Centre for Mined Land Rehabilitation, Sustainable Minerals Institute, The University of Queensland, Brisbane, Queensland, 4072, Australia.
School of Chemical Engineering, The University of Queensland, Brisbane, Queensland, 4072, Australia.
Environ Pollut. 2018 Nov;242(Pt B):1500-1509. doi: 10.1016/j.envpol.2018.08.027. Epub 2018 Aug 17.
A massive and dense textured layer (ca. 35-50 cm thick) of hardpan was uncovered at the top layer, which capped the unweathered sulfidic Cu-Pb-Zn tailings in depth and physically supported gravelly soil root zones sustaining native vegetation for more than a decade. For the purpose of understanding functional roles of the hardpan layer in the cover profile, the present study has characterized the microstructures of the hardpan profile at different depth compared with the tailings underneath the hardpans. A suit of microspectroscopic technologies was deployed to examine the hardpan samples, including field emission-scanning electron microscopy coupled with energy dispersive spectroscopy (FE-SEM-EDS), X-ray diffraction (XRD) and synchrotron-based X-ray absorption fine structure spectroscopy (XAFS). The XRD and Fe K-edge XAFS analysis revealed that pyrite in the tailings had been largely oxidised, while goethite and ferrihydrite had extensively accumulated in the hardpan. The percentage of Fe-phyllosilicates (e.g., biotite and illite) decreased within the hardpan profile compared to the unweathered tailings beneath the hardpan. The FE-SEM-EDS analysis showed that the fine-grained Ca-sulfate (possibly gypsum) evaporites appeared as platelet-shaped that deposited around pyrite, dolomite, and crystalline gypsum particles, while Fe-Si gels exhibited a needle-like texture that aggregated minerals together and produced contiguous coating on pyrite surfaces. These microstructural findings suggest that the weathering of pyrite and Fe-phyllosilicates coupled with dolomite dissolution may have contributed to the formation of Ca-sulfate/gypsum evaporites and Fe-Si gels. These findings have among the first to uncover the microstructure of hardpan formed at the top layer of sulfidic Cu-Pb-Zn tailings, which physically capped the unweathered tailings in depth and supported root zones and native vegetation under semi-arid climatic conditions.
在顶部发现了一层厚达 35-50 厘米的坚硬、致密纹理层（硬磐），覆盖在未风化的硫化铜-铅-锌尾矿层之上，为支撑砾质土壤根系区和维持原生植被提供了物理支撑，这些植被已经存在了十多年。为了了解硬磐层在覆盖层剖面中的功能作用，本研究对硬磐剖面不同深度的微观结构进行了特征描述，与硬磐下的尾矿进行了对比。采用了一系列微光谱技术来研究硬磐样品，包括场发射扫描电子显微镜结合能量色散光谱（FE-SEM-EDS）、X 射线衍射（XRD）和基于同步加速器的 X 射线吸收精细结构光谱（XAFS）。XRD 和 Fe K 边 XAFS 分析表明，尾矿中的黄铁矿已被大量氧化，而针铁矿和水铁矿则在硬磐中大量积累。与硬磐下未风化的尾矿相比，硬磐剖面中 Fe 层状硅酸盐（如黑云母和伊利石）的含量减少。FE-SEM-EDS 分析表明，细小的 Ca 硫酸盐（可能是石膏）蒸发盐呈板状沉积在黄铁矿、白云石和结晶石膏颗粒周围，而 Fe-Si 凝胶则呈现出针状纹理，将矿物聚集在一起，并在黄铁矿表面形成连续的涂层。这些微观结构的发现表明，黄铁矿和 Fe 层状硅酸盐的风化以及白云石的溶解可能促成了 Ca 硫酸盐/石膏蒸发盐和 Fe-Si 凝胶的形成。这些发现首次揭示了在硫化铜-铅-锌尾矿顶层形成的硬磐的微观结构，它在深度上覆盖了未风化的尾矿，并在半干旱气候条件下为根区和原生植被提供了支撑。
