淹水还原作用下土壤镉的吸附与解吸特征的初步探讨

Preliminary investigation on adsorption and desorption of Cd in soil with different reduction states

利用黄棕壤发育的水稻土(pH6.53),设置6个不同处理恒温(25±0.1)℃培养20d,初步探讨了3种还原强度土壤对Cd的吸附和解吸特征。试验数据显示:强度还原土壤,Eh和pH降低并稳定在-474mV和5.02水平,Cd吸附率由开始时的99.96%下降到94.70%,Cd解吸率平均为90.01%;中度还原土壤,Eh下降至-90mV左右,pH略有上升,Cd吸附率和解吸率平均分别为99.96%和66.09%;氧化态土壤的Eh、pH和Cd解吸率变化都比较小,平均分别为400.4mV、6.11和46.78%。此结果表明,处于不同还原状况下的土壤表面对Cd吸附和解吸有所差别;强度还原土壤对外源Cd的吸附率小于中度还原土壤对外源Cd的吸附率;土壤吸附外源Cd的解吸率,由大到小的次序依次为强度还原土壤,中度还原土壤,氧化状态土壤;还原程度越强,土壤对Cd的吸附率越低,Cd的解吸率也越高;还原条件下土壤Eh、pH、交换性亚铁和水溶性有机质含量是影响土壤Cd吸附和解吸的主要因素。

Cadmium adsorption and desorption are important processes to control its solubility and bioavailability in soils. In this study we report the adsorption and desorption of Cd under three different reduction states in a paddy soil developed from yellow brown soil. For the strongly reduced soil, the Eh and pH decreased and stabilized at -474 mV and 5.02. The percentage of adsorbed Cd was reduced from 99.96% to 94.70%. The average Cd desorption ratio was 90.01%. At the moderate reduction level, the soil Eh decreased to around -90 mV and pH increased slightly. The average percentage of adsorbed and desorbed Cd was respectively 99.96% and 66.09%. For the aerated soil there is a small change ofEh, pH and Cd desorption, whose average values were 400.4 mV, 6.11 and 46.78%, respectively. The results indicate that the adsorption and desorption of Cd in soils differed with reduction levels. The adsorption ratio of the adscititious Cd in the strongly reduced soil is less than that in the moderately reduced soil, whereas the desorption ratio of the adscititious Cd decreased with the following order： strongly reduced soil 〉 moderately reduced soil 〉 aerated soil. The stronger the reduction state, the lower adsorption and higher desorption ratios of Cd in the soil. In addition, Eh, pH, exchangeable Fe^2＋ and dissolved organic matter （DOM） are major factors to affect Cd adsorption and desorption in soils under the reduced soil condition.