Abstract
Bearing in mind the metal rich composition of printed circuit boards (PCBs), this material represents a secondary source of valuable metals and offers an entrepreneurial opportunity in the metal sales market. Based on the ability of microorganisms to regenerate and produce the chemical oxidants that are responsible for metal leaching, bioleaching has become an efficient and affordable alternative to conventional metal recycling technologies, although further research is still necessary before industrial implementation. This study focuses on the recovery of metals contained in mobile phone PCBs through a combined process. Two different PCB pre-treatments were evaluated: grinding the whole piece and removing the epoxy cover from the piece without grinding. The benefit of A. ferrooxidans activity on the metal solubilization rate was analyzed. Additional chemical leaching assays were also conducted for comparison purposes and the reagents ferric iron (Fe3+) and sulfuric acid (H2SO4) were selected for these experiments. The copper extraction results obtained in Fe3+ experiments with and without bacteria (A. ferrooxidans) were similar after 260 h of operation, indicating the need for alternative strategies to ensure a controlled and continuous metal biodissolution rate. The contribution of H2SO4 to the leaching processes for copper and nickel was almost negligible during the first 50 h, and more significant thereafter. The recovered metals were precipitated from a synthetic solution simulating a real ferric leaching by adding sodium hydroxide (NaOH) and sodium sulfide (Na2S). The combination of both precipitants allowed an effective removal of metals from the leachate.
Highlights
Electrical and electronic equipment (EEE) includes all devices that require electric currents or electromagnetic fields in order to function properly, as well as units that generate, transmit and measure the aforementioned currents and fields
The solids generated in the biotic and abiotic leaching solutions were identified by the XRD patterns that were obtained using a PANalytical Xpert PRO diffractometer (Malvern Panalytical, Leioa, Spain) with theta-theta configuration
printed circuit boards (PCBs) sample pulverization has been traditionally proposed as a prerequisite for improving the efficiency of metal bioleaching [27,35,36], and, only recently, several authors have incorporated the use of entire PCB pieces for this process [37,38]
Summary
Electrical and electronic equipment (EEE) includes all devices that require electric currents or electromagnetic fields in order to function properly, as well as units that generate, transmit and measure the aforementioned currents and fields. The group whose widespread use across the globe has led to an exponential growth in recent decades is that of small information technology and telecommunication equipment. This group includes gadgets, such as mobile phones (smartphones, phablets, etc.), GPS and navigation equipment, personal computers, printers or telephones. The amount of e-waste generated by their consumption has increased dramatically. In Spain alone, 32,726 t of e-waste were collected in 2018 (equivalent to 0.70 kg inhabitant−1 ), which was 8057 t more than in 2017 and represents an increase of 105% since 2009 [2]
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