Deep recovery of clean coal from coking middlings: Pre-separation in liquid-solid fluidized bed and subsequent flotation

The coking middlings remaining after the production of coking coal contain a significant amount of clean coal, which has the high economic and environmental value if it can be effectively enriched. To improve resource utilization and avoid the negative environmental impacts of coking middlings, this study evaluated a new comprehensive separation process (i.e., pre-gravity separation in liquid-solid fluidized bed and subsequent flotation) to achieve high-yield recovery of clean coal from coking middlings. Preliminary enrichment by gravity separation achieved a combustible recovery rate, a clean-coal yield, and an ash content of 64.43 %, 49.62 %, and 15.89 %, respectively. This product was ground for 20 min to further dissociate clean coal and inorganic minerals and was further enriched by flotation separation. Under optimal flotation conditions (rotational speed, 2200 rpm; mass of collector, 2 kg/t; mass of frother, 200 g/t; and pulp concentration, 40 g/L), a clean-coal combustible recovery rate of 84.19 % was achieved. Overall, the comprehensive separation process achieved a clean-coal product with a high yield of 38.82 % and low ash content of 9.08 %, which is suitable for use as coking coal for steel plants. The tailings, with an ash content of 51.49 % and a yield of 61.18 %, are suitable as fuel for power plants. Therefore, the comprehensive separation process provides good economic benefits.