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• An eco-friendly process is developed to enhance the bioleaching efficiency of metals. • Efficiency of metal bioleaching from WPCBs can be improved by mechanical activation. • Mechanical activation can induce a decrease in the particle size of WPCBs. • Mechanical activation can enhance the exposure of metals in WPCBs. • Activation of electrode potential of metals causes an increase of their bioleaching. The low bioleaching efficiency of Acidithiobacillus ferrooxidans results in its sparse industrial application for metal extraction from waste printed circuit boards (WPCBs). To improve the bioleaching efficiency of Acidithiobacillus ferrooxidans , we propose the use of mechanical activation to dispose WPCBs prior to performing bioleaching. Response surface methodology (RSM), scanning electron microscope- energy dispersive spectrometer (SEM-EDS), and laser particle size analyzer (LPSA) were used to optimize and analyze the mechanical activation process, respectively. The optimal conditions for mechanical activation was a milling time of 2 h, milling speed of 340 r min−1, and ball material ratio (w/w) of 10/1; the bioleaching rates of Cu, Ni, and Zn were 94.33%, 90.69%, and 90.78%, respectively. The bioleaching rates of Cu, Ni, and Zn were 74.75%, 70.46%, and 71.05%, respectively, without mechanical activation pretreatment. SEM-EDS and LPSA analyses indicated that mechanical activation could lead to a smaller particle size and expose wrapped metals, thus improving the bioleaching efficiency oyf tyhe metals inside the WPCBs. The electrode potential of the metals was likely changed by the mechanical activation, resulting in an improvement of their bioleaching efficiency. Additionally, the bioleaching rates of Pb, Cr, and Cd after mechanical activation pretreatment were 10.29%, 74.89%, and 54.12%, respectively. Contrastingly, the bioleaching rates of Pb, Cr, and Cd without mechanical activation pretreatment were 5.18%, 59.97%, and 37.12%, respectively. Thereinto, the precipitation of PbSO 4 may result in a decrease of leached Pb. We propose a mechanical activation process for improving the bioleaching efficiency of metals from WPCBs. [ABSTRACT FROM AUTHOR]

To improve the copper bioleaching efficiency from waste printed circuit board (WPCB) by Acidithiobacillus ferrooxidans ( A. ferrooxidans ), a novel simplified material (nitrogen-doped carbon nanotubes (NCNTs) modified electrode) was used in this paper. Experiments mainly including the exploration of NCNTs optimal concentration and recycling effect of NCNTs modified electrode were investigated. The variations of pH, ORP, Fe 2+ concentration and Cu 2+ concentration were studied in detail, and the mechanism of the modified electrode was also analyzed in this study. Conclusions were obtained that the optimal experimental conditions were: bacteria inoculation 10%, initial pH 2.0, WPCB powder 1 g, solid/liquid (w/v) ratio 1/50, temperature 28 °C, rotational speed 125 r/min and modified electrode 2.5 mg/cm 2 . The copper bioleaching rate reached 99% after 9 days reaction, and it was 20% higher than that of the group which was only added A. ferrooxidans. With the analysis of XRD, the precipitate formed (NH 4 )Fe 3 (SO 4 ) 2 (OH) 6 at the end of the reaction, and the modified electrode didn’t affect the formation of the yellow precipitate. Meanwhile, the modified electrode could be recycled, and the positive effect wasn’t weakened obviously on these processes. The results may provide a reference for enhancing the copper bioleaching efficiency from WPCBs and expand the application of NCNTs in hydrometallurgy field. [ABSTRACT FROM AUTHOR]

