Sn-hosted iron borates, specifically vonsenite and hulsite, represent an underexplored critical mineral resource. Unlike cassiterite, for which extraction methods are well-established, there are no effective strategies for recovering tin from these complex lattice structures. This study presents an investigation into the extractability of tin, boron, and iron from a skarn deposit in Western Tasmania.
Mineralogical characterisation identified that tin is structurally incorporated within the iron-borate lattice rather than existing as discrete oxide phases. Two processing pathways were evaluated to overcome this refractory nature: oxidative roasting and direct acid leaching. Oxidative roasting with sodium carbonate successfully solubilised boron but failed to liberate tin, likely due to the formation of insoluble iron-tin phases during thermal treatment.
Direct leaching investigations revealed that traditional mineral acids were ineffective at breaking down the tin-bearing lattice. However, the introduction of oxalic acid into the mineral acid resulted in a sharp increase in tin recovery from less than 40% to 89%. The study discusses the chemical behaviour of this mixed-acid system, including the inferred role of the oxalic acid additive in improving tin solubility. Unfortunately, iron is also highly soluble under these conditions, complicating the chemistry of selective tin recovery from the leach solution.