Stabilization of Cu in acid-extracted industrial sludge using a microwave process

The leaching concentration of copper ions from the industrial sludge that has been extracted using sulfuric acid may still exceed 15 mg/L, which is the leaching standard of the toxicity characteristic leaching procedure (TCLP) for hazardous waste in Taiwan. Therefore, the acid-extracted industrial sludge is still an important source of hazardous waste. Usually, hazardous waste in Taiwan must be solidified and passed through the TCLP test before it is disposed in a landfill. The aim of this study is to develop a microwave process to stabilize copper ions in the sludge to replace the use of traditional solidification. In this study, two parameters - the reaction time of the microwave process and the additive reagents - were considered. The efficiency of stabilization of the microwave process was evaluated from the result of the TCLP test. The results showed that the stabilization efficiency of copper ions obtained using a microwave process without any added reagent depends highly on the property of the original acid-extracted sludge. Under some conditions, the leaching concentrations were much lower than those of the raw sludge. In additive reagent systems, the results showed that iron powder promoted the stabilization of copper ions more than the other additives such as sodium carbonate and sodium silicate. The leaching concentration of copper ions decreased dramatically from 179.4 to 6.5 mg/L below in the iron additive system.