Feasibility study of technical treatment plant for the recovery of valuable material from aluminum-contaminated sludge

The purpose of this pilot plant study was to provide the method which could be utilized to recover copper and coagulant from aluminum-contaminated sludge by alkaline leaching. Alkaline reagent was mixed with the sludge, and the optimized conditions were as followed: reaction temperature of 70°C; reaction volume of 1,500L; stirring rate of 200 rpm and air flow rate of 5 L air/min per liter suspension volume. When the pH value remained stable, the reaction was terminated followed by solid-liquid separation. The leaching rate of Al from sludge was about 90% and the Cu content in solid residue was roughly 97%. The weight reduction of the sludge was nearly 24%. By this treatment method, not only the waste reduction of aluminum-contaminated sludge can be achieved, but also the copper can be concentrated in solid for the further pyrometallurgical treatment. The great amount of obtained alkaline and coagulant reagents can be reused as neutralizer and coagulant in wastewater treatment to reduce the treatment cost. The preliminary economical evaluation of this process with a capacity of 8 tons copper containing sludge per day in the united wastewater treatment plant was discussed. Moreover, some economically significant parameters such as construction, operating and maintenance were considered. Therefore, the capital cost would be 0.200 million US$. Annual operating and maintenance cost would be about 0.153 million US$. Annual net profit would be about 0.447 million US$. Hence, the total investment which was utilized in alkaline leaching test could be paid back in the time period of 6 months.