Hydrated transition metal ions adsorption

Figure 2.3. Surface complexation phenomena in the retention or desorption of metals from mineral surfaces. Nonspecific (exchangeable) adsorption consists of electrostatic bonds only and the ions retain their hydration sphere (outer-sphere complexes) specific (nonexchangeable) adsorption requires removal of the hydration sphere (inner-sphere complexes). Alkali and alkaline earth metals tend to form outer-sphere complexes, hence their tendency to be loosely bound and readily exchangeable with other ions in solution. Transition metals tend to form inner-sphere complexes, which are more strongly bound and less exchangeable (Cotter-Howells and Paterson, 2000). Representation of (a) an outer-sphere complex, (b) an inner-sphere complex, and (c) a solution complex (see also Figure 2.2). The solid substrate is textured with the solution above this. Unlabeled spheres represent oxygen atoms, and the spheres labeled M represent metals in the substrate or in solution. Smaller shaded spheres labeled H are hydrogen atoms. (Adapted from Brown et al., 1999 Cotter-Howells and Paterson, 2000.)...

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