Recovery of residual carbon from coal gasification fine slag by a combined gravity separation-flotation process

Recovering inner residual carbon is important for fully utilizing coal gasification fine slag (CGFS) resources. In this study, we adopted a combined gravity-separation and flotation process to efficiently recover residual carbon by considering the characteristics of the CGFS and optimizing the operating factors of the process. CGFS is principally a mixture of residual carbon and ash, with low-density particles containing more of the former. Accordingly, residual carbon is preliminarily enriched by gravity separation, in which gas velocity ( v g ) and water velocity ( v w ) significantly impact separation efficiency, followed by feed volume ( m ). The residual carbon in the initial concentrate was preliminarily enriched (i.e., loss on ignition ( LOI ): 55.90%; combustible recovery ( R o ): 72.36%) under appropriate operating conditions (i.e., v w  = 0.04 m/s, v g  = 3 m/s, m  = 150 g). Moreover, the quality of the flotation concentrate was most influenced by collector dosage ( m c ), followed by aeration rate ( η ), frother dosage ( m f ), stirring speed ( w ), and grinding time ( t ) during flotation of the primary concentrate. The flotation concentrate exhibited LOI and R o values of 90.95% and 50.34%, respectively, under the optimal flotation conditions (i.e., m c  = 20 kg/t, m f  = 15 kg/t, w  = 2600 rad/min, η  = 200 L/h, t  = 360 s); it has a high residual carbon content and is an ideal raw material for preparing fuels or carbon materials.