Grinding activation effect on the flotation recovery of unburned carbon and leachability of rare earth elements in coal fly ash

Coal fly ash (CFA) as a secondary resource has received a great deal of attention over the past few decades. Research on rare earth elements (REEs) and unburned carbon removal by flotation from CFA is burgeoning, respectively. It will be beneficial if REEs could be rich in the flotation product with the carbon removal. In this study, the optimization of flotation for the unburned carbon removal was investigated and near 100% removal came true with loss on ignition of 56% and the yield of 7.7%. The optimal conditions contain rotation speed of 600 rpm and time of 30 min using the collector of 1200 g/t, the frother of 140 g/t, and the density of 130 g/t for the flotation. The majority of REEs occurred in the tailing after the flotation due to the low yield and REEs contents of the concentrates. The difference of REEs distribution in the tailing and concentrate is more significant in the milled sample. The morphology was also observed to explain the microscale behavior of REEs during the flotation. [Display omitted] •Flotation-acid leaching combined process is proposed to recovery of unburned carbon and REEs in CFA.•Different operation parameters are studied in flotation-leaching system.•The main factors causing the floatability of CFA were found and discussed.•Grinding can effectively remove unburned carbon and enrich REEs in flotation tailings.