Multi-Analytical Characterization of Slags to Determine the Chromium Concentration for a Possible Re-Extraction

• Main Authors: Liesbeth Horckmans, Robert Möckel, Peter Nielsen, Frantisek Kukurugya, Christine Vanhoof, Agnieszka Morillon, David Algermissen
• Format: Article
• Language: English
• Published: MDPI AG 2019-10-01
• Series: Minerals
• Subjects: steel slag; ferrochromium slag; chromium extraction; multi-analytical characterization; method comparison
• Online Access: https://www.mdpi.com/2075-163X/9/10/646

The CHROMIC project (effiCient mineral processing and Hydrometallurgical RecOvery of by-product Metals from low-grade metal contaIning seCondary raw materials) aims to recover chromium from steelmaking and ferrochrome slags to regain valuable resources and simultaneously reduce potential environmental impacts. To develop the recovery flowsheets and reliably calculate metal recovery, an accurate assessment of chromium concentration and distribution is essential. Therefore, model streams were thoroughly characterized using a combination of analytical techniques. In all materials, chromium is present in distinct but often small spinel phases, intergrown with other minerals and showing a considerable zonation in Cr content with higher amounts in the cores. The small size of the Cr-rich particles makes recovery by mineral processing challenging. Measured chromium content was found to differ largely based on the chemical dissolution method applied. The analysis of insoluble residues and comparison with a standard reference material evidenced that standard acid dissolution procedures based on HCl/HNO₃/HBF₄ and HNO₃/HF/H₂O₂ are insufficient to fully dissolve spinel structures, leading to severe underestimations of chromium content. A sodium peroxide treatment is required for a full dissolution of spinels. This is noteworthy, since most of the legislation for the reuse of slags is currently based on acid dissolution methods.