Chemical speciation of Cd,Cu, Pb,and Zn in mixed freshwater,seawater, and brine solutions |
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| Authors: | David T Long Ernest E Angino |
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| Institution: | Department of Geology, University of Kansas, Lawrence, KS 66045, U.S.A. |
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| Abstract: | A theoretical model was developed to study the chemical speciation of the trace elements Zn, Cd, Cu and Pb aqueous solutions and their responses to variations in ionic strength and complexation. Two mixing solutions were investigated, a freshwater-seawater system and a freshwater-brine system. The brine was a calcium, sodium-chloride solution with a molal ionic strength of two. Trace element associations with the ligands OH?, Cl?, CO2?3, SO2?4, and HCO?3 were considered at pHs from 3.5 to 11.0 at 25°C. In general, the relative importance of the various ligand-trace element complexes can be predicted from a comparison of their stability constants. However, the effect of pH on the importance of a given complex is not readily apparent from the stability constants. Freshwater-seawater mixtures, as might be found in a totally mixed estuary, show that seawater composition is the dominant control on chemical complexing. Chloride complexing is similar for lead and zinc in the freshwater-brine mixtures. This similarity may account in part for the association of lead and zinc in strata-bound ore deposits. |
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