Recovery of copper-contaminated sludge in a two-stage leaching process

The purpose of this study was to develop an effective method of processing copper-contaminated sludge, produced during the manufacture of printed circuit boards (PCBs). In the first stage, 2 N sulfuric acid was used to leach the wet sludge. A solid to liquid ratio of approximately 1:10 was used. Because hydroxide compounds in the sludge were not stable when exposed to acid, the copper extraction percentage exceeded 85% in 15 min. In the second stage, an ammonia solution was used to purify the sulfuric acid leachate by forming an ammine complex. During this process hydroxide compounds were formed by the impurities (Al3+, Fe2+, Pb2+, etc.) in the leachate atpH 10. After purification, the residual metallic hydroxide compounds were treated by the ferrite process to produce a stable oxide compound. The ammine solution was then heated to evaporate the ammonia, and copper hydroxide was formed in solution. The temperature was maintained at 80 degrees C by aeration. In the process, copper hydroxide was transformed into copper oxide. The copper concentration reached 98.4%. (c) 2005 American institute of Chemical Engineers.