Assessment of brownmillerite and periclase hydration in chromite ore processing residue at elevated temperature

Abstract

Chromite ore processing residue (COPR) is a solid waste that was generated by the high temperature process of chromium extraction from chromite ore using soda ash and lime. The purpose of this study was to evaluate whether brownmillerite and periclase could be transformed into other minerals to understand and predict phase transformation during weathering in COPR. In this study, brownmillerite hydration to hydrogarnets and periclase to brucite in COPR materials were respectively assessed at elevated temperatures (100°C and 200°C) for 30 days because these reactions are very slow at ambient temperatures. The results showed that no apparent phase transformation was observed at 100°C. However, brownmillerite and periclase started dissolving the first day at 200°C, forming hydrogarnets and brucite, and completely dissolving after 15 days. Moreover, hydrogarnets were the main phase after 30 days of reaction. This indicated that the phase transformation could be possible when the initial COPR materials with high content of brownmillerite are exposed to long-term weathering.