Colloids may be solvated (lyophilic) or non solvated (lyophobic). Clays belongs to lyophilic group. Electric charge on clay particles is one of the causes of the stability of suspensions, solvation is another. Because of the heterogeneous nature of salt substances with high di-electric constants must be charged positively in relation to those with lower di-electric constants. Since water has a high di-electric constant particles suspended in it are mostly negatively charged. Hydro salts of SiO2 and clay are negatively charged, those of Fe(OH)3 and Al(OH)3 positively.

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