Upcycling Electroplating Sludge into NiO/CaO Catalysts: A Waste-to-Value Approach for High-Performance CO ₂ Gasification of Biochar

Nickel-rich electroplating sludge, a hazardous waste generated by the electroplating industry, exhibits significant recycling potential and economic value. The use of electroplating sludge to prepare catalysts for CO2 capture and biochar gasification has rarely been reported. In this study, a sustainable method is proposed for recovering Ni-containing electroplating sludge by synthesizing Ni-CaO composite metal oxide catalysts, which enhance the catalytic gasification of biochar with CO2. The effects of various reaction conditions on CO release and CO2 conversion rates were systematically investigated. According to the results, the optimized Ni-CaO-2 catalyst (30 wt % loading) exhibited outstanding catalytic performance, achieving a peak CO release rate of 114.8 mL/min/g and a CO2 conversion rate of 62.3% at 850 °C, which was 1.6 times that of the conventional CaO catalyst. The incorporation of Ni improved gasification performance through the redox effect of Ni2+/Ni3+, which induced the formation of oxygen vacancies, thereby promoting CO2 activation. This approach not only facilitates the recycling of hazardous electroplating sludge but also contributes to carbon emission reduction, providing a sustainable strategy for waste utilization and environmental protection.