The reactive uptake and release of Mn(ll), Co(ll), Ni(ll), and Zn(ll) by sediments from a mining-contaminated stream, Pinal Creek, Arizona

Abstract

It was hypothesized that the transport of Co, Ni, and Zn in Pinal C~eek, Arizona, is controlled primarily by interaction with continuously forming Mn-oxide coatings on sediments in the hyporheic zone. Column experiments were used to investigated the effects of Mn-oxide content and microbial Mn-oxidation on the uptake and release of Mn, Co, Ni, and Zn at pH 7. Column influent composition, dissolved oxygen, pH, and retention time were designed to simulate natural conditions in the hyporheic zone at Pinal Creek. Microbial oxidation increased Mn retention between 5% and 410 %, increasing as Mn-oxide sediment content decreased. Co uptake resulted in the surface oxidation of Co(II) to Co(III). A mechanism of continuous removal controlled Co uptake, possibly Co (hydr)oxide precipitation or exchange of Co with structural Mn. Only a small amount of Co uptake was reversible. Ni uptake occurred as equilibrium adsorption. Ni uptake was completely reversible in the presence of dissolved Mn. Desorption was kinetically limited, suggesting changes in the Mn-oxide surfaces over the duration of column experiments. Zn uptake was controlled by a mechanism of continuous removal, possibly hausmannite-hetaerolite solid solution formation or interaction with carbonates. Zn uptake was largely irreversible.