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Solubilization of manganese dioxide-bound copper by naturally occurring organic compounds.

Sorption of metals onto manganese oxides is an important mechanism for retarding migration in soils and sediments. Subsequent influx of natural organic compounds can bring about metal release, thereby increasing metal mobility and bioavailability. This paper examines the release of Cu from a synthetic MnO[sub 2] phase. When natural organic compounds possessing only reductant characteristics (e.g., hydroquinone and pyruvate) are introduced, Cu release is linked to the progress of the MnO[sub 2] reductive dissolution reaction: Mn[sup II] generated in the reduction step competes effectively with Cu for a diminishing number of sorption sites. Organic compounds capable of forming stable Cu complexes in solution (e.g., oxalate and citrate) cause additional Cu release that can surpass release by reduction processes alone. Additional experiments are described in which the reductant and complexant properties of natural organic matter samples are evaluated as they pertain to the release of MnO[sub 2]-bound Cu. 61 refs., 8 figs.