水稻土中重金属元素Cd、Pb的竞争吸附——以长株潭地区水稻土为例

Competitive adsorption of cadmium and lead in paddy soils:a case study of paddy soils in Changsha-Zhuzhou-Xiangtan area of Hunan Province

对中国南方的3个水稻土样品进行了Cd、Pb单一离子和混合离子吸附特点的研究。结果表明,3个水稻土样品中Cd、Pb的吸附特点都相似,Langmuir等温方程可很好地描述Cd、Pb的吸附等温线。3个土壤样品中,有较高pH值和较低有机物、CEC浓度、粘土含量、高岭石含量的2个土壤样品对Cd、Pb有较大的吸附量,且其等温吸附拟合的最大吸附量(B)也较大。在两组分混合溶液中,尽管共存离子的存在影响了土壤对单一离子的吸附,同时土壤对Cd的吸附在一定程度上受影响的程度大,但3个土壤样品都表现出对Pb有强的吸附能力。在3个土壤样品中,Langmuir等温方程中Pb的健合能常数(K)都大于Cd的健合能常数(K),混合溶液中的K值高于单一溶液的K值,表明2种金属离子对吸附位点的竞争提高了特定吸附位点的保持力,使金属离子在土壤中特定位点的吸附更加坚固。

In this paper,adsorption characteristics of Cd and Pb in three kinds of paddy soils in southern China were studied.The result showed that the sorption characteristics of Cd and Pb in paddy soils were similar,and their adsorption isotherms were all well described by Langmuir equation.Two soil samples with relatively high pH and comparatively low organic matter,CEC,clay content and kaolinite content had greater adsorption capability for Cd and Pb,as estimated by the maximum adsorption parameter（B） of the Langmuir equation.The presence of both metals reduced the tendency for either metal to be absorbed in soils;at the same time,Cd adsorption was affected to a greater extent than that of Pb,but all soils exhibited greater sorption capacity for Pb than for Cd.In three kinds of soils,the Langmuir binding strength parameter（K） was always greater for Pb than for Cd.Meanwhile,K value of binary solution was higher than single solution.This may indicate that the competition for adsorption sites promotes the retention of both metals at some specific adsorption sites,which can cause firm adsorption of metals in specific sites of soils.