University of Oulu

Kallio, R., Lassi, U., Kauppinen, T., Holappa, E., Christophliemk, M., Luukkanen, S., Tanskanen, P., & Fabritius, T. (2022). Leaching characteristics of Sc-enriched, Fe-depleted acidic slags. Minerals Engineering, 189, 107901.

Leaching characteristics of Sc-enriched, Fe-depleted acidic slags

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Author: Kallio, Rita1; Lassi, Ulla2,3; Kauppinen, Toni2,3;
Organizations: 1University of Oulu, Faculty of Technology, Oulu Mining School, PO Box 3000, FI-90014, Finland
2University of Oulu, Faculty of Technology, Sustainable Chemistry, PO Box 3000, FI-90014, Finland
3Kokkola University Consortium Chydenius, University of Jyvaskyla, PO Box 567, FI-67101, Finland
4University of Oulu, Faculty of Technology, Process Metallurgy, PO Box 3000, FI-90014, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 10.1 MB)
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Language: English
Published: Elsevier, 2022
Publish Date: 2022-11-14


Scandium is currently classified as a critical raw material for the European Union, and several research projects focus on the search for new sources to supply to its expected increasing demand. The Kiviniemi mafic intrusion in Finland is a potential primary source for Sc; at Kiviniemi, Sc occurs mainly within the lattices of ferrous silicates, clinopyroxene and amphibole. Some of the main challenges in leaching of Kiviniemi-type feed material are related to either the complexity of Fe and Ti separation from Sc-containing solutions or a possible gelation problem when leaching a material with a high SiO₂ content. According to preliminary beneficiation tests, direct acid leaching of the Kiviniemi feed material was not successful mainly due to extensive leaching of Fe from the ferrous concentrate. Therefore, a processing scenario with conventional magnetic separation followed by pyrometallurgical reduction of the FeO component to tackle the Fe issue prior hydrometallurgical stage was studied in the previous parts of our project. Leaching experiments in this study focus on the possibilities to extract Sc from low-FeO, Sc₂O₃-enriched amorphous slag. Both a synthetic slag and slags produced from Kiviniemi concentrates were submitted to H₂SO₄-based leaching experiments applying dry digestion, H₂O₂-assisted leaching, and high-pressure acid leaching (HPAL). The formation of silicic acid (gelation) under acidic conditions was avoided with all these methods. With H₂O₂-assisted leaching, efficiencies reached 40–50%, whereas leaching with dry digestion was very limited. With HPAL, the leaching efficiency remained at 30–45% under experimental conditions of 2.5 M H₂SO₄, 60 bar, and 150 °C. These levels of leaching efficiencies are due to an amorphous structure and high SiO₂ content of the slag. Future options for hydrometallurgical processing of Kiviniemi-type slags could include controlled cooling of the slag to produce crystalline structures, combined potentially with further chemical modification to enable selectivity for leaching.

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Series: Minerals engineering
ISSN: 0892-6875
ISSN-E: 1872-9444
ISSN-L: 0892-6875
Volume: 189
Article number: 107901
DOI: 10.1016/j.mineng.2022.107901
Type of Publication: A1 Journal article – refereed
Field of Science: 215 Chemical engineering
Funding: This research has been funded by the K.H. Renlund Foundation and The Foundation for Research of Natural Resources in Finland, grant number 20210019.
Copyright information: © 2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY license (