Evaluating CRM potential and environmental impact of Sardinian mining and metallurgical waste: the case of Su Suergiu and Corti Rosas antimony mines (SE Sardinia)

Sb-bearing wastes from Su Suergiu and Corti Rosas mines (Sardinia) were characterized through integrated mineralogical, geochemical and leaching analyses to evaluate both resource recovery potential and environmental risk. Su Suergiu wastes were recognized both as the most promising materials for Sb recovery (smelting slags) and as the most polluting, with significant release of Potentially Toxic Elements (PTEs) into the local streams down to the Flumendosa, the main River of the region. The domestic supply of Critical and Strategic Raw Materials (CRM, SRM) is a strategic priority for the European Union, mainly due to its dependence on non-EU suppliers. The aim of the EU Critical Raw Materials Act (2024) is to promote the domestic supply of CRM and SRM, also diversifying the import supply chains (EC, 2024). In this framework, CRM and SRM retrieved from mining wastes could become a major resource to reduce this dependence. In EU, approximately 600 Mt/y of mining waste, annually added to the historic stockpile (28,000 Mt), are produced by sulphide mines, thus representing the largest volume of Extractive Waste (NEMO Horizon, 2020). Antimony (Sb) is classified as a CRM with high supply risk due to its strong import dependence and concentration of primary production outside the EU (e.g. Kanellopoulos et al., 2024). The global demand for Sb is increasing due to its strategic applications, whereas only ~20% of the total supply currently derives from recycling, mainly from industrial residues and end-of-life products (Dupont et al., 2016). Given its critical importance and limited substitution options, alternative secondary sources, such as Sb-rich mining waste, are being investigated. The Gerrei district, in SE Sardinia, represents one of the most important areas for mining extraction in the region, with several ore deposits exploited for around 100 years. Among these, the Su Suergiu (Villasalto) and Corti Rosas (Ballao) deposits, which belong to an Sb-W-As-Au hydrothermal mineral system hosted within low-grade metamorphic rocks of the Sardinia Variscan basement, represent the main antimony district in Italy (Funedda et al., 2018). Sb mineralization occurs as stibnite (Sb₂S₃) and scheelite (CaWO4)- bearing lenses, associated with arsenopyrite, pyrite and minor Zn-Pb-Cu sulphides hosted in a quartz-calcite gangue. From 1882 to 1980, Su Suergiu hosted Sardinia first antimony smelting plant, which was the largest industrial complex in Italy for antimony ore extraction and metallurgy. Between 1900 and 1969, the smelter produced both Sb2O3 (~5,000 t) and metallic Sb (~13,000 t), using local ores, replaced by imported concentrates in the late stages of activity (Contini et al., 2009). The Corti Rosas mine was exploited from the late XIX century until 1970. It operated as a parallel site to Su Suergiu, extracting and pre-concentrating antimony minerals, initially in small furnaces then using gravity and flotation, before sending the rich concentrates to the Su Suergiu smelter for final Sb production. Overall, between 1901 and 1948, a total of 86,523 tonnes of Sb ore were extracted from the two mines. Today, substantial wastes are still present in the two sites, which have neither undergone remediation nor been evaluated for secondary metal recovery. Su Suergiu mine includes smelting slags (~66,000 m³), waste rocks (~146,000 m³) and jig tailings, while flotation tailings and slags are present at Corti Rosas (Fancello et al., 2023). This study showed that mine wastes at Su Suergiu are variably enriched in Sb, reaching up to 9.7 wt.% in Na-rich slags, where Sb is hosted in phases such as mopungite, valentinite, senarmontite and minor metallic Sb. Together with antimony, Zn is enriched too, up to 4.47 wt.%, while Waste rocks are more gangue- 2 - IAGOD 2026 extended abstract volume dominated, with Sb contents of 1-2 wt.%. Jig tailings still contain significant Sb (up to 6.9 wt.%), together with high S content (~5 wt.%), mainly as stibnite and Fe-Sb-O phases. At Corti Rosas, wastes are generally poor in Sb (0.35-1 wt.%). Based on these data, the most promising materials for recovery were selected (Su Suergiu slags and jig tailings) and were first treated on shaking tables to separate Sb-phases from the gangue. The preliminary results yielded concentrates with approximately 20% mass recovery. The yellow slags concentrates are enriched in metallic Sb, with minor oxides and hydroxides, along with magnetite; glassy slags showed the lowest Sb recovery but interesting contents of scheelite (W, also a CRM). Jig tailings were already enriched in Sb sulphide (stibnite) as a result of historical gravity processing, and our treatment on shaking table enhanced the stibnite concentration and removed most of the silicate gangue (quartz, gypsum, muscovite) . Our preliminary analyses showed that the Na-rich slags are the main environmental hazard at Su Suergiu, generating alkaline leachates (pH up to 11.2), which promote high mobilization of Sb (up to 128 mg/L), followed by neutral-pH waste rocks, which also contribute to Sb release (up to 13.6 mg/L). Interestingly, the jig tailing sample at Su Suergiu was the only one producing acid drainage (pH 3.8). Despite the lower pH, this still promotes Sb release (up to 0.88 mg/L) and enhances the mobility of other PTEs (Zn, Cu, Cd, Ni and Pb). At Corti Rosas, smelting slags also produced alkaline leachates with substantial Sb release (up to 16.73 mg/L). However, the main environmental hazard is represented by flotation tailings, which, despite releasing lower Sb (96.22 µg/L) and As (3.95 µg/L), have finer grain sizes which enhance PTEs dispersion into the Ballao valley down to the Flumendosa, which already receives the contamination from Su Suergiu mine. Our results showed that the slag samples (Su Suergiu) are the most polluting waste, with tailings (from the two mines) being the second, while contribution from waste rocks is negligible. The recovery of metals from these residues and consequent correct managing of secondary tailings could contribute not only to mitigate antimony supply risk for EU but also to strongly reduce the environmental impact of the mining and smelting sites.