Moderately charged sphere

As with the moderately charged cylinder, an approximate potential profile for a moderately charged sphere in the presence of a mixed electrolyte can be found by using the effective-valence planar solution of Eq. [69] in either the asymptotic approximation of Eq. [147] or the NLDH approximation of Eq. [177]. Eor the latter we need the DH solution to Eq. [165] for d = 3 subject to boundary conditions [160]. The result is given by Eq. [307] and provides... 

Like calcium, strontium has moderate mobility in soils and sediments, and sorbs moderately to metal oxides and clays (Hayes and Traina 1998). The Sr2- ion is strongly hydrated and is firmly coordinated with six or more water molecules in aqueous solution. When Sr2- ions sorb on negatively charged mineral surface sites, the hydration sphere is retained (O Day et al. 2000). Strontium sorbs as hydrated ions on the surface of clay minerals (kaolinite), weathered minerals (amorphous silica), and iron oxides (Sahai et al. 2000). Sorbed carbonate on iron oxides enhances the sorption of Sr2- and permits the nucleation of Sr2- as strontium carbonate (Sahai et al. 2000). On calcite (calcium carbonate), Sr2 sorption occurs by electrostatic attraction as hydrated ions. However, at higher concentrations, precipitation of strontianite (strontium carbonate) occurs and strontium is likely to be less mobile (Parkman et al. 1998). 

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