There are a few current projects investigating primary and secondary sources of scandium, which is listed as a critical raw material for EU. Kiviniemi mafic intrusion in Finland is a potential primary Sc deposit with preliminary estimate of 13.4 Mt ferrous rocks with 163 ppm Sc. Due to the challenges in separation of Fe and Sc in hydrometallurgical processing of ferrous Sc concentrate, pyrometallurgical reduction of ferrous component has been conducted and Sc2O3-enriched slag has been produced at a laboratory scale.
The Geopyörä test has been used to characterize the breakage properties of two slag samples from Kiviniemi concentrates. Since it uses smaller samples and can rapidly estimate standard comminution parameters with good accuracy, it was a better alternative than traditional tests. This case study presents the methodology and obtained results, which indicated that the slag material is friable/brittle, but moderately hard to grind below 150 microns or finer.
There is no domestic primary production of scandium (Sc) in the European Union; therefore, this metal is currently classified as a critical raw material with a very limited, highly concentrated supply base (Blengini et al., 2020). Hence, new Sc sources are required that can provide the foundation for a more stable market and help increase the use of scandium in high-technology applications (Bobba et al., 2020; Blengini et al., 2020). To respond to the lack of Sc supply and its expected increasing demand, potential new sources of Sc are investigated from various primary and secondary resources (Botelho Junior et al., 2021). One example of potentially exploitable Sc mineralization is the recently discovered Sc deposit associated with the Kiviniemi mafic intrusion in eastern Finland.
The Kiviniemi mafic intrusion (1857 ± 2 Ma) locates in the municipality of Rautalampi, approximately 70 km southwest of the city of Kuopio (Halkoaho et al., 2020; Hokka & Halkoaho, 2016). As stated by Halkoaho et al., (2020) it occurs near the eastern margin of the Paleoproterozoic Central Finland Granitoid Complex (CFGC) and is associated spatially and temporally with postkinematic Fe-Ti-P-enriched Svecofennian orogenic mafic magmatism. The main relatively homogeneous ferrodioritic unit has a surface extension of ~2.5 hectares with an additional small satellite body. During drilling programs between 2008 and 2010 altogether nine holes were drilled at Kiviniemi. Medium- to coarse-grained garnet-bearing fayalite ferrodiorite bodies, enriched in Fe and Sc, are surrounded by transitional ferrodiorites and pyroxene ferromonzodiorites. The country rock is porphyritic granite.
An average Sc grade of 163 g/t with 1726 g/t Zr and 81 g/t Y have been reported for mineral resource of 13.4 Mt, which represents a preliminary estimate calculated with the inverse distance method (Hokka and Halkoaho, 2016). Ferrous amphibole and ferrohedenbergite are the main carriers of Sc. To overcome the harmful issues introduced by Fe to the hydrometallurgical processing of Kiviniemi concentrate, a three-stage processing scheme is suggested for Kiviniemi-type deposits (Fig. 2). It introduces a preconcentration stage with conventional magnetic methods (LIMS + PHGMS) followed by pyrometallurgical treatment to reduce the ferrous oxide component prior to hydrometallurgical processes.