Thermal detoxification of hazardous metal sludge by applied electromagnetic energy

Industrial wastewater sludge was treated by microwave processes to enhance the stabilization of laden copper. The effects of additives, processing time, microwave adsorbents, moisture content, reaction atmosphere, and cooling gas were investigated. The stabilization results were significantly enhanced by metal powder additives, prolonged microwave processing time, proper moisture content, the addition of carbonaceous materials, and a reaction environment with inert gas. It was also found that the moisture content would increase the homogeneity of applied microwave energy, and thus achieve a better overall efficiency between stabilizing agents and copper. The added metal powders may reduce Cu(II) to Cu(0) in the sludge or TCLP. The resulting thermal energy of microwave radiation, and microarcing process and the oxidation heat of Al powder may also assist the transformation of Cu(II) into CuO and CuAl₂O₄ phases. Part of the sludge was vitrified within inert gas environment when the processing time was longer than 18 min and active carbon dosage was more than 3 g. Reduction reactions also occurred in the hybrid microwave processes, leading to the reduction of sulfates and metal ions, and the formation of Cu₂S and FeS. Moreover, the microwave radiation can also enhance the feasibility of co-treating of inorganic and organic solid waste.