Srivastava Prashant, Singh Balwant, Angove Michael
Faculty of Agriculture, Food and Natural Resources, University of Sydney, NSW 2006, Australia.
J Colloid Interface Sci. 2005 Oct 1;290(1):28-38. doi: 10.1016/j.jcis.2005.04.036.
Polluted and contaminated soils can often contain more than one heavy metal species. It is possible that the behavior of a particular metal species in a soil system will be affected by the presence of other metals. In this study we have investigated the adsorption of Cd(II), Cu(II), Pb(II), and Zn(II) onto kaolinite in single- and multi-element systems as a function of pH and concentration, in a background solution of 0.01 M NaNO3. In adsorption edge experiments, the pH was varied from 3.5 to 10.0 with total metal concentration 133.3 microM in the single-element system and 33.3 microM each of Cd(II), Cu(II), Pb(II), and Zn(II) in the multi-element system. The value of pH50 (the pH at which 50% adsorption occurs) was found to follow the sequence Cu<Zn<Pb<Cd in single-element systems, but Pb<Cu<Zn<Cd in the multi-element system. Adsorption isotherms at pH 6.0 in the multi-element systems showed that there is competition among various metals for adsorption sites on kaolinite. The adsorption and potentiometric titrations data for various kaolinite-metal systems were modeled using an extended constant-capacitance surface complexation model that assumed an ion-exchange process below pH 7.0 and the formation of inner-sphere surface complexes at higher pH. Inner-sphere complexation was more dominant for the Cu(II) and Pb(II) systems.
受污染的土壤通常含有不止一种重金属物种。土壤系统中某一特定金属物种的行为可能会受到其他金属存在的影响。在本研究中，我们研究了在0.01 M NaNO₃背景溶液中，Cd(II)、Cu(II)、Pb(II)和Zn(II)在单元素和多元素体系中在高岭石上的吸附情况，该吸附情况是pH值和浓度的函数。在吸附边界实验中，单元素体系中pH值从3.5变化到10.0，总金属浓度为133.3 μM；多元素体系中Cd(II)、Cu(II)、Pb(II)和Zn(II)的浓度均为33.3 μM。发现在单元素体系中，pH50（发生50%吸附时的pH值）遵循Cu<Zn<Pb<Cd的顺序，但在多元素体系中为Pb<Cu<Zn<Cd。多元素体系中pH为6.0时的吸附等温线表明，各种金属之间存在对高岭石吸附位点的竞争。使用扩展的恒电容表面络合模型对各种高岭石-金属体系的吸附和电位滴定数据进行了建模，该模型假设在pH 7.0以下为离子交换过程，在较高pH值时形成内球表面络合物。内球络合在Cu(II)和Pb(II)体系中更为显著。
