Cobalt-calcium ion exchange

FIGURE 2.2 The equilibrium distribution of cobalt ions as a function of equilibrium cobalt ion concentration for cobalt-calcium ion exchange at a constant pH value. T = 33°C pH 6.5. (Reprinted from Nagy et al. 1997, with permission from Elsevier.)... 

Under these experimental conditions, the equilibrium constant of cobalt-calcium ion exchange in montmorillonite cannot precisely be determined for two reasons. First, for the determination of the equilibrium constant, the integration has to be in the whole range of X. It is seen in Figure 2.8 (and it is in good agreement with the data in Table 2.7) that there is a surface concentration range (XCa = 0.8-1... 

The results of the cobalt and calcium ion exchange on montmorillonite shows that the ion-exchange isotherm equation (Chapter 1, Equation 1.94) can be applied well in this case, the estimated isotherm parameters (t, and K/K have real physical meaning and their values can be confirmed by independent experimental procedures. 

A metal-nucleotide complex that exhibits low rates of ligand exchange as a result of substituting higher oxidation state metal ions with ionic radii nearly equal to the naturally bound metal ion. Such compounds can be prepared with chromium(III), cobalt(III), and rhodi-um(III) in place of magnesium or calcium ion. Because these exchange-inert complexes can be resolved into their various optically active isomers, they have proven to be powerful mechanistic probes, particularly for kinases, NTPases, and nucleotidyl transferases. In the case of Cr(III) coordination complexes with the two phosphates of ATP or ADP, the second phosphate becomes chiral, and the screw sense must be specified to describe the three-dimensional configuration of atoms. 

By this method, the ion-exchange isotherms and selectivity coefficients can precisely be determined in a wide surface concentration range, which allows the construction of the ion-exchange isotherm and selectivity function, and the integration of the selectivity function (Chapter 1, Section 1.3.4.2.1, Equation 1.81). An example of a cation-exchange isotherm and isotherm parameters is shown in Figure 2.2 for the cation exchange of cobalt ions and calcium-montmorillonite. 

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. 

Hair is an excellent ion exchange system. Metallic ions may be sorbed to hair in multiple forms such as lipids (e.g., calcium stearate) or as particulates (e.g., metal oxides). Many metallic ions such as copper (-1-2) [11] can adsorb to hair, especially after frequent exposure to swimming pool water. It has been suggested that metallic ions such as chromium, nickel, and cobalt may bind to hair from swimming pool water [11]. Sorption of metallic ions like calcium or magnesium occurs even from low concentrations in the water supply rather than from hair products. However, fatty acids present in hair products enhance the adsorption of most of these metallic ions to the hair surface, as described earlier. Heavy metals such as lead and cadmium have been shown to collect in hair from air pollution [12], and other metals like zinc are available from antidandruff products, from the zinc pyrithione active ingredient. 

Potassium, sodium, calcium and other positively charged ions present in the channel are exchangeable and get replaced by heavy metal ions. Heavy metals present in wastewater (chromium, mercury, lead and cadmium) are effectively adsorbed on zeolites. Clinoptilolite is a widely used zeolite for wastewater treatment due to its higher selectivity and ion exchange capability to remove heavy metal ions including strontium and cesium (Grant et al. 1987). Vaca Mier et al. (2001) studied the selectivity of zeolite for the removal of various heavy metals and observed that zeolites show higher selectivity for lead ions followed by cadmium, copper and cobalt. Table 2.2 (Bailey et al. 1999) shows the some of the reported adsorption capacities of zeolites. 

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