Rita Kallio

Several research projects are currently focused on the search for new sources of scandium due to its expected increasing demand in advanced technology applications. The Kiviniemi Fe-Sc-enriched mafic intrusion is a potential primary source for Sc. According to the recent investigations on the FeO component reduction in the Kiviniemi magnetic Sc concentrate at various end temperatures, complete FeO reduction is achieved at the highest experimental temperature (1500 °C). However, efficient separation of metal from the Sc₂O₃-enriched slag is hindered by the high viscosity of the slag. In this study, investigations of the Kiviniemi-type concentrate reduction characteristics are complemented from three perspectives: (1) slag modification with CaF₂ and/or CaO to promote the reduction of the FeO component and metal separation, (2) reduction characteristics of the concentrates with a slightly different modal mineralogy and chemical composition, and (3) description of the main features of the progression of reduction at selected temperatures (950, 1050, 1150, 1250, and 1350 °C) with CaO addition. Both CaF₂ and CaO increase conversion rates at a lower temperature region and promote the separation of metal from the slag. High-temperature behavior of the concentrates used in this study is essentially similar, although the main reduction stage is initiated at a slightly higher temperature for concentrates with less amphibole and a higher amount of nonferrous gangue minerals. Only after the complete decomposition and melting of clinopyroxene and nonferrous minerals of the concentrate, the final reduction of the FeO component from the slag can take place.

Scandium is classified as a critical raw material by the European Union. Its beneficiation from various primary and secondary sources is currently being studied under several research and development projects. Due to the geochemical characteristics of Sc, its enrichment to ore grades by geological processes is scarce. Potential new sources are investigated to respond to the expected increasing demand for this rare earth metal. The recently discovered Kiviniemi Sc deposit in Finland represents an igneous occurrence with estimated total resources of 13.4 Mt and an average Sc grade of 163 g/t. The deposit consists of relatively homogeneous ferrodioritic intrusive body with its main unit with ~2.5 ha surface extension. Scandium is mainly incorporated into the lattice of clinopyroxene and amphibole within the main unit. Composite samples from three drill cores from various parts of the main unit were concentrated with a combination of low-intensity and high-gradient magnetic separation. Depending on the feed characteristics, high-gradient magnetic separation reached recoveries between 87% and 92% with 230–310 ppm Sc while removing 35–49 mass percent of gangue minerals, mainly plagioclase and potassium feldspar. Our study provides information on the magnetic preconcentration conditions with process mineralogical details and produced concentrates for further testing according to the suggested processing scheme.