Effect of Biochar from Rice Straw on Adsorption of Cd(II)by Variable Charge Soils

Three variable charge soils collected from Hainan and Guangxi Provinces were incubated with biochar from rice straw for 30 days,and then the batch method was used to investigate the effect of the biochar on adsorption of Cd(Ⅱ)by these soils as related to soil surface electrochemical properties to elucidate the mechanisms for the enhancements of adsorption and fixation of Cd(Ⅱ)by the biochar.Results showed that the biochar induced a remarkable increase in soil CEC and pH and shift of soil Zeta potential to negative direction.The adsorption of Cd(Ⅱ)was increased with increasing biochar added.Freundlich and Langmuir equations can be used to fit the adsorption isotherms for Cd(Ⅱ),but Freundlich equation fitted the adsorption isotherms better.The parameter k in Freundlich equation,which was related to adsorption capacity,also increased with increasing biochar added.The adsorption of Cd(Ⅱ)by the soils was increased by the incorporation of the biochar in the pH ranged from 3.0 to 5.0.The addition of biochar increased the soil pH and the adsorption of Cd(Ⅱ)consequently.Results obtained from desorption experiment showed that the amount of Cd(Ⅱ)desorbed for the treatments with biochar added was greater than that for control,suggesting that the biochar increased the electrostatic adsorption of Cd(Ⅱ)by the soils.