Bioleaching of copper from waste printed circuit boards by bacteria-free cultural supernatant of iron\u2013sulfur-oxidizing bacteria

Weijin Wu,Minglong Zhu,Xiaocui Liu,Xu Zhang,Wensong Tan

doi:10.1186/s40643-018-0196-6

Weijin Wu, Minglong Zhu + Show 3 more

Open Access

https://doi.org/10.1186/s40643-018-0196-6

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Abstract

BackgroundThe toxicity of waste printed circuit boards (PCBs) to bacteria was considered as the major limitation in bioleaching of copper from PCBs. To reduce the toxicity of PCBs, copper extraction from PCBs was investigated using bacteria-free cultural supernatant from some metallurgical microbial consortium, whose predominant organisms were Leptospirillum ferriphilum and Sulfobacillus thermosulfidooxidans.ResultsAbout 100% copper was recovered in 2 h from 5 g/L PCBs by bacteria-free cultural supernatant. The result indicated that the indirect non-contact mechanism was the predominant mechanism in bioleaching of copper from PCBs. It was not necessary for bacteria to exist in copper extraction. In addition, the role of bacteria was most likely to regenerate Fe3+ as an oxidant. Furthermore, the biooxidation of Fe2+ to Fe3+ was determined as the rate-limited step in bioleaching of copper from PCBs. In addition, the biooxidation activity of bacteria would be strongly inhibited by the toxicity of PCBs.ConclusionThe separation of bacteria from the PCBs probably was the optimum way to avoid the negative effect of PCBs. Accordingly, a biooxidation–leaching–separation cycle was designed to avoid the toxicity of PCBs. Eventually, 93.4% of copper was recovered in total from 100 g/L PCB concentrates in 9 days.

Highlights

The toxicity of waste printed circuit boards (PCBs) to bacteria was considered as the major limitation in bioleaching of copper from PCBs
The purpose of the present study is to prove that if it is feasible to achieve the bioleaching of copper from PCBs using bacteria-free cultural supernatant
Almost 100% copper was dissolved by bacteria-free cultural supernatant when adding 5 g/L PCBs

Summary

Introduction

The toxicity of waste printed circuit boards (PCBs) to bacteria was considered as the major limitation in bioleaching of copper from PCBs. With the rapid development of electronic and electrical industries, more and more new electronic products are produced. When these electronic products reach their service life, a large number of e-wastes will be generated. It was estimated that about 20–25 million tons of e-waste were produced every year in the world (Robinson 2009). As the basic part of electronic equipment, PCBs have been increasing sharply with the increment of e-wastes. PCBs contained varieties of hazardous organic and inorganic substances which required special treatment to avoid environmental contamination (Robinson 2009).

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