Evaluation Of Soil Heavy Metal Remediation Based On Kiwi Wood Biochar

Heavy metals concentrated in the soil are not easy to decompose,which causes the degradation of farmland soil fertility,affects the safe production of crops,and even threatening human health by accumulating in the human body through the food chain.Biochar is a carbon-rich solid substance obtained by pyrolysis of agricultural and forestry wastes.It has the characteristics of high specific surface area and strong adsorption capacity.After the biochar is applied into the soil,a series of reactions such as adsorption,precipitation,complexation and ion exchange occur with the heavy metals in the soil,which passivates the heavy metals in the soil and can be used to remediate the pollution of the soil environment.In this study,the waste kiwi branches were used as raw materials to derieved biochar.First,the affecting factors including initial concentration,adsorption time,initial pH,and sorbent dosage were investigated in batch experiments.The biochar before and after adsorption was characterized using scanning electron microscopy(SEM)and Fourier transform infrared spectroscopy(FTIR).The adsorption capacity of biochar for Cd2+,Pb2+and Zn2+from aquaculture wastewater and landfill leachate was tested.To lay the foundation for studying the immbolization effect of kiwi wood biochar on heavy metals in soil.Secondly,through soil incubation and pot experiments,set up 1%,2%and 4%of biochar addition,with no added biochar soil as a control to study the physicochemical properties of the soil,the bio availability of heavy metals,the leaching toxicity,the fractions of Cd,Pb and Zn,soil enzyme activity,mustard growth and absorption of heavy metals,are aimed to provide a theoretical basis for the resource recovery of waste kiwi pruning branches and the remediation potential of kiwi wood biochar to heavy metal pollution in smelters and mines contaminated soils.The main research results are as follows:(1)The kiwi wood biochar is alkaline,with a pH of 11.4,a specific surface area of 15.7m2·g-1,a porous structure,and rich surface functional groups.The optimal conditions for Cd2+,Pb2+,and Zn2+ adsorption were pH 4-6 with 120 min contact time(reached equilibrium.The optimal sorbent dosages were 4.0,3.0,4.0 g·L-1,and the maximal adsorption capacity was recorded at 9.35,65.9,36.8 mg·g-1,respectively.(2)The adsorption kinetics experiments showed that the Cd2+,Pb2+,and Zn2+adsorption onto biochar followed a pseudo second order model.Isothermal adsorption experiments showed that at 25?,the Langmuir equation was more suitable for the adsorption of Cd2+by biochar,and the theoretical maximum adsorption capacity was 13.1 mg·g-1.The adsorption characteristics of Cd2+were well described by the Langmuir equation with theoretical maximum adsorption capacity of 13.1mg·g-1,whereas the Freundlich equation was more appropriate for Pb2+ and Zn2+adsorption.Overall,the kiwi wood biochar shows higher adsorption performance and potential application in Cd2+,Pb2+,and Zn2+removal from wastewater.(3)With the increase of biochar dosage,the pH value,CEC,organic matter and enzyme activities(dehydrogenase,urease and sucrase)of FX and TG soils increased,the bio availability and leaching toxicity of heavy metals Cd,Pb,Zn reduced.BCR analysis showed that compared with the control soil,the maximum decreases in acid soluble fractions of Cd,Zn,and Pb in FX soil were 11.1%,13.3%,and 24.7%at 4%biochar addition.and that in TG soil were 7.67%,22.8%and 7.89%,respectively.Meanwhile,the residual fractions of Cd,Zn,and Pb in FX soil increased by 55.9%,7.14%,and 11.0%,respectively,and in TG soil increased by 23.7%,5.86%,and 10.0%,respectively.(4)The pot experiment showed that with the increase of biochar application,the contents of Cd,Pb and Zn in the soil of mustard root decreased,the biomass of mustard increased significantly,and the accumulation of heavy metals decreased significantly.Moreover,the addition of biochar increased the chlorophyll content,the enzyme activities of peroxidase(POD)and catalase(CAT),and reduced the content of malondialdehyde(MDA)in mustard plants.Therefore,on the one hand,the preparation of kiwi wood biochar is beneficial to the recycling of agricultural wastes.On the other hand,it is feasible to remediate heavy metals pollution in soil environment.