Technical note Cr(VI) generation during milling

Abstract

An investigation of the dry milling of chromite at a ferroalloy producer revealed high Cr(VI) concentrations in the milled ore. This promted further investigation into the possible generation of Cr(VI) during milling. Experiments conducted in the laboratory proved that Cr(VI) is generated during dry milling. This fact implies that the health of workers on and around such milling installations could be compromised. Leaching of Cr(VI) from settled dust originating from dry mills could also lead to soil and groundwater contamination. Due to the vast differences in toxicity of Cr(III) and Cr(VI), chemical analysis is often required to distinguish between these two oxidation states. However, pulverising or milling of samples during sample preparation, which is common practise for solids, could lead to misleading analytical results. This investigation proved that even material that initially contained no Cr(VI) could be regarded as toxic if treated incorrectly.