Enrichment characteristic and leaching risk of harmful elements in carbon-ash separation products of coal gasification fine slag

Carbon-ash separation is a prerequisite for efficiently utilizing coal gasification fine slag (CGFS), but the enrichment characteristics of harmful elements (HEs) in the separation process are not fully understood. This paper uses gravity separation to prepare different samples, and four typical HEs (Se/Cd/Pb/Cr) in separated products were investigated. The results showed that samples with an ash yield of 28.72%–98.86% and a specific surface area of 12.90 m²/g-389.51 m²/g were obtained through gravity separation. The highly volatile element Se was enriched in the C-C/C-H structure of residual carbon under the catalysis of acidic gases. The nonvolatile element Cr was encapsulated by low-melting-point minerals and remained in the minerals. The semi-volatile element Cd/Pb was easily enriched in a particle with a high specific surface area/large pore volume, especially in porous residual carbon, with an enrichment factor as high as 7.0 and 4.0, respectively. The leaching risk analysis of sorted products indicates that the products were not suitable for direct landfill; however, besides honeycomb porous carbon, other highly specific surface area products can be safely used for soil improvement. The results of this study are expected to provide a reference for the classification and utilization of CGFS and the control of HE pollution.