Trace elements competitive sorption

The enhancing effect of NaCl on Cd uptake was due to chloride complexation of Cd (Smolders et al., 1998). High salinity in soils increased the concentrations of chloride complexes of trace elements (such as CdCl or CdCl2°) in soil solution, which increased and correlated best with Cd uptake of both plant species as discussed above. In addition, salinity also affected plant root function, and Na competition with Cd for sorption sites in soil may be a possible contributor. 

I.I. Simultaneous Sorption of Trace Elements Few studies have been carried out on the competition in sorption of trace elements to soil components and soils. Competition in sorption between two or more trace elements is of paramount importance for understanding their relative affinity for a given sorbent. 

Benjamin and Leckie (1981) found a nearly complete lack of competition of Cd, Cu, Zn, and Pb for sorption sites of a noncrystalline Fe precipitate. The lack of competition of these cations may be related to low surface coverage and/or precipitation effects and only partially to the presence of different binding sites having high selectivity for specific trace element ions (Kretzschmar and Voegelin, 2001). 

Competitive sorption of trace elements to organic soil components has also been studied. Kinniburgh et al. (1996) demonstrated that Cd sorption on a humic acid was reduced by Ca, but in contrast, Cu sorption was poorly reduced. Mandel et al. (2000) showed clear competitive effects of Ca and Mg on Ni sorption to a soil fulvic acid. Many studies have showed evidence that there may be differences in competition between selected trace elements depending on the functional group composition of the humic substances (Kretzschmar and Voegelin, 2001). 

Effect of Time and Surface Coverage on Competitive Sorption Between Trace Elements and Organic or Inorganic Ligands... 

Most competitive sorption studies have been carried out adding the ions contemporaneously. In natural environments, however, it is more likely that the ions will come in contact with a sorbent sequentially (i.e., the solid is exposed to one ion first, with the second ion coming in contact with a solid at a later time). The sorption of trace elements in cationic or anionic form is strongly influenced by the order of addition of organic and inorganic ligands and trace elements on the sorbents. 

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