不同温度下镉在典型农田土壤中的吸附动力学特征

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30 d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常数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。

Effects of Temperature on the Adsorption Kinetics of Cadmium in Typical Agricultural Soils

Adsorption is the initial process when heavy metals enter soil. Adsorption is important because it directly influences the bioavailability of heavy metals in soil. In this experiment, batch techniques were used to study Cd adsorption by 12 typical agricultural soils from China. The adsorption data were fitted using kinetic equations. The results showed that Cd adsorption could be divided into two steps regard- less of temperature ： fast reaction and slow reaction. At 25 ~C, Cd adsorption reached 72.69% of the soil＇s maximum adsorption capacity within the first 5 minutes of the reaction and 83.76% of the soil＇s maximum adsorption capacity within the first 30 minutes of the reaction. At 40 ~C, Cd adsorption reached 77.50% of the soil＇s maximum adsorption capacity within the first 5 minutes of the reaction and 87.02% of the soil＇s maximum adsorption capacity within the first 30 minutes of the reaction. Chemical adsorption was the main adsorption mechanism for the fast reaction, whereas physical adsorption was the main adsorption mechanism for the slow reaction. Furthermore, the whole reaction mainly de- pended on the fast reaction, which is attributed to chemical adsorption. The Elovich model best described Cd adsorption by these soils. The adsorption rate and amount of Cd adsorption were both greater for alkaline soils than for acid soils. High temperatures also increased the adsorption rate and the amount of Cd adsorption by the soils. The Cd adsorption rate was mainly affected by pH.