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.