Exploration of enhancing bioleaching percent of copper from waste printed circuit board (WPCB) has received an increasing attention in recent years. This research explored the catalytic effect of graphene in bioleaching copper from WPCB by Acidithiobacillus ferrooxidans ( A. ferrooxidans ). Series of experiments were investigated, such as compatibility test between A. ferrooxidans and graphene, optimal dosage test of graphene, test of orthogonal experiment design, mechanism analysis of graphene, and recycling experiment of used graphene. Conclusions were obtained that graphene had a good compatibility with A. ferrooxidans , and it could catalyze the bioleaching reaction when added with appropriate dosage of graphene. The optimal dosage of graphene was 0.04 g in 50 ml culture solution, and 84% of copper was leached after five days bioleaching, while only 74% of copper was leached without adding graphene. The optimal condition of bioleaching copper was WPCB 10 g L − 1 , initial pH 2.5, bacterial activation time 4 days, and FeSO 4 ·7H 2 O 40 g L − 1 , about 91.8% of copper was leached. The mechanism analysis of graphene indicated that the transformation between Fe 2 + and Fe 3 + was actuated by A. ferrooxidans and graphene in these reactions, and both of FeCl 3 ·6H 2 O and KFe(SO 4 ) 2 (OH) 6 were generated in bioleaching process. The catalytic ability of bioleaching copper wasn't weakened by treating with 40% HNO 3 , and graphene could recycle and reuse in these reactions. Our experimental results shows that the catalysis of graphene in bioleaching copper from WPCB by A. ferrooxidans is promising. [ABSTRACT FROM AUTHOR]

• P. chrysosporium can leach copper from the copper-clad laminate. • P. chrysosporium can promote the leaching of copper by the change of electrochemical behavior. • P. chrysosporium leach copper as a result of EET-MIC and M−MIC. The leaching and electrochemical oxidation of the copper-clad laminate for manufacturing printed circuit boards were investigated in systems with and without the fungus P. chrysosporium , which yielded the copper-leaching efficiencies of 54% and 7.0%, respectively. In particular, the formation of a biofilm on the electrode surface reduced the open-circuit potential and increased the corrosion level, and the degree of increase and the rate of change of the current density in the fungal leaching system were higher than those of the sterile system. In addition, the cyclic voltammetry curves showed oxidation peaks that correspond to the oxidation of Cu to Cu2+. Further, for the fungal leaching system, the peak potential was highly negative and the curve area and peak current density were relatively high. Moreover, the electrochemical polarization parameters and the impedance characteristics were affected by the fungus, and the leaching systems were controlled by charge transfer and diffusion. In summary, P. chrysosporium can accelerate the leaching of copper as a result of the formation of extracellular electron transfer-induced microbiologically influenced corrosion (EET-MIC) and metabolite-induced microbiologically influenced corrosion (M−MIC). The enzymes and organic acids, which act as fungal metabolites, participate in the leaching of copper. [ABSTRACT FROM AUTHOR]

Abstract: Bioleaching processes were used to mobilize metals from printed wire boards (PWBs). The bacteria Acidithiobacillus ferrooxidans (A. ferrooxidans) and Acidithiobacillus thiooxidans (A. thiooxidans) isolated from an acidic mine drainage were grown and acclimated in presence of PWBs and then used as bioleaching bacteria to solubilize metals from PWBs. The experimental results demonstrate that all the percentages of copper, lead, zinc solubilized into the leaching solution from actual PWBs basically increased with decrease of sieve fraction of sample and decrease of PWBs concentration. The concentration of PWBs should be controlled under the range from 7.8 to 19.5gl−1. Under 7.8gl−1 of the concentration of PWBs, the percentages of copper solubilized are 99.0%, 74.9%, 99.9% at 0.5–1.0mm of sieve fraction at 9d of leaching time by the pure culture of A. ferrooxidans, the pure culture of A. thiooxidans, and mixed culture of A. ferrooxidans and A. thiooxidans, respectively, while the percentages of copper, lead and zinc solubilized are all more than 88.9% at <0.35mm of the sieve fractions of sample at 5d of leaching time by the above three kinds of cultures. Variation of pH and redox potential of leaching solution with time implied that Fe3+ oxidized from Fe2+ in the culture medium in presence of A. ferrooxidans caused the mobilization of metals. It is concluded that A. ferrooxidans and A. thiooxidans were able to grow in the presence of PWBs and the pure culture of A. ferrooxidans, and the mixed culture of A. ferrooxidans and A. thiooxidans can not only efficiently bioleach the main metal copper but also bioleach other minor metals such as lead, zinc as well. [Copyright &y& Elsevier]