ABSTRACT
The surface-exchange reactions postulated for metal cations and anions on calcite and, are consistent with many experimental observations made using calcite and other salt-type solid phases. The use of surface-exchange reactions to successfully describe the sorption of cations and anions on calcite does not presuppose a specific molecular nature of the surface complexes. Natural soils and aquifer materials are composed of a mixture of mineral and organic material spanning the clay, silt, sand, and gravel size range. Cadmium was used for the test calculation because a consistent set of constants was available for its surface exchange on all three sorbents from high Ca electrolyte solutions where the competitive effects of Ca had been explicitly addressed. The multisorbent model calculation underscores the need for accurate site concentration measurements of different sorbents in a aquifer material to understand and predict metal ion sorption.
