Recovery potential of Critical Raw Materials from Sardinian antimony mining wastes: Su Suergiu and Corti Rosas case studies (SE Sardinia, Italy).

The supply of Critical Raw Materials (CRM) is a key priority for the European Union due to its strong dependence on non-EU suppliers. The EU CRMAct (2024) aims to strengthen the domestic supply of CRM within EU, also promoting their recovery from secondary sources such as mining waste, which could become an important resource to reduce the CRM supply risk for EU, which currently produces approximately 600 Mt/y of mine waste, added to the historic stockpile of ~28,000 Mt (NEMO Horizon, 2020). Antimony (Sb) has been classified as a CRM since the first EU list (2011), due to its high supply risk and strong dependence on non-EU production (Kanellopoulos et al., 2024). Given its critical importance and low recycling rate (Dupont et al., 2016), Sb-rich mine waste is now investigated in many old districts of Europe. The study focuses on the abandoned Su Suergiu and Corti Rosas mines in SE Sardinia, the largest in Italy until the 1980s. Su Suergiu hosted a smelter for Sb ore processing into Sb₂O₃ and metallic Sb (Contini et al., 2009), while Corti Rosas operated as a secondary extraction and beneficiation site using gravity, flotation after an initial period of smelting at the site. Between 1901 and 1948, 86,523 t of Sb ore were extracted. Previous studies report that Su Suergiu slags contain Sb-bearing phases such as senarmontite/valentinite (Sb₂O₃), mopungite, and metallic Sb, whereas tailings are dominated by stibnite. Scheelite (CaWO₄) is also commonly present. In contrast, waste rocks and tailings are Sb-depleted and dominated by gangue minerals. The most promising materials from Su Suergiu (slags and tailings) were tested for ore mineral enrichment using hydrodynamic separation techniques (shaking tables) applied to two different particle size fractions. Yellow slags, with an initial grade of 12.9 wt% Sb, produced concentrates containing up to 70 wt% Sb. EPMA analyses showed that Sb mainly occurred as Sb2O3 (valentinite/senarmontite), metallic Sb, and minor Sb-Fe-As alloys. Metal recovery is around 60% for the coarse fraction. In contrast, the glassy slags were characterized by lower Sb contents in both the raw waste (1.5 wt%) and in the concentrates (up to 2.8 wt% Sb), mainly due to Sb entrapment in the silicate glass matrix. Significant amounts of scheelite (up to 4 wt%) were detected, especially in the fine fraction concentrates, with a W recovery of around 43%, suggesting potential for co-recovery. Tailings waste contained 9-10 wt% Sb in the raw material, while shaking table separation produced concentrates up to 28 wt% Sb, mainly as stibnite. Estimated Sb recovery range is around 30-45% for both coarse and fine fraction. Good separation of scheelite (up to 1.7 wt%) was also achieved. These results demonstrate the potential of Sardinian Sb mine wastes as secondary resources for the recovery of Sb and associated CRMs.