Adsorption Of Cd By Carbon-rich Material And Its Application In Remediation Of Soil Polluted By Cd

Heavy metal in farmland soil is threated to soil environmental health and safety of agricultural products,and furthermore damages human health.Meanwhile,organic wastes produced during the process of agricultural production and urban life are increasing year after year,and its output is huge,which under the pressure from the increase of population and the acceleration of urbanization.So,the rational disposal and resource utilization of organic waste is an urgent problem.In view of this,the biochar of lotus petiole?HBC?derived from lotus petiole and YM organic compost?YM?derived from sewage sludge and kitchen wastes were studed in this study.The adsorption mechanism of carbon rich material HBC and YM on Cd²⁺and their influence on Cd migration and morphological transformation in soil were explored.In addition,YM was applied to remediation the cadmium polluted farmland soil around mining areas.The results are as follows:?1?Optimal preparation temperature of HBC is 400?under the condition of hypoxia.Fourier infrared spectrum?FTIR?analysis,scanning electron microscope?SEM?analysis and elemental analysis found that HBC has developed porous structure and mass oxygen contained functional groups?-OH,COO-and C=O-?on the surface.Adsorption capacity of HBC for Cd²⁺in liquid was up to 23.0 mg/g under experimental conditions.The adsorption of Cd²⁺on HBC surface is a chemically dominated adsorption process which occured on the surface of porous media based on the fitting results of Freundlich isothermal adsorption model and quasi-secondary kinetic model.This adsorption process could be roughly divided into three stages:?1?Cd²⁺rapidly diffused to HBC surface from the solution affected by the force of concentration gradient.?2?Cd²⁺bonded to the HBC surface through ion exchange reaction and complexation with functional groups,meanwhile,Cd²⁺coprecipitated with metal oxide and carbonate from ash.?3?Cd²⁺diffused into the porous structure of HBC and had a cationic-?effect with the?electron structure that prevalent in the benzene ring.?2?High organic content?OM content 35.8%?and strong alkalinity?pH=7.92?are two remarkable characteristics of YM,and mass oxygen contained functional groups?-OH?-CH₂?on its surface confirmed by XPS and FTIR analysis.The results of XPS analysis and adsorption-desorption test showed that both obligate adsorption and electrostatic adsorption play important roles during adsorption process.Results of YM-soil culture experiment showed:YM improved the adsorbing performance of soil to Cd²⁺observably and enhanced the fixation potential of soil to Cd²⁺,which mechanism is the enhancement of obligate adsorption of soil improved by YM.?3?The results of soil remediation tests showed that both HBC and YM reduced the bioavailability of Cd in soil and impelled the transformation of Cd from acid-exchangeable form to reducible and residual form.In the soil-rice system,YM improved soil pH,CEC and SOM contents,and meanwhile decreased the content of Cd in brown rice?the lowest value is 0.183 mg/kg?.YM limited the transfer of Cd from soil to rice plants and improved the proportion of Cd in the roots of rice plants.Stepwise regression model showed that soil pH is the most key and major parameter among the factors?soil pH,soil Eh,SOM content,soil CEC content and dosing quantity of YM?that might affect the content of Cd in brown rice.YM promoted the healthy level of rice plants and realized the safety production of rice,and furthermore improved the safety utilization of polluted farmland soil with Cd.The common adsorption mechanism of HBC and YM:mass oxygen contained functional groups?-OH?COO-?,aromatic ring and carbonates are the key substances for the complexation,chemical precipitation and ion exchange with Cd²⁺on the surface of carbon-rich materials.Carbon-rich materials reduced the bioavailability of Cd in soil and impelled the transformation of Cd from unstable form to stable form observably.