稻草生物质炭对3种可变电荷土壤吸附Cd(Ⅱ)的影响

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

按土重的3%和5%向采自海南和广西的3种可变电荷土壤中添加由稻草制备的生物质炭,混合培养30d后用一次平衡法研究了生物质炭对土壤吸附Cd(Ⅱ)的影响及其与土壤表面电化学性质的关系,旨在阐明生物质炭促进可变电荷土壤吸附和固定Cd(Ⅱ)的机制。结果表明,添加稻草炭显著提高了3种土壤的阳离子交换量(CEC)和土壤pH,并使土壤胶体Zeta电位向负值方向位移。因此,添加稻草炭增加了土壤表面的负电荷量,土壤表面对Cd(Ⅱ)的吸附容量增强,使3种可变电荷土壤对Cd(Ⅱ)的吸附量增加,且Cd(Ⅱ)吸附量的增幅随稻草炭添加水平的提高而增加。Freundlich方程和Langmuir方程可以拟合3种土壤对Cd(Ⅱ)的吸附等温线,但Freundlich方程拟合效果更好,该方程表征吸附容量的参数k也随着稻草炭添加水平提高而增大。研究表明在pH3.0～5.0范围内,稻草炭均增加土壤对Cd(Ⅱ)的吸附量。添加稻草炭提高土壤pH,促进Cd(Ⅱ)的吸附,因为Cd(Ⅱ)的吸附量随pH升高而增加。解吸实验表明,添加稻草炭处理Cd(Ⅱ)的解吸量高于对照处理,说明生物质炭提高了土壤对Cd(Ⅱ)的静电吸附量。

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 bioehar. 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 bioehar 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 Freundlieh equation, which was related to adsorption capacity, also increased with increasing bioehar 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 bioehar 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