Clay minerals, metal oxyhydroxides, and carbonates are important earth surface materials, which are secondary minerals formed from primary minerals with water and atmosphere under earth surface conditions. These minerals usually possess a high surface area and are highly reactive to foreign dissolved species; therefore, they play important roles as sorbents for trace elements in natural water. Predicting distributions of trace elements between solution and mineral phases is important for understanding migration and accumulation behaviors of toxic and useful elements on the earth surface. To predict distributions, it is required to elucidate the chemical processes governing the sorption of trace elements on or in minerals, and to model chemical processes quantitatively. The important chemical processes governing the sorption of trace elements by earth surface materials are adsorption, surface precipitation, ion exchange, mineralization, and coprecipitation. The current understanding of these chemical processes as revealed from laboratory experiments is reviewed, as well as current approaches to modeling.
