Mineralogical and physical studies of low-grade tantalum-tin ores from selected areas of Rwanda

Abstract

In this work, mineralogical and physical characterization of low-grade tantalum-tin ore-samples from Ntunga and Kamonyi of Rwanda were carried out using various techniques. The ore-samples were classified as low-grade and non-radioactive ores as they contained less than 0.1% Ta2O5 and Nb2O5, and the percentage of radioactive oxides were below the critical value of 0.5%. The characteristic elements associated with tantalum as detected and quantified by Inductively Coupled Plasma-Optical Emission Spectroscopy and expressed as oxides for their natural occurrence included Ta2O5, Nb2O5, Fe2O3, MnO, SnO2, MgO, TiO2, U3O8, and ThO2, among others. Analysis of samples in raw form showed presence of valuable minerals of cassiterite (0.067%–0.469%), and columbite-(Fe) with Nb2O5 (0.050%–0.062%) and Fe2O3 (0.194%–0.769%), and tantalite-(Mn) with Ta2O5 (0.039%–0.063%) and MnO (0.080%–0.186%). Upon a rough gravity concentration, the ore-samples resulted in concentrate with compositions of 66.14%SnO2, 7.66%Ta2O5 and 7.70%Nb2O5. These minerals with most particle sizes of 125 μm were disseminated within the alumino-silicate matrix of the pegmatite rock. All samples showed nearly similar mineralogical compositions, and the XRD results strongly supported this observation, with diffractograms showing identical characteristic peaks which matched mainly with kaolinite, muscovite, and quartz minerals. Peaks of cassiterite, columbite and tantalite were not strong and visible but upon concentration, they became clear, sharp, and strong. These results will serve as a baseline for selecting and designing appropriate processing technique to effectively harness this mineral resource.