ESTIMATION OF THE CONCENTRATIONS OF TRACE-METALS IN NATURAL SYSTEMS -THE APPLICATION OF CODISSOLUTION AND COPRECIPITATION APPROACHES TO ELBERROCAL (SPAIN) AND POCOS DE CALDAS (BRAZIL)

Trace element concentrations in natural systems indicate that, in most cases, solubility controls are not exerted by pure solid phases. The cycling of trace metals in the environment is coupled to the chemistry of the major components. To model this behaviour we have developed a methodology based on codissolution and coprecipitation approaches. We have applied this methodology to the El Berrocal (Spain) and Pocos de Caldas (Brazil) sites. Trace metals under investigation were: Ba, Cu, Mn, Ni, Sr, and U. The models took into account: (1) the observed asso ciation of copper and uranium with iron oxyhydroxides (both in El Berr ocal and in Pocos de Caldas), (2) the interaction of barium and mangan ese with calcite in El Berrocal, and (3) the association between stron tium and fluorite in Pocos de Caldas. In most cases, the results were in good agreement with field data, showing that application of these a pproaches can reproduce more accurately the measured concentration of trace metals in groundwater than the assumption of a pure solid phase controlling the concentration of trace metals in solution, However, so me problems still remain, such as the description of nickel concentrat ions in groundwater. (C) 1998 Elsevier Science B.V. All rights reserve d.