Highly Zn, Mn-rich calcite in calcareous tufa from the Qixiashan Pb-Zn Mine, Nanjing: a possible candidate for Zn-Mn removal from mining impacted waters

Abstract

The exploitation of metallic mines may cause serious environmental problems. The removal of the heavy metals from the contaminated
mining environments has become an urgent issue. In this paper, the occurrence and distribution of heavy metals in the calcareous
tufa collected from the mining laneway of the Qixiashan Pb-Zn Mine in Nanjing were investigated by using multiple mineralogical
techniques. Examination by X-ray diffraction spectrum (XRD) shows that calcite is the major component of the calcareous tufa.
Several heavy metals such as Mn, Zn, Mg, Fe and Pb are detected in calcite by means of electron microprobe analysis. Although
the heavy metal contents in the hostrock and the formation water are significantly low, the contents of Mn, Zn, Mg, Fe and
Pb in the tufa calcite are as high as 23.65 wt%, 9.6 wt%, 0.76 wt%, 4.44 wt% and 0.66 wt%, respectively. The back-scattered
electron image shows complex compositional zoning texture in the tufa, which is linked directly to variations in heavy metals,
particularly in Mn and Zn. In addition, we also observed floccule and helical precipitations, which may be derived from the
metabolism of the microbe. It is deduced that the occurrence and high concentration of heavy metals in tufa may be controlled
by the activities of microbes. The results presented in this work suggest that calcite will be an important candidate for
the remediation of the heavy metal contamination in mining areas.