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

Horckmans Horckmans,Morillon Morillon,Möckel Möckel,Nielsen Nielsen,Kukurugya Kukurugya,Vanhoof Vanhoof,Algermissen Algermissen

doi:10.3390/min9100646

Abstract

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.

Highlights

Slags are an integral part of steel and ferrochrome (FeCr) production, as they capture impurities so that high-quality metals can be produced
The results show that the chemical composition of low-carbon ferrochrome slags (LC FeCr) and SS is quite similar, with Ca, Mg, and Si as the main elements
Cr quantification accurate Cr determination from the solution, but insoluble residues strongly depending on correct phase identification, backcalculated

Summary

Introduction

Slags are an integral part of steel and ferrochrome (FeCr) production, as they capture impurities so that high-quality metals can be produced. Steelmaking slags are commonly divided into basic oxygen steelmaking (BOS or BOF), electric arc furnace (EAF), and ladle slags based on the method of production, as detailed in [1,2]. In Europe, 18.4 Mt of steelmaking slags were produced in 2016, of which 57% are BOS, 7.3% are EAF stainless steel slags (SS), and 25% are EAF carbon steel slags (CS) [3]. Slag production varies according to the type of FeCr produced. High-carbon ferrochrome (HC FeCr) produces 1.1–1.6 tons slag/ton of metal [4,5] with an annual global production of 13 Mt HC FeCr in 2018 [6]. Slag production is relatively higher for low-carbon ferrochrome

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Conclusion