Environmental impact and carbon recovery in coal gasification slag after Separation-Oxidation-Acid washing (SOA) process.

Coal gasification slag (CGS) is a challenging solid waste due to the presence of highly toxic heavy metals, which pose significant risks to environmental and human health. CGS cannot be freely reused or disposed of, creating considerable obstacles to solid waste resource utilization. This study presents a novel method for heavy metal removal from CGS through a separation-oxidation-acid washing (SOA) process, which effectively recycles residual carbon (RC) while minimizing the risk of heavy metal leakage. The chemical morphology, leaching patterns, and environmental risks of heavy metals in CGS following the SOA process were investigated, demonstrating effective separation and removal. The ignition loss (LOI) in CGS exceeded 45% after treatment, significantly surpassing the original value. Removal rates for Sb, Pb, and As from coal gasification fine slag (CGFS) were 88.6%, 75.88%, and 79.35%, respectively, while rates for Sb, As, and Ni from coal gasification coarse slag (CGCS) were 56.65%, 63.24%, and 50.8%. The risk assessment codes (RAC) for Cu, Co, and Sb in CGFS were reduced to low-risk levels of 3.18%, 10.30%, and 25.21%, respectively, and the relative leaching ratios (RLR) for Co (0.162%), Cu (0.006%), and Ni (0.180%) in CGCS exhibited notable reductions, suggesting that the applied process significantly mitigates the environmental risk and leaching potential of these heavy metals. Overall, this study contributes to the clean production of coal gasification enterprises by offering an environmentally friendly strategy for heavy metal removal and enhancing resource utilization through RC recovery.