Investigation of zinc uptake processes by manganese-oxide-coated sediments from a mining-contaminated stream, Pinal Creek, Arizona

Abstract

In a mining-contaminated stream, Pinal Creek, AZ, Mn-oxide-coated streambed sediments help to attenuate dissolved Zn, Ni, and Co in the stream. Recent laboratory studies have found that Zn uptake occurs continuously and irreversibly in Pinal Creek sediments. In this study, Zn uptake processes were investigated by conducting column and batch experiments with varying pH, water composition, and solid types. Zn uptake was found to be dependent on pH, different phases of pre-existing Mn oxides, and the presence of dissolved Mn, and was independent of the dissolved carbonate concentration. Formations of Zn hydroxide and hetaerolite-like phase are consistent with many of the observations. Zn uptake was especially influenced by different structures of pre-existing Mn oxides in the absence of dissolved Mn. The formation of hetaerolite (ZnMn204) was identified by EXAFS spectroscopy in stream-incubated Mn oxides reacted with Zn in a laboratory column.