Adsorption Characteristics Of Rice Husk Boichar And Its Effect To Remediate Soil Polluted By Heavy Metal Cadmium

In this experiment,the removal of cadmium from aqueous solution by biochar derived from rice husk was investigated.Batch adsorption experiments were performed to investigate the effect of initial pH,ionic strength on the removal of cadmium by biochar.The adsorption characteristics of cadmium by biochar was studied by fitting the isotherm equation,thermodynamic equation and kinetic models and comparing the changes of surface functional groups,mineral composition and surface morphology of bio char before and after adsorption.The effect of biochar application on cadmium transformation in brown soil was studied by measuring the content of different cadmium form,pH,organic matter and surface charge of soil.The effect of biochar application on the cadmium uptake by baby bokchoi was studied by measuring the cadmium contents in underground and aboveground of baby bokchoi every 10 days with a pot experiment.The bioaccumulation factor of cadmium in underground and the translocation factor of cadmium from underground to aboveground were also calculated.The main research results are as follows:(1)The Freundlich isothermal adsorption model was fitable to describe the cadmium adsorption by biochar,and the main adsorption mechanism was non-uniform and multi-layer adsorption,and it was spontaneous exothermic reaction at low temperature.The pseudo-second-order kinetics equation could better reflect the complex effect of the multiple adsorption mechanism between biochar and cadmium.Cadmium was adsorbed on biochar mainly by electrostatic attraction and ion exchange by surface active groups,oxygen-containing functional groups and alkaline salts on the surface.(2)The contents of exchangeable form cadmium fraction significantly decreased and the organic bound form cadmium and residual cadmium extensively increased with the increase of biochar application(P<0.05).Compared with the control treatment,the soil pH,organic matter and pH dependent charge significant increased with the increase of biochar application amount.Significant negative correlation between exchangeable form cadmium and soil pH was found(P<0.01).There were negative correlation between Fe and Mn oxides bound form of cadmium and soil pH(P<0.05),and there are significant positive correlation between organic bound formcadmium and soil pH,and residual form of cadmium and soil pH(P<0.01).(3)The cadmium contents in aboveground of baby bokchoi for the 1%,3%,and 5%biochar application decreased 8.86%,64.22%,and 68.40%,respectively compared with no biochar addition,and the cadmium contents in underground decreased 11.0%,57.9%,and 60.6%,respectively.The cadmium content in the cell wall increased with the increase of the amount of biochar applied,while the cadmium content in the cell soluble fraction and the organelle decreased.The cadmium bioaccumulation factor in underground decreased 0.01～1.26 and the cadmium translocation factor from underground to aboveground decreased 0.22～0.32.Thus,5%biochar application should be considered a suitable soil amendment for cadmium.