Metal Speciation in Surface Waters of the Great Lakes Region

摘要

Predicting the dynamics of trace metals such as uranium by thermodynamic prediction models is contingent upon accurate stability constants. Conditional stability constants (K') for the binding of uranyl ion UO2(+2) to humic substances were determined by both Scatchard analyses and by fitting the data to a Gaussian model of multiple sites. UO2(+2) was separated from that which was bound to humic material by ion exchange. Uranium concentration was measured by laser fluorometry. There is a broad range of strengths of sites such that K' was dependent on the UO2(+2)/humic ratio. The maximum binding capacity of the humic material was .000483 M/g. The log K' determined for log metal/ligand ratios of -1.5 to -0.5, the ecologically significant range of interest for UO2(+2), which was from 10 - 50 microgram/l at the carbon concentration of 2.36 mg/l used in this study, was determined by Scatchard analysis to be 7.38. The estimate based on a Gaussian distribution was 6.85.