318.15K）, respectively. Thefree energies ΔG0is from-8.346to^-10.276kJ·mol^-1at different temperatures, indicating that theadsorption of Cd²⁺onto biochar is spontaneous and is an endothermic process. The adsorption processcan reach equilibrium in40minutes and can be fitted by pseudo second order kinetic model. The pH hasa significant effect on the adsorption of Cd²⁺on biochar in the pH range of2-8. The amount ofadsorption of Cd²⁺on biochar shows a reducing trend with the ionic strength increasing. XPS shows thathydroxyl groups （-C-OH） and carbonyl groups （-C=O） have participated in Cd²⁺sorption onto biochar.2) Compare with the unamended soil, biochar （5,10,20t·ha1） and its fermentation poultry manure（10t·ha1）and NPK fertilizer （0.6t·ha1） mixed treatments can significantly reduce the uptake andaccumulation of Cd in edible and root parts of Lactuca sativa L.. Cd concentrations in edible partsreduce by32.6%-54.8%, Cd concentrations in root parts decrease by14.4%-30.9%. Of all thetreatments, biochar and fermentation poultry manure mixed treatments have the best effect on reducingthe accumulation of Cd in edible and root parts of Lactuca sativa L.. Soil available Cd concentrations ofall the treatments significantly reduce by7.04%-21.85%compared with the control. Biochar singleapplication as well as20t·ha1biochar and NPK fertilizer mixed treatments increase the soil pH by0.03-0.25units, biochar and poultry manure mixed and5t·ha1biochar mix NPK fertilizer treatmentsreduce soil pH by0.04-0.14units compared with the control. There is highly significant positivecorrelation between Cd concentration in edible parts of Lactuca sativa L. and soil available Cdconcentration.3) Compare with the control, all the treatments can significantly increase soil catalase, urease andalkaline phosphatase by10.2%-34.9%,18.0%-38.5%and0.7%^-13.4%, respectively, and alsosignificantly increase soil ammonium nitrogen, nitrate nitrogen and available K by61.1%^-105.8%,64.6%-295.5%, and54.0%-212.5%, respectively. For the available P in the soil, compared with theunamended soil, only treatments of biochar mix fermentation poultry manure and the20t·ha1biocharmix NPK fertilizer hsve ignificantly improved by21.5%^-134.5%. Compare with the control, availableCu has decreased but available Mn has increased, while available Ca, Mg, Fe, Zn have risen from lowerthan the control to higher than the control with increasing of biochar application. Gene abundances inbiochar amended treatments show a little higher than the control, and from the similarity coefficient and DGGE UPGMA, biochar treatments maybe have impact on soil microbial community structure asincreasing of biochar application.