Agglomeration and Ripening

This discussion should indicate that selection of an equilibrium constant for a precipitating solution is extremely difficult. Equilibrium constants 

According to Walton, dissolution is nearly always controlled by the rate of diffusion of the species away from the solids. Accordingly, the rate law. 

At the outset of any discussion on heterogeneous equilibria it is important to realize that heterogeneous equilibrium calculations only apply when there is an excess of the solid of interest present. If solid is absent, the equilibrium calculations are not valid for predicting solution composition they may only be used to test whether saturation with a particular solid exists. 

A solid phase or precipitate in a water containing no other constituents than those derived from the dissolution of the precipitate. The solutes produced by the dissolution of the precipitate do not react (form complexes, hydrolyze, etc.) in solution at moderate concentrations and at an approximately neutral pH. Very few examples of this situation exist in water chemistry. Solids such as CaFz(s) and BaSO fs) generally fit into this category under natural water conditions. 

Precipitates that dissolve to produce reactive solutes. The reaction may be hydrolysis (protolysis), or complex formation. Examples are CaC03(s) and Al(OH)3 gj dissolving in water. 

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