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标题:Gold biorecovery from e-waste: An improved strategy through spent medium leaching with pH modification.
时间:2019-12-03 09:36:13
DOI:10.1016/j.chemosphere.2015.05.046
PMID:26025187
作者:Natarajan, Gayathri; Ting, Yen-Peng
关键词:Bioleaching;Chromobacterium violaceum;Gold;Spent medium;Electronic waste;
出版源: 《Chemosphere》 ,136 :232-238
摘要:Highlights • Pure culture of C. violaceum shows highest cyanide production and gold recovery. • pH decreases at higher pulp densities due to toxicity of ESM on bacterial growth. • As pulp density increases, gold and copper bioleaching efficiency decreases. • Spent medium leaching shows higher gold recovery than two-step bioleaching. • Higher pH of spent medium increases cyanide ion availability for gold complexation. Abstract Rapid technological advancement and relatively short life time of electronic goods have resulted in an alarming growth rate of electronic waste which often contains significant quantities of toxic and precious metals. Compared to conventional recovery methods, bioleaching is an environmentally friendly process for metal extraction. Gold was bioleached from electronic scrap materials (ESM) via gold–cyanide complexation using cyanide produced from pure and mixed cultures of cyanogenic bacteria Chromobacterium violaceum, Pseudomonas aeruginosa and Pseudomonas fluorescens. As ESM was toxic to the bacteria, a two-step bioleaching approach was adopted where the solid waste was added to the bacterial culture after it has reached maximum growth and cyanide production during early stationary phase. Pure culture of C. violaceum showed the highest cyanide production, yielding maximum gold recovery of 11.3% at 0.5% w/v pulp density of ESM in two-step bioleaching. At the same pulp density of ESM, spent medium bioleaching using bacterial cell-free metabolites achieved gold recovery of 18%. Recovery increased to 30% when the pH of the spent medium was increased to shift the equilibrium in favor of cyanide ions production. It is demonstrated for the first time that pH modification of spent medium further improved metal solubilization and yielded higher metal recovery (compared to two-step bioleaching).
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目录:
  • Gold biorecovery from e-waste: An improved strategy through spent medium leaching with pH modification
    • 1 Introduction
    • 2 Materials and methods
      • 2.1 Electronic scrap material
      • 2.2 Bacteria
      • 2.3 Acid digestion of ESM and cells
      • 2.4 Pretreatment of ESM
      • 2.5 Free cyanide analysis
      • 2.6 Bioleaching experiments
      • 2.7 Transmission electron microscopy (TEM)
    • 3 Results and discussion
      • 3.1 Free cyanide production and two-step gold bioleaching (0.5% w/v pulp density) of pure and mixed culture of cyanogenic bacteria
      • 3.2 pH profile of C. violaceum in two-step bioleaching
      • 3.3 Metal recovery in two-step and spent medium bioleaching with pretreated ESM
      • 3.4 Gold recovery with alkaline spent medium
    • 4 Conclusion
    • Acknowledgements
    • Appendix A Supplementary material
    • References

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