Characteristics of manganese‐calcium exchange behavior on kaolinite and illite and pH influence

Water emanating from coal‐mine sites must be impounded and treated in a sediment pond to lower suspended solids, manganese (Mn) and other heavy metal ion concentration before release. Suspended solids in sediment ponds in Kentucky and many Eastern U.S. coal mines sites generally contain mostly kaolinite and illite. A Mn‐Ca exchange equilibrium approach was used to evaluate Mn2+ adsorption onto kaolinite and illite clays. Prior to Mn2+ equilibrium experiments, the clays were adjusted to three different pH levels, (pH 5.2, 6.8–6.9 and 8.7). It was observed that both kaolinite and illite clays exhibited two surface exchange sites for Mn2+. However, the occurrence of the two surface exchange sites on kaolinite was influenced by treatment pH whereas that on illite was not. At a given pH level, Mn2+ selectivity by illite clay mineral was much greater than that by kaolinite. Practical implications of these findings in treating sediments are discussed.