Reduction characteristics of Kiviniemi ferrous scandium concentrate

Abstract

• The main reduction stage of ferrous Kiviniemi concentrate is initiated at ∼ 950 °C. • Derivative conversion rates increase sharply from 1050 °C with high rates until ∼ 1250 °C. • Complete reduction of FeO is achieved at 1500 °C. • The properties of the resulting slag will need to be modified to promote metal separation. Scandium provides technological advantages particularly in solid oxide fuel cells and aluminum alloys. Potential new sources are investigated to respond to the expected increasing demand of this rare earth metal, which is currently classified as a critical raw material for the European Union. The recently discovered Kiviniemi mafic intrusion in Finland has been estimated to contain a total resource of 13.4 Mt of Sc with an average grade of 163 g/t. At Kiviniemi, Sc is incorporated within the lattices of ferrous silicates. Magnetic separation has been proposed as the first processing step to lower the amount of alkali-bearing diamagnetic minerals in Kiviniemi concentrates. Pyrometallurgical processing is suggested as the second step to decrease the amount of the ferrous oxide component from the concentrate prior hydrometallurgical processing. This study presents the first results of thermogravimetric experiments on pyrometallurgical reduction of the Kiviniemi concentrate up to temperatures of 1350–1500 °C. The aim of the study was to investigate the progression and extent of ferrous oxide reduction in the concentrate and to characterize the properties of resulting Sc-enriched slag and metal. The main reduction stage is initiated at ∼ 950 °C with a sharp increase in the derivative conversion rates between 1050 and 1170 °C and high rates until ∼ 1250 °C. Although complete reduction of FeO is achieved, the segregation of metal from the highly viscous slag will need to be promoted by adjusting the viscosity of the slag prior hydrometallurgical experiments.