Wednesday, November 7, 2007 - 1:15 PM
326-12
Influence of DOC on Cd, Cr, Cu, and Ni Retention by Soil Solid Phases.
The retention of Cd, Cr, Cu, and Ni by iron oxides, organic matter, and silicate clays is studied over 8 months using a batch reactor with compartments. This reactor attempts to emulate a natural soil where different solid phases compete for the retention of a variety of metals through a common solution. Studying the competition among different soil solids towards metal retention is important to understand which solid phase(s) could potentially limit metal solubility and bio-availability. Analogously, competition among different metals is important since in natural soil environments various metals are likely to be contained in an individual waste. The metals studied are classified from hard to soft according to the Pearson Hardeness concept which explains metal complexation according to the chemical nature of ligands and metal properties. Metal speciation in solution (free, DPASV-labile, and total dissolved Cu) and in individual solid phases (exchangeable and total Cu) is determined. In addition, DOC and total organic carbon on the mineral phases are monitored over time. Our results suggest total dissolved metals are controlled by DOC while metal speciation in solution and their tendency to react with a particular solid seem highly influenced by metal properties. For example, the rate of sorption of Cd and Cu decreases as DOC increases. Besides, the concentration of total dissolved Cd and Cu show a linear relationship with DOC. However, Cd exists mostly as labile species while Cu exists mainly as non-labile Cu-DOC complexes. In addition, ~ 90 % of the total Cd sorbed on organic matter occupies exchangeable positions while ~ 96 % of the total Cu sorbed on organic matter occurs as non-exchangeable species. Data on the speciation of Cd, Cr, Cu, and Ni in both the solution and the solid phases will be presented together with a comprehensive analysis of all the data collected.
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