• ' ' '

Calculations of stability constants of surface complexes always involve some assumptions which may be disputable. Therefore, demonstration of correlation of pH 50 obtained for different heavy metal cations of the same valence and their hydrolysis constants would be more convincing. Fig. 19 shows the Schindler's data and results from more recent publications [24,29]. The data from Ref. 24 show some degree of linear correlation between pH 50 and the first hydrolysis constant, but the data from Ref. 49 are not correlated. Ref. 68 shows a somewhat idealized picture, while in fact the correlation between the hydrolysis in solution and sorption on silica is moderate.