Coagulation specifically adsorbable species

Simple multivalent cations such as Mg2+ and Al + are ineffective in charge reversal for coagulation (62) experiments and in activation for froth flotation (35). The related positive hydroxo complexes do function as coagulants and flotation activators and hence must be specifically adsorbed. By knowing the appropriate hydrolysis constants and the most effective species (in flotation systems apparently M+z(OH)Vi and in coagulation, polynuclear complexes), one can predict the pH range in which each cation can be expected to adsorb strongly. 

Recent studies indicate that the adsorption of metal ions is controlled only in part by the concentration of the free (aquo) metal ion of considerable importance is the ability of hydroxo and other complex ions and molecules to adsorb. There have been two apparently divergent approaches to describe the role played by hydroxo metal complexes in adsorption at solid-aqueous electrolyte interfaces. Matijevic et al. (9) have proposed that specific hydrolysis products—e.g., Al8(OH)2o4+ in the A1(III)-H20 system, are responsible for extensive coagulation and charge reversal of hydrophobic colloids. It has also been demonstrated by Matijevic that the free (aquo) species of transition and other metal ions... 

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