EDTA on montmorillonite

K6nya, J., and N. M. Nagy. 1998. The effect of complex-forming agent (EDTA) on the exchange of manganese ions on calcium-montmorillonite. I. Reaction scheme and Ca-montmorillonite/Na2EDTA system. Coll. Surf. 136 297-308. 

FIGURE 2.11 The ratio of cCa aCa can be plotted as a function of the concentration of Ca2+ on montmorillonite (the exchange isotherm of a calcium-hydrogen-sodium ion exchange) with and without the EDTA complex-forming agent. (Reprinted from Konya and Nagy 1998, with permission from Elsevier.)... 

Nagy, N. M., and J. Kdnya. 1998. Ion exchange processes of lead and cobalt ions on the surface of calcium-montmorillonite in the presence of complex forming agents. I. The effect of EDTA on the sorption of lead and cobalt ion on calcium-montmorillonite. Coll. Surf. 137 231-242. 

The effect of a complex-forming agent on the cation-exchange processes of montmorillonite is well demonstrated in calcium-montmorillonite, manganese(II) ion, and the sodium salt of the ethylene diamine tetraacetic acid (EDTA) system (K6nya and Nagy 1998 Konya et al. 1998). The reactions are illustrated in Figure 2.9. 

The sorption of calcium ions is as expected at low pH values, the calcium ions, present as Ca2+, sorb, as in the absence of a complex-forming agent the quantity of the sorbed calcium increases when the pH increases. At pH values where negative Ca-EDTA complexes are already formed and the concentration of hydrated Ca2+ ions decreases, the sorption of calcium on the surface of montmorillonite also decreases. 

FIGURE2.14 The equivalent fractions of lead ion on the surface of montmorillonite and the ratios of different lead-EDTA complexes in the solution at Pb EDTA =1 1. (Reprinted from Nagy and Konya 1998, with permission from Elsevier.)... 

In this chapter the sorption of two organic substances, EDTA and valine amino acid, are discussed. They were selected for two reasons as seen in Figure 2.8, EDTA can be sorbed on the edge sites of montmorillonite. The other reason is the presence of characteristic functional groups in both molecules. The carboxylic and amine groups are very important in organic syntheses and also in humic substances. 

As seen in Section 2.8.2 and in Figure 2.13, some EDTA species are sorbed on the edge site of montmorillonite, stimulating the sorption of cations also. The sorption of EDTA can be studied by 14C-labeled EDTA, and the sorbed quantity can be compared to the different EDTA species present in the solution (Figure 2.15). 

Sakurai and Huang (1995) also found that OX strongly reduced Cu and Cd adsorption on kaolinite and montmorillonite. Recently, Wu et al. (2003) found that Pb adsorbed onto montmorillonite, goethite, and humic acid decreased with increasing concentrations of EDTA and citric acid. 

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