Plant rejects disposal strategies applied at Caval Ridge open cut coal mine
Co-disposal of tailings and coarse wastes
Caval Ridge Mine (CVM) is one of the newly established open-cut coal mines of BHP in Queensland, where no tailings dam was allowed to be built to minimise environmental impacts from mining activities. The waste streams from the coal washing and handling process (CHPP), including dewatered fine tailings through belt filter press process (BFT), coarse rejects and mixed plant rejects (MPR), have to be co-disposed within waste dumps built with pre-strip and dragline spoil. Due to low yield (40 – 60%) and low spoil to reject ratio (< 5) large quantities of rejects bring significant geotechnical and operational challenges at CVM, which are exacerbated by increased annual production rates and additional rejects from washing coal from an adjacent mine. Further in-house geotechnical review commenced in middle 2014 based on the initial geotechnical studies during the project stage of CVM between 2011 and 2013. The outcomes have maximised rejects disposal at CVM by constructing large BFT cells, coarse rejects only dumps, and co-disposal of MPR at dump tip heads.
This paper is to present the rejects disposal strategies at CVM from both technical and operational aspects. The paper will also discuss future projects for BFT moisture reduction, tailings clay mineralogy, as well as MPR co-disposal verification and optimisation.