Unsaturated characteristics and transport of hydrated chromium ore processing residue

Abstract

A mining tail cover system for controlling toxic substances (e.g. chromium (VI) (Cr6+)) in chromium ore processing residue (COPR) requires unsaturated transport modelling with inputs of water retention curves (WRCs) to evaluate the system. This study experimentally characterised the unsaturated properties of unweathered grey-black (GB) and weathered hard-brown (HB) COPR before and after hydration associated with mineralogical changes and estimated chromium transport by employing numerical modelling with the properties. X-ray diffraction (XRD) tests were also performed before and after testing to quantify the mineralogical compounds of materials. The XRD results showed that the brownmillerite decreased with the degree of the hydration. The relationship between the fitting parameters of WRC models and variables, such as the degree of hydration and specific gravity, was investigated. The WRC of GB COPR shows a bimodal shape because of the hydration process during the test. The hydration process transformed the chemical and mineralogical composition of GB COPR, thus influencing its WRC characteristics. Numerical simulations parameterised by WRC properties were conducted to compare unsaturated transport between GB and HB COPR through a sandy cover. HB COPR had a longer transportation time than GB COPR, revealing the importance of considering water retention characteristics in remediation plans.