Reaction Among Humic Substances, Clays, and Metals

2 Reaction Among Humic Substances, Clays, and Metals 

Commonly, the amount of metal ions adsorbed by the solid surface increases with increasing pH for humic substances, clays, or clay—humic acid mixtures. Metal-ions adsorbed in acid media increase with pH until the threshold value required for partial dissolution of solid and formation of soluble metal-humate complexes is exceeded (Fig. 3.18). Metal-organic complexes experience three types of interactions, which 

Protons (H+) compete with cations for organic binding sites 

Hydroxyl ion (OH-) competes with humic substances for the cationic metal-ion 

Soft metals compete with hard metals for organic functional groups 

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