Co-processing of multi-source solid wastes in a coal-water slurry gasifier: Heavy-metal emissions, distribution and...

Co-processing multi-source hazardous solid wastes in coal-water slurry gasifiers (CWSGs) presents a promising waste-to-energy strategy, yet the migration behavior and environmental fate of heavy metals within this high-temperature reducing atmosphere remain poorly understood. This industrial-scale study investigated the emission, partitioning, and environmental risks of Ba, Zn, Ni, Mn, Cr, and Pb during the co-processing of anthraquinone dye, distillation residue, and spent activated carbon. Results demonstrated that solid waste introduction was operationally favorable, increasing syngas output by 7.4 % and temperature by 5.9 %. Notably, the system achieved metal retention, with volatilization rates remaining extremely low due to dual immobilization mechanisms: non-volatile metals (e.g., Cr) were stabilized into high-melting-point mineral phases (e.g., CaCr₂O₄), while volatile metals (Pb, Zn) followed a volatilization-condensation pathway, rapidly transferring from syngas to the liquid phase. A critical divergence in environmental risk was observed between slag types; while coarse slag effectively immobilized metals in stable residual fractions, fine slag (CGFS) exhibited alarming mobility (>97 %) for Mn, Ni, and Zn, with Ni classified as high risk. These findings validate CWSG co-processing as an environmentally secure technology for hazardous waste destruction, provided that specific downstream management strategies are implemented for the heavy metals enriched in fine slag.