Study On The Passivation Remediation Of Cadmium-contaminated Brown Soil By Magnesium-modified Biochar

Biochar adsorption method is a potentially widespread application and economical carbon-rich adsorbent for heavy metal pollution.However,the use of the biochar material alone has problems such as low density,difficult molding,and difficult separation of particles from water,which limits its application.In order to improve the adsorption capacity of cadmium by biochar,modification treatment of biochar can change the pore structure and surface characteristics of biochar,improve its adsorption capacity and the potential of environmental restoration applications.In this paper,300?and 600? biochar were prepared using coconut shell and peanut shell as raw materials,and magnesium modified biochar was prepared by chemical impregnation.By means of X-ray diffraction(XRD),Fourier transform(FTIR)and adsorption experiments of Cd2+ on biochar and MgCl2 modified biochar,the adsorption energy of Cd2+ on biochar before and after modification and at different pyrolysis temperatures was compared,and the mechanism of repair was discussed.At the same time,in this study,the brown soil of farmland in Rizhao City,Shandong Province,contaminated with cadmium reagents was used as the research object.Two kinds of repairing agents were used:peanut shell biochar and magnesium modified peanut shell biochar as repair agents.Bioavailability research.The effects of two biochar materials on brown soil pH,brown soil available cadmium,total brown soil cadmium,spinach growth status,and spinach uptake of heavy metals were studied through soil cultivation experiments and pot experiments.Remediation effect of biochar materials on heavy metal cadmium contaminated soil,and the possible remediation mechanism was explored through correlation analysis between parameters.The main findings are as follows:(1)Compared with unmodified biochar,MgCl2 improved the specific surface area and total pore volume of modified biochar,and increased the pH value,ash content,polarity and hydrophilicity of unmodified biochar.The results of SEM-EDS,BET and XRD showed that MgO has been successfully loaded on biochar.The biochar adsorbent obtained by pyrolysis of a mixture of MgCl2 and biochar prepreg is a composite material composed of MgO crystals and primary biochar.The characteristic peaks of MgO modified biochar and unmodified biochar are similar by FTIR,which shows that MgO particles have little effect on the types of organic functional groups in biochar.(2)The pseudo-second-order kinetics and Langmuir isothermal adsorption equation can better describe the adsorption process of Cd2+ by biochar and magnesium-modified biochar.Thermodynamics shows that the adsorption process of Cd2+ by biochar and magnesium-modified biochar is an endothermic process at an ambient temperature of 298-318K.The higher the temperature,the better the performance of the adsorbent for improving the Cd2+ adsorption performance.In the initial pH range,magnesium-modified coconut shell biochar has a strong adsorption capacity for Cd2+.In the initial pH range,magnesium-modified peanut shell biochar has a strong adsorption capacity for Cd2+.Its adsorption rate varies with the initial pH.With the increase of pH,with the increase of pH,the adsorption of Cd2+ by the same adsorbent gradually reached equilibrium.The MgO particles on the surface of the modified material play an important role in the adsorption of Cd2+.The adsorption process is mainly based on chemical adsorption.(3)After applying biochar to brown soil under different treatments,the pH value of the soil can be effectively increased.In the case of exogenous pollution of brown soil,all types of biochar can effectively reduce the content of available Cd2+ in the soil,and it is directly proportional to the applied amount and pyrolysis temperature.Obviously,it may be because MgO is contained in biochar,which increases its alkalinity(4)The addition of peanut shell biochar and magnesium-modified biochar materials has improved the growth of spinach to a certain extent,and the quality and dry weight of spinach have been increased accordingly,while the root length of spinach has an inhibitory effect.Cadmium pollution has a significant stress on plant root growth After applying biochar in soil,cadmium has a more significant stress on root growth.Without the addition of heavy metal cadmium,the application of various biochars has different degrees of plant roots.Promotion effect.Magnesium-modified biochar can promote spinach growth better than native biochar,which is mainly related to the nature of biochar.The nutrient content of modified biochar is relatively high,which can better meet the needs of spinach growth when applied to the soil..In summary,magnesium-modified biochar has a better passivation and repair effect on heavy metal cadmium,and can be used as a passivation and repair technology model for cadmium exceeding the standard for brown soil for field application and promotion.