Combined gravity separation-oil agglomeration separation of coal gasification fine slag and metal elements risk characteristics in separated products

Coal gasification fine slag (FS) is a by-product of coal gasification with significant potential for resource utilization. However, the low recovery rate of residual carbon greatly restricts its resource utilization and harmless disposal. In this paper, a spiral separator was used to recover FS, followed by the use of oil agglomeration separation technology to enhance the selection of concentrate. The separation mechanism of the oil agglomeration process was analyzed through EDLVO theoretical calculation. Finally, the ecological risk of metal element speciation in the separated products was assessed with Risk Assessment Code (RAC) and the Ratio of Secondary Phase to Primary Phase (RSP). The results showed that by optimizing the separation parameters, efficient separation of residual carbon and ash components could be achieved at the pulp flow of 1.0 m³·s⁻¹ and pulp density of 5%, with the ash content of the obtained concentrate, middlings, and tailings products being 42.11%, 40.45%, and 88.46%, respectively. Concentrates were reselected using oil agglomeration separation technology at the oil dosage of 25% and a stirring time of 15 min, and the ash content of the obtained clean coal and tailings were 18.04% and 93.04%, while the clean coal yield of this grade accounted for 38.48% of the total sample. The EDLVO theory indicated that the emulsified kerosene enhanced the hydrophobicity of the residual carbon particles, increasing the difference in hydrophobicity between the carbon and ash particles, thereby strengthening the recleaning effect of concentrate. The RSP evaluation method confirmed that metal element levels in tailings are within safe limits, which could be used for direct secondary resource utilization. This study provided a theoretical basis and technical guidance for the separation and resource utilization of FS.