Mineral Formation in Soils of Mountain Ecosystems of the North Caucasus Exposed to Mining Waste

The long-term operation of the Sadon lead–zinc plant (North Caucasus, Russia) has led to the formation of technogenic anomalies of chemical contamination, causing toxicity in soils and adjacent environmental media. For the first time, a combination of synchrotron-based X-ray absorption fine structure spectroscopy (XAFS) and X-ray diffraction (XRD) was applied to diagnose authigenic metal-containing mineral phases in an industrially contaminated soil sample from the mountainous areas of the North Caucasus. A comparative assessment of the carrier phases of Cd, Pb, Cu, Zn, Ni, Mn, Cr, and Ti was performed using sequential extraction. Phases of metal compounds with sulfur and metal oxides have been identified in technogenically transformed soil (Technosol). Analysis of the near-edge spectral region (XANES) provided insights into the valence state and coordination environment of the absorbing atoms, while analysis of the extended spectral region (EXAFS) elucidated the characteristics of the local atomic environment. XAFS and XRD data consistently identified ZnS, MnO2, Cr2O3, and PbCO3 mineral phases, confirming their crystal structure and metal coordination environments. These findings were further supported by SEM-EDX detection of Zn, Cu, and Pb. Fractionation analysis revealed that Cd, Zn, and Ni shifted toward more mobile forms under contamination, whereas Mn and Cr maintained background binding patterns, emphasizing their differential ecological stability.