Metal retention by iron oxide precipitation from acidic ground water in Dalarna, Sweden

This study provides a characterization of goethite and lepidocrocite precipitates that form from ground water contaminated by acid mine leachate in Dalarna, Sweden. Chemical extraction techniques and electron microprobe analyses indicate that Al, Cu, Ni, S, Si, Ti, and Zn may be retained in the goethite structure. The metals are retained by either isomorphic substitution for Fe in goethite or by adsorption to the oxide surfaces, and it is most likely that the nonmetals S and Si occur as adsorbed SO42− and silica (SiO2) inclusions. Among the metals, Al has the greatest retention by goethite, at levels up to 5.5 mole %. The unit cell dimensions for goethite are determined from the XRD patterns, which indicate that there is a contraction in the unit cell volume. This reduction in cell volume can reasonably be attributed to the Al-for-Fe substitution in goethite. The results presented here suggest that the retention of Cu, Ni, Ti, and Zn by Fe oxides is not a significant sink for these heavy metals in this study.