Carbon-ash separation of coal gasification fine slag by flocculation-flotation process

Coal gasification slag (CGFS), which was a bulk solid waste in coal chemical industry, shows great application potential in the preparation of silica microspheres, zeolites ceramic materials, etc. However, its high residual carbon characteristics hinder to its development. Decarburization is a necessary precondition for the effective utilization of CGFS. The efficient separation of carbon or ash from CGFS remains a challenge due to its ultra-fine particle size. This work provides a novel flocculation-flotation process to achieve the complete carbon-ash separation of CGFS. The addition of anionic polyacrylamide (APAM) or polyethylene oxide (PEO) had positive effect on the flotation of CGFS, especially for APAM. With APAM dosage of 50 g/t, the ash content of carbon slag and ash slag were 59.04% and 97.11%, respectively. In this process, the zeta potential of carbon slag and ash slag decreased from -17.43 and -11.77 mV to -23.45 and -29.80 mV, respectively. The greater change of zeta potential of ash slag indicates its stronger adsorption of APAM, leading to the higher flocculation trend of ash particles than that of carbon slag. APAM has selective flocculation effect on ash slag, which contributed to reduce the mechanical entrainment during flotation, thereby achieving complete carbon-ash separation of CGFS.