Environmental risk assessment and antimony recovery potential from flotation tailings of the former Sb-As-Cr mine in Lojane, North Macedonia

Legacy flotation tailings from historical mining operations increasingly attract attention as secondary resources for strategic raw materials while simultaneously posing significant environmental risks. The former Sb–As–Cr mine of Lojane in North Macedonia represents one of the largest arsenic(As)- and antimony(Sb)-rich mine waste sites in the region, originating from the processing of hydrothermal vein-type mineralization hosted within the ophiolitic units of the Vadar Zone (Đorđević et al. 2019). Despite the extensive environmental concerns, the potential of these tailings as a resource has remained largely unexplored.

This study aims to assess the feasibility of sustainable recovery of Sb from the Lojane flotation tailings through a detailed mineralogical and geochemical characterization. This will be achieved by using powder X-ray diffraction (PXRD), inductively coupled plasma-optical emission and -mass spectrometry (ICP-OES/MS), and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), alongside evaluating environmentally relevant processes controlling metal(loid) mobility.

Bulk mineralogical analyses reveal a complex assemblage of primary and secondary Sb- and As-bearing phases, including realgar (AsS), pararealgar (AsS), arsenolite (As₂O₃), senarmontite (Sb₂O₃) and cervantite (Sb₂O₄) accompanied by abundant gangue minerals such as quartz (SiO₂) and gypsum (CaSO₄·2 H₂O). This mineralogical diversity reflects the advanced oxidation and weathering processes that have affected the tailings as wells as indicating multiple mineralogical hosts for Sb and As.

Detailed chemical analyses reveal very high concentrations of As (124–480 g/kg) and Sb (12–87 g/kg), and elevated concentration of Fe (7–30 g/kg) as well as traces of Cr (20–190 mg/kg), Ni (90-2.560 mg/kg), Tl (50-205 mg/kg) and Co (10-130 mg/kg).

Electron microscopy investigations provide detailed insights into the micro-scale distribution of Sb- and As-bearing phases as well as their textural relationships with alteration products. The primary As–Sb sulphide assemblage, including relict realgar and stibnite, is pervasively overprinted by chemically heterogeneous cemented crusts containing shrinkage microcracks that form continuous intergranular matrices.

SEM-EDS reveals the presence of two groups of secondary matrices that commonly occur as pore-filling and grain-coating phases. The first group from the Fe-As-Sb-S-O system consists mostly of oxides (arsenolite, stibioclaudetite, hydroxy iron oxides, roméite group As-bearing Sb-oxides), arsenates (scorodite) and sulphates (gypsum). The second group, which is Si–Al–O dominated, consists predominantly of amorphous to poorly crystalline Si–Al oxides with systematically detectable minor contents of As, Sb, Fe and S.

Together, these observations indicate progressive supergene oxidation, element redistribution and the partial immobilisation of As and Sb within secondary phases. This exerts a key control on their environmental mobility and long-term stability.

By linking mineralogical controls, bulk chemistry and leaching behaviour this study provides a comprehensive framework for evaluating both the environmental risks and resource potential of complex As-Sb flotation tailings.

 

Tamara Đorđević acknowledges the financial support of the Austrian Science Fund (FWF) [Grant: P 36828-N].

 

Đorđević, T. et al. (2019): Can. Mineral., 57, 1–21.