Washability evaluation of coal gasification slag via an integrated sieving-water flow classification

Washability evaluation and effective recovery of residual carbon from coal gasification slag (CGS), including fine slag (FS) and coarse slag (CS), is essential for the cascade utilization and precise valorization of the solid waste. This work focuses on the washability evaluation of a typical FS and CS sample through an integrated sieving-water flow classification strategy. The results found that residual carbon was mainly concentrated in the larger particle size fractions, specifically, in particles larger than 75 μm of FS, and in particles larger than 125 μm of CS. Via the integrated sieving-water flow classification process, the residual carbon could be recovered effectively and the loss on ignition (LOI) of the floats in the +75 μm fraction of FS reached 82.62% with a comprehensive efficiency of 42.78%; the LOI of the floats in the +125 μm fraction of CS attained 82.93% with a comprehensive efficiency of 71.78% under the optimized conditions. The washability curves of FS and CS were constructed and exhibited favorable reliability, thereby allowing a targeted selection of optimal parameters of water flow classification according to the practical product requirements. For the direct water flow classification process, the fine particles could also be separated, while the limited enrichment in LOI of the floats caused the low recovery efficiency. This study provides a novel and efficient method for enriching residual carbon from CGS and offers a practical reference for rapidly evaluating separability and selecting appropriate separation conditions in future applications.