Systematic characterization of historical tailings for possible remediation and recovery of critical metals and minerals – The Yxsjöberg case

Abstract As the need to address environmental concerns in mining and the demand for critical metals and minerals increase, historical tailings are among the mining waste repositories being sought after. However, there is only limited information available about such repositories, and hence there is a need to fill these knowledge gaps. In this paper, a conceptual framework is proposed for how relevant information about historical tailings can be generated and structured in a systematic manner. The case of the closed Yxsjoberg mine in Sweden is used to demonstrate how this framework is being used. A site-specific sampling strategy and technique was identified, and based on the observed lithology, tailings particles were studied to understand their distribution across the repository. Using Mineral Liberation Analysis (MLA), the modal mineralogy, mineral associations, and mineral liberation by particle size of the tailings were determined. The Smaltjarnen tailings repository of Yxsjoberg has potential for critical metals and minerals, including tungsten (W) and fluorite (CaF2) but also contains minerals of environmental concern as pyrrhotite and pyrite. It has on average 0.15% WO3 concentration in the sampled locations, indicating approximately 3300 tons of WO3 in the repository. Scheelite mineral grains are mostly (>50 wt%) locked in tailings particles that have a number of mineral grains (binary, ternary or even more complex) in the dominating particle size fraction −600 to +149 μm. Mineral locking is mostly with calcium-bearing minerals ilvaite, fluorite and garnet-gross-andradite. Pyrrhotite has been the most reactive acid-generating mineral, and hence is more depleted than pyrite in the weathered locations. The heterogeneity of tailings across the repository suggests a possible existence of geometallurgical domains that require further assessment to evaluate their metallurgical performance. The obtained information and knowledge about these tailings will hereinafter be used to develop sustainable processes for remediation and recovery of the critical metals and minerals.