Multidisciplinary study of the beneficiation potential of the Kiviniemi ferrous scandium deposit

In this study, laboratory-scale experiments have been conducted to investigate the beneficiation possibilities of Kiviniemi ferrous scandium deposit to respond to the expected increasing demand of Sc. Kiviniemi is a recently discovered Sc deposit associated with mafic intrusion in eastern Finland; it can be regarded as a potential Sc deposit with a preliminary mineral resource estimate of 13.4 Mt with an average Sc grade of 163 g/t. In Kiviniemi, Sc is mainly incorporated into the lattices of ferrous clinopyroxene and amphibole, which makes the beneficiation very challenging. To release Sc from ferrous silicates, the following 3-stage processing scheme has been investigated: 1) magnetic separation to decrease the amount of alkali-containing diamagnetic minerals and produce ferrous concentrate enriched in Sc; 2) pyrometallurgical reduction of the ferrous component from the magnetic concentrate, and 3) hydrometallurgical extraction of scandium from the iron-depleted slag.
Magnetic separation resulted in 32–45 mass% reduction of diamagnetic, alkali-containing minerals from the feed and only negligible losses of scandium to the tailings. Moderate additions of CaO were shown to improve the reduction characteristics and segregation of metallic iron from the Sc-enriched slag. Although the risk of gelation was avoided by the sulfuric acid-based leaching of the produced slag, the efficiency of leaching remained at best at the level of 40−50%. However, the obtained results provide a foundation for further investigations on the beneficiation possibilities of Kiviniemi-type ferrous scandium deposits. Further studies could include modification of slag properties to improve the potential for selective leaching and/or further investigations of the direct hydrometallurgical extraction of Sc from the concentrates, provided a control over Fe dissolution could be established.