Abstract
Comprehensive mineralogical and technological investigations of tin-bearing weathering crusts from the Syrymbet deposit (Northern Kazakhstan), characterized by low tin grades and a high degree of mineral dispersion, are presented. The particle-size distribution, mineralogical composition, chemical composition, and the distribution of tin among size fractions and processing products were studied. The results show that the majority of tin is associated with the fine-grained clay fraction, which contains up to 70%–74% of the total metal inventory. Conventional hydrocycloning and gravity concentration methods were found to be ineffective due to the fine dissemination and encapsulation of tin mineralization, with more than 99% of the tin reporting to gravity separation tailings. In the untreated material, tin mineralization is predominantly represented by cassiterite, as confirmed by electron microscopy and energy-dispersive X-ray microanalysis. Thermal activation at 450 °C under oxygen-free conditions was shown to induce profound transformation of the original cassiterite mineralization. Cassiterite was not detected in the thermally activated products; instead, newly formed multiphase aggregates containing tin, bismuth, iron, silicon, aluminum, carbon, and oxygen were identified. These aggregates exhibit characteristic film-globular morphologies ranging in size from 1–3 to 100–200 μm. As a result of thermal treatment, tin concentrations in the thermal products increased to 1500–1864 g/t, corresponding to ore-grade levels. The obtained results demonstrate the potential of thermal activation as an effective approach for the utilization of previously low-grade tin-bearing weathering crusts and for expanding the tin mineral resource base of Kazakhstan.