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 at pH 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° C by aeration. In the process, copper hydroxide was transformed into copper oxide. The copper concentration reached 98.4%.