Journal of Hazardous Materials 184 (2010) 812–818 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat Bioleaching of copper from waste printed circuit boards by bacterial consortium enriched from acid mine drainage Yun Xiang a,b , Pingxiao Wu a,b,c , Nengwu Zhu a,b,c,∗ , Ting Zhang a,c , Wen Liu d , Jinhua Wu a,b,c , Ping Li a,b,c a College of Environmental Science and Engineering, South China University of Technology, Guangzhou 510006, China b The Key Laboratory of Pollution Control and Ecosystem Restoration in Industry Clusters of Ministry of Education, Guangzhou 510006, China c The Key Laboratory of Environmental Protection and Eco-Remediation of Guangdong Regular Higher Education Institutions, Guangzhou 510006, China d Department of Environmental Sciences, Rutgers University, New Brunswick, NJ 08901, United States article info Article history: Received 10 May 2010 Received in revised form 19 August 2010 Accepted 28 August 2010 Available online 24 September 2010 Keywords: Bioleaching Waste printed circuit boards Copper Acid mine drainage Bacterial consortium abstract The objectives of this study were to evaluate the solubility of copper in waste printed circuit boards (PCBs) by bacterial consortium enriched from natural acid mine drainage, and to determine optimum conditions of bioleaching copper from PCBs. The results indicated that the extraction of copper was mainly accomplished indirectly through oxidation by ferric ions generated from ferrous ion oxidation bacteria. The initial pH and Fe 2+ concentration played an important role in copper extraction and precipitate formation. The leaching rate of copper was generally higher at lower PCB powder dosage. Moreover, a two-step process was extremely necessary for bacterial growth and obtaining an appropriate Fe 2+ oxidation rate; a suitable time when 6.25 g/L of Fe 2+ remained in the solution was suggested for adding PCB powder. The maximum leaching rate of copper was achieved 95% after 5 days under the conditions of initial pH 1.5, 9 g/L of initial Fe 2+ , and 20 g/L of PCB powder. All findings demonstrated that copper could be efficiently solubilized from waste PCBs by using bacterial consortium, and the leaching period was shortened remarkably from about 12 days to 5 days. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Printed circuit boards (PCBs) are the basal and essential part of the electronic industry. It was estimated by the Ministry of Infor- mation Industry of the P.R. China that the total production of PCBs would reach more than 1.1 × 10 9 m 2 in 2010 and the global market share would be over 30%, which meant a dramatic increase of elec- tronic wastes [1]. With the rapid discard of electronic wastes, the quantity of waste PCBs will be tremendous. Traditional disposal methods of electronic wastes including incineration and landfills are not recommended due to environmental protection, human health consideration [2–4], and the recovery of valuable materials (e.g. metals, polymers and ceramics). Especially, metals contained in waste PCBs are of economical significance for recycling [5]. Com- paring to metal mines, the purity and amount of metals contained in waste PCBs are higher than those in rich-content minerals [6]. From this point of view, waste PCBs could be considered as an “artificial ore”. ∗ Corresponding author at: College of Environmental Science and Engineering, South China University of Technology, Guangzhou 510006, China. Tel.: +86 20 8711 2993; fax: +86 20 8711 2993. E-mail address: nwzhu@scut.edu.cn (N. Zhu). The existing technologies of recycling metals from waste PCBs are either pyrometallurgical or hydrometallurgical processing which generate second atmospheric pollution through the release of toxic gas, i.e. dioxins and furans, or high volume acid wastewater [7–10]. Besides, these processes are highly dependent on invest- ments and regarded as uneconomical ways to extract metals from waste PCBs. Thus, use of microorganisms for the recovery of metals from waste PCBs could be an economical alternative. Bioleaching has been applied successfully and commercially in biohydrometallurgy for extracting copper and precious met- als from low-grade ores and tailings for many years [11–13]. It is believed to be one of the most promising technologies without too much capital investment, labor need, and energy consumption [14,15]. In recent years, more researches have been carried out on the bioleaching of metals from various samples, such as sludge, fly ashes, sediments, soils, batteries, etc. [16–25]. Even, electronic scraps and waste PCBs have also been considered to recover metals through bioleaching [26–31]. Previous studies were mostly conducted with two Acidithiobacil- lus species, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans, the most widely used species in bioleaching process. But recently, the synergistic effect during the bioleaching process has been noticed via mixed bacterial leaching. It was considered that the acidophilic heterotrophs could promote the growth of the mineral oxidizers by consuming organic excretion produced 0304-3894/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2010.08.113