Interfacial reactions and the fate of heavy metals in soil water systems

The fate of heavy metals in soil water systems is primarily controlled by the congruent incongruent solubility of the carbonates, oxides, sulfates, and sulfides of metals and by the adsorptions of free and complexed metals at solids solution interface. The presence of organic substances modifies the overall interfacial reactions. Adsorption of copper, zinc, lead, and cadmium increased abruptly at a given pH when the free metal ionic species dominates the system. At low pH, lead and cadmium were negatively adsorbed, which results in an excess of lead and cadmium ions in the bulk solution phase. Copper and zinc were always adsorbed by all four solids (SiO₂, γ-Al₂O₃, Evesboro, and Metapeak) investigated. In a neutral to acidic environment, the adsorption reaction appears to be the most important process in controlling the chemical make up of the soil water system.