Co-Valorization of Electroplating Sludge and Water-Washed MSWI Fly Ash for the Preparation of Black Ceramic Glaze

(1) Background: Electroplating sludge (ES) and water-washed municipal solid waste incineration fly ash (WFA) are classified as hazardous solid wastes, and their conventional disposal approaches trigger severe heavy metal pollution. Conventional colored ceramic glazes heavily depend on virgin mineral ores and synthetic colorants; therefore, sustainable alternative feedstocks are urgently required. (2) Methods: WFA and ES were compounded with red clay and shale to fabricate low-environmental-risk black glazes. Material microstructures and phase compositions were characterized via X-ray diffraction (XRD) and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). Single-factor experiments were conducted to optimize the raw material ratios and sintering schedules, while heavy metal leaching toxicity was evaluated following national standard HJ/T 300-2007. (3) Results: The optimal composite formulation consists of 26.1 wt% WFA, 30.4 wt% ES, 26.1 wt% red clay and 17.4 wt% shale. Smooth, defect-free pure black glaze specimens were fabricated after sintering at 1280 °C for 90 min under a weak reducing atmosphere. Heavy metal ions were stably immobilized within the silicate crystalline and amorphous glass phases, with all leaching concentrations well below the national standard thresholds. (4) Conclusions: The proposed technology achieves the high-value co-valorization of two hazardous solid wastes while producing low-environmental-risk colored ceramic glazes, providing a feasible strategy for solid waste recycling and the low-carbon development of the ceramic manufacturing industry.