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 compo-nent 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 varia-tions 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.
The Maochang bauxite in Guizhou Province is one of the important aluminum ore deposits in southwestern China. Ferruginous spherules, measuring about a few microns across, were found in the transitional layer of the deposit. The EDS and XRD results show that the microspherules are composed mostly of iron (hydr)oxide minerals (goethite) with only weak presence of aluminum and silicon. Occasionally, some pyrite micrograins with dissolved surface are found associated with goethite within the spherules. It is thus suggested that microspherules are linked to pyrite oxidization. It is also thought that microbial activities contribute not only to pyrite oxidization, but also to ball-like assemblage of the iron (hydr)oxides. The mechanism of the formation of ferruginous microspherules is also believed to be important in studying geomicrobiology of bauxite.
In order to investigate the effect of Thiobacillus ferrooxidans on the oxidation of pyrite, two parallel experiments, which employed H2SO4 solutions and acidic solutions inoculated with Thiobacillus ferrooxidans, were designed and carried out at 30℃. The initial pH of the two solutions was adjusted to 2.5 by dropwise addition of concentrated sulphuric acid. The surfaces of pyrite before exposure to leaching solutions and after exposure to the H2SO4 solutions and acidic solutions inoculated with Thiobacillus ferrooxidans were observed by scanning electron microscopy (SEM). There were a variety of erosion patterns by Thiobacillus ferrooxidans on the bio-leached pyrite surfaces. A conclusion can be drawn that the oxidation of pyrite might have been caused by erosion of the surfaces. Attachment of the bacteria to pyrite surfaces resulted in erosion pits, leading to the oxidation of pyrite. It is possible that the direct mechanism plays the most important role in the oxidation of pyrite. The changes in iron ion concentrations of both the experimental solutions with time suggest that Thiobacillus ferrooxidans can enhance greatly the oxidation of pyrite.
LU Jianjun LU Xiancai WANG Rucheng LI Juan ZHU Changjian GAO Jianfeng
