长江三角洲地区典型土壤对铅的吸附及其与有机质、pH和温度的关系

INFLUENCES OF SOIL ORGANIC MATTER, pH AND TEMPERATURE ON Pb SORPTION BY FOUR SOILS IN YANGTZE RIVER DELTA

采用批平衡方法实验研究了长江三角洲地区4种典型土壤对Pb的吸附、解吸行为及有机质和温度对Pb吸附的影响,并运用热力学参数K°、ΔG°、ΔH°和ΔS°解释了土壤Pb的吸附机理。结果表明,在本实验条件下,Pb在土壤上的吸附过程表现出明显的非线性,符合Freundlich模型。土壤Pb吸附Kf值大小为:滩潮土(石质淡色潮湿雏形土)(3816dm3kg-1)>乌黄土(底潜铁聚水耕人为土)(1984dm3kg-1)>青紫泥(普通潜育水耕人为土)(1030dm3kg-1)>黄泥砂土(铁聚潜育水耕人为土)(348dm3kg-1)。去除有机质后的土壤对Pb的吸附量降低,解吸率升高。吸附反应热力学表明,K°和ΔS°随温度升高而增大,ΔG°随温度升高而降低。ΔG°为负值,表明Pb吸附反应为自发反应,ΔH°为正值表明土壤Pb吸附为吸热反应。乌黄土、青紫泥和滩潮土对铅吸附的主要作用力为化学键力,黄泥砂土为范德华力和偶极间力。Pb在土壤上的解吸过程存在明显的滞后现象。pH、碳酸钙含量和平衡浓度越高,滞后系数越大,这可能与在高pH和高碳酸钙含量时,Pb与土壤形成难解吸内圈配位物有关。

Laboratory batch experiments were carried out to study Pb sorption desorption by four soils typical of the Yangtze River Delta in China. Thermodynamic parameters, like K°, ΔG°, ΔH° and ΔS°, were used to explain mechanism of the sorption. Results show that under the conditions of the experiment （two temperature treatments, 25±0.5℃ and 35±0.5℃） Pb sorption and desorption displayed nonlinear curves that fitted the Freundlich isotherm. The sorption Kfvalues of the four soils followed an order of Lithic Ochri-Aquic Cambosols （3 816 dm3 kg-1） 〉 Endogleyic Feaccumulic Stagnic Anthrosols （1 984 dm3 kg-1） 〉 Typic Gleyic Stagnic Anthrosols （1 030 dm3 kg-1） 〉 Fe-accumulic Gleyic Stagnic Anthrosols （348 dm3 kg-1）. In soils with organic matter removed, Pb sorption capacity decreased, but desorption rate increased. The K and ΔS° values increased with temperature, while ΔG° values decreased with temperature. The negative values of ΔG° suggested that Pb sorption was a spontaneous process. The positive ΔH° values indicated that Pb sorption was an endothermic process. Chemical bonding force is the major force in Pb sorption by Endogleyic Fe-accumulic Stagnic Anthrosols, Typic Gleyic Stagnic Anthrosols and Lithic Ochri-Aquic Cambosols, and Van Der Waals Force and dipole bonding force in Feaccumulic Gleyic Stagnic Anthrosols. Apparent hysteresis in Pb sorption-desorption was observed and varied from soil to soil, and the higher the pH, calcium carbonate content and equilibrium concentration, the higher the hysteresis index, which may be attributed to the formation of inner-sphere Pb sorption complex （less reversible） and precipitation of lead carbonate.