Fig. 8From: Bioleaching of copper from waste printed circuit boards by bacteria-free cultural supernatant of iron–sulfur-oxidizing bacteriaInfluence of the increase of the numbers of cycles on biooxidation process: the variation of Fe3+ concentration (a) and Fe2+ concentration (b). The arrows mean the supernatants were removed and mediums after a cycle were returned. In addition, the concentration of copper (c) recovered every dayBack to article page