Recycling of metals from pretreated waste printed circuit boards effectively in stirred tank reactor by a moderately thermophilic culture

https://doi.org/10.1016/j.jbiosc.2016.12.017Get rights and content

Highlights

  • Moderately thermophiles were adapted in increasing PPCBs density causing improved tolerance and efficient copper recovery.

  • Community structure was relatively simple during bioleaching at high PPCBs density.

  • The treatment process combining shaking table separation with bioleaching would provide a feasible way for PCBs recycling.

To seek a feasible technique for processing waste printed circuit boards (PCBs), pretreatment of PCBs by table separation and further bioleached by moderate thermophiles in a stirred tank reactor were investigated. The shaking table separation, conducted after grinding and sieving of PCBs, produced two fractions: metal-rich parts (RPCBs), which is more suitable for pyrometallurgy process than untreated PCBs, and metal-poor parts (PPCBs) with only 8.83% metals was then bioleached by a mixed culture of moderate thermophiles effectively. After adaptation, the mixed culture could tolerate 80 g/L PPCBs. The bioleaching results showed that metals recovery was 85.23% Zn, 76.59% Cu and 70.16% Al in only 7 days. Trace Pb and Sn were detected in the leachate because of precipitating. The microorganism community structure was analyzed by amplified ribosomal DNA restriction analysis. Two moderately thermophilic bacteria species were identified as Leptospirillum ferriphilum and Acidithiobacillus caldus. Furthermore, uncultured Thermoplasmatales archaeon was also detected in the leaching system. It was also shown that moderate thermophiles revealed best bioleaching ability when compared with mesophiles and the mixture of mesophiles and moderate thermophiles. Finally, we designed a two-stage process model according to the present study to achieve semi-industrial waste PCBs recycling and economic feasibility analysis indicated that the process was profitable.

Section snippets

A brief procedure description for this study

The main experimental design is shown in Fig. 1. Firstly, powdered PCBs is divided to RPCBs and PPCBs by shaking table separation, and the former containing metal concentrates can be processed by pyrometallurgy directly. Then PPCBs as low-grade material will be bioleached to extract residual metals at a relatively high pulp density by adapted moderate thermophiles.

Pretreatment of PCBs by sharking table separation

The waste printed circuit mother boards were obtained from electronics shop in Changsha, China. No physical or mechanical separation

Pretreatment of PCBs by table separation

For the pretreatment of PCBs, table separator was used to separate the plastics and metals. After separation, most of the metals were concentrated to RPCBs, whereas still a few metals remained in PPCBs. The content of metals in each fraction is shown in Table 2. It can be seen that only 8.83% total metal remained in PPCBs, compared with RPCBs (80.17% total metal). Thus PPCBs is not suitable for pyrometallurgical process, but bioleaching seems to be a feasible way for recycling.

Adaptation of microorganisms in PPCBs

To improve the

Acknowledgments

This work was supported by the National Natural Science Foundation of China (NSFC) (Nos. 31470230 and 51320105006), the Planned Science and Technology Project of Hunan Province, China (No. 2013FJ4068), and Australia CSIRO OCE Science Leader Grant.

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