Cu(Ⅱ)对红壤吸附Cr(Ⅵ)的影响

Effect of Cu(Ⅱ) on Adsorption of Cr(Ⅵ) by Red Soils

选择3种红壤研究了Cu(Ⅱ)对土壤吸附CrO42-的影响,结果表明Cu(Ⅱ)显著增加了土壤对CrO42-的吸附量,Cu(Ⅱ)对CrO42-吸附的影响程度随着Cu(Ⅱ)加入量的增加和体系pH的升高而增加。3种土壤对CrO42-的吸附量及Cu(Ⅱ)对土壤吸附CrO42-影响的大小顺序为:广西红壤>湖南红壤>江西红壤,这与这些土壤游离氧化铁和游离氧化铝含量的大小顺序基本一致。Cu(Ⅱ)不仅增加土壤对CrO42-的吸附量,在铜存在下土壤吸附的CrO42-的解吸量也高于对照体系中的,但解吸增量(加铜体系与对照体系之间解吸量的差值)比吸附增量(加铜体系与对照体系之间吸附量的差值)低得多,说明Cu(Ⅱ)对CrO42-在土壤中吸附的促进作用机制涉及静电作用、专性吸附和表面共沉淀。不同土壤中,不同机制对Cu(Ⅱ)促进CrO42-吸附的相对贡献不同,广西红壤中静电吸附的贡献很小;而在江西红壤和湖南红壤中,由于铜的吸附导致土壤表面正电荷增加使土壤对CrO42-静电吸附量增加是铜增加CrO42-吸附的重要原因之一。铜的促进作用增加了红壤对CrO42-的吸附量,降低了CrO42-在土壤中的活动性。

Three red soils collected from the south of China were used to study the effect of Cu（ Ⅱ ） on CrO4^2- adsorption by the soils. Results showed that the presence of Cu（ Ⅱ） led to the increase in CrO4^2- adsorption, and the extent of the effect increased with the increase in the amount of Cu（ Ⅱ） added and the rise in pH. The amount of CrO4^2- adsorbed and the effect of Cu（ Ⅱ ） on CrO4^2- adsorption by the soils followed the same order： the soil from Guangxi 〉 the soil from Hunan 〉 the soil from Jiangxi. The presence of Cu（ Ⅱ ） increased not only the adsorption of CrO4^2-, but also the desorption of pre-adsorbed CrO4^2-. However, the increment in CrO4^2- desorption was lower than that of CrO4^2-adsorption, suggesting that the enhancement mechanisms of Cu（ Ⅱ） on CrO4^2- adsorption by the soils involved electrostatic attraction, specific adsorption and formation of surface co-precipitates. The specific adsorption of Cu（ Ⅱ ） on the soil increased the positive surface charge and surface potential and thus resulted in the increase in CrO4^2- adsorption through electrostatic attraction. The relative contribution of different mechanisms to CrO4^2- adsorption changed with location of the soils. In the soil from Guangxi, the specific adsorption and the formation of surface co-precipitates were predominant mechanisms. While, in the soils from Hunan and Jiangxi, enhanced electrostatic adsorption of CrO4^2- due to Cu（Ⅱ ） adsorption was an important mechanism in addition to specific adsorption and the formation of surface co-precipitates. The effect of Cu（ Ⅱ ） on surface potential also increased with the rise of pH and this was one of the reasons for the increase of Cu（ Ⅱ ） enhancement with rising pH. The enhancement of Cu（Ⅱ ） increased the amount of CrO4^2-adsorbed by the soils and reduced its mobility in the soils.