Effective separation of coal gasification fine slag: Role of classification and ultrasonication in enhancing flotation

Effective separation of residual carbon and ash is the basis for the resource utilization of coal gasification fine slag (CGFS). The conventional flotation process of CGFS has the bottlenecks of low carbon recovery and high collector dosage. In order to address these issues, CGFS sample taken from Shaanxi, China was used as the study object in this paper. A new process of size classification − fine grain ultrasonic pretreatment flotation (SC-FGUF) was proposed and its separation effect was compared with that of whole-grain flotation (WGF) as well as size classification − fine grain flotation (SC-FGF). The mechanism of its enhanced separation effect was revealed through flotation kinetic fitting, flotation flow foam layer stability, particle size composition, surface morphology, pore structure, and surface chemical property analysis. The results showed that compared with WGF, pre-classification could reduce the collector dosage by 84.09% and the combination of pre-classification and ultrasonic pretreatment could increase the combustible recovery by 17.29% and up to 93.46%. The SC-FGUF process allows the ineffective adsorption of coarse residual carbon to collector during flotation stage to be reduced by pre-classification, and the tightly embedded state of fine CGFS particles is disrupted and surface oxidizing functional group occupancy was reduced by ultrasonic pretreatment, thus carbon and ash is easier to be separated in the flotation process. In addition, some of the residual carbon particles were broken down to smaller sizes in the ultrasonic pretreatment, which led to an increase in the stability of flotation flow foam layer and a decrease in the probability of detachment of residual carbon particles from the bubbles. Therefore, SC-FGUF could increase the residual carbon recovery and reduce the flotation collector dosage, which is an innovative method for carbon-ash separation of CGFS with good application prospect.