Gold Bioleaching of Electronic Waste by Cyanogenic Bacteria and its Enhancement with Bio-Oxidation
TL;DR: Bioleaching the biooxidised e-waste significantly improved gold recovery, especially by C. violaceum, particularly at high pulp density, and the ratio of gold/copper in leachates after bioleaching of theBiooxidized e-Waste was also found to be increased.
Abstract: This work compares gold bioleaching from e-waste containing gold and copper by Chromobacterium violaceum and Pseudomonas fluorescens. The effect of pulp density (ranging from 0.5 to 8%w/v) was examined. Although C. violaceum produced more cyanide than P. fluorescens in the absence of e-waste, P. fluorescens showed higher growth rate, cyanide production and gold leaching efficiency at all pulp densities. Pretreatment with biooxidation of the e-waste using Acidithiobacillus ferrooxidans resulted in the removal in excess of 80% of the copper present in the waste, and increased the gold/copper ratio in the residual solid. Bioleaching the biooxidised e-waste significantly improved gold recovery, especially by C. violaceum, particularly at high pulp density. For example, at pulp densities of 2 and 4% w/v, gold recovery from non-biooxidzed e-waste was 0.22 and 0.14% respectively. Higher gold recovery, at 8%, was obtained for bioleaching of the biooxidised e-waste at both these pulp densities. The ratio of gold/copper in leachates after bioleaching of the biooxidized e-waste was also found to be increased.
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TL;DR: The current review addresses the individual issues related to chemical and biological extraction techniques and proposes a hybrid-methodology which incorporates both, along with safer chemicals and compatible microbes for better and efficient extraction of metals from the E-waste.
264 citations
Additional excerpts
...Pham and Ting (2009) extracted Au from E-waste by utilizing cynogenic-bacteria (Chromobacterium violaceum and Pseudomonas fluorescens) along with a pretreatment for bio-oxidation of E-waste by A. ferrooxidans (which specifically remove Cu leaving Au residues behind)....
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TL;DR: This study provided a proof-of-concept of a two-step approach in metal bioleaching from PCB, by bacterially produced lixiviants, by chemolithotrophic acidophilic Acidithiobacillus ferrivorans and A. thiooxidans.
177 citations
TL;DR: A review of the role of microorganisms in gold processing and recovery can be found in this paper, which covers aspects such as the biotechnical pre-treatment of gold ores and concentrates, microbially catalysed permeability enhancement of ore bodies, gold solubilisation through biooxidation and complexation with biogenic lixiviants, and micro-bially mediated gold recovery and loss from leach liquors.
125 citations
TL;DR: Results showed that gold bioleaching efficiency from electronic scrap was enhanced under alkaline conditions with mutated bacteria compared toBioleaching at physiological pH (around 7) of C. violaceum.
110 citations
Cites background from "Gold Bioleaching of Electronic Wast..."
...…gold per ton (Korte et al., 2000; Pham and Ting, 2009), electronic scrap material (ESM) has significantly higher gold content at around 10–10,000 grams gold per ton (Cui and Zhang, 2008; Pham and Ting, 2009), making it a viable alternative and more economic source of gold compared to natural ores....
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...Compared with natural gold ores which has around 0.5–13.5 g gold per ton (Korte et al., 2000; Pham and Ting, 2009), electronic scrap material (ESM) has significantly higher gold content at around 10–10,000 grams gold per ton (Cui and Zhang, 2008; Pham and Ting, 2009), making it a viable alternative…...
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TL;DR: The construction of a metabolically-engineered strain of Chromobacterium violaceum that produces more (70%) cyanide lixiviant and recovers more than twice as much gold from electronic waste compared to wild-type bacteria is shown.
Abstract: Conventional leaching (extraction) methods for gold recovery from electronic waste involve the use of strong acids and pose considerable threat to the environment. The alternative use of bioleaching microbes for gold recovery is non-pollutive and relies on the secretion of a lixiviant or (bio)chemical such as cyanide for extraction of gold from electronic waste. However, widespread industrial use of bioleaching microbes has been constrained by the limited cyanogenic capabilities of lixiviant-producing microorganisms such as Chromobacterium violaceum. Here we show the construction of a metabolically-engineered strain of Chromobacterium violaceum that produces more (70%) cyanide lixiviant and recovers more than twice as much gold from electronic waste compared to wild-type bacteria. Comparative proteome analyses suggested the possibility of further enhancement in cyanogenesis through subsequent metabolic engineering. Our results demonstrated the utility of lixiviant metabolic engineering in the construction of enhanced bioleaching microbes for the bioleaching of precious metals from electronic waste.
91 citations
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TL;DR: In the detailed literature survey, value distributions for different electronic waste samples were calculated, and it was showed that the major economic driver for recycling of electronic waste is from the recovery of precious metals.
1,391 citations
TL;DR: In this article, the formation of inorganic and organic acids caused the mobilization of metals from electronic waste materials, and a two-step leaching process was proposed where biomass growth is separated from metal leaching.
389 citations
TL;DR: This chapter focuses on cyanide metabolism in micro-organisms, which is probably the simplest secondary metabolic system and a continued investigation of cyanide formation should greatly aid a better understanding of microbial secondary metabolism.
Abstract: Publisher Summary This chapter focuses on cyanide metabolism in micro-organisms. It is noted that cyanide is a relatively common product of microbial as well as plant metabolism. Cyanide production by micro-organisms has many characteristics typical of secondary metabolism. In addition, it is probably the simplest secondary metabolic system and a continued investigation of cyanide formation should greatly aid a better understanding of microbial secondary metabolism. Cyanide degradation by Chromobacterium violaceum, or C. violaceum, is known to synthesize at least three enzymes capable of metabolizing cyanide. These include rhodanese, γ-cyano-α-aminobutyric acid synthase, and β-cyanoalanine synthase. The concentrations of all three enzymes increase in the post-cyanogenic period. The buildup of β-cyanoalanine is particularly noteworthy in bacteria grown under conditions of high cyanogenesis. The suspensions of harvested C. violaceum cells are also able to form β-cyanoalanine when incubated with cyanide and serine.
212 citations
TL;DR: The findings demonstrate for the first time the microbial mobilization of metals other than gold from solid materials and represent a novel type of microbial metal mobilization based on the ability of certain microbes to form HCN.
197 citations
TL;DR: Cyanogenic Chromobacterium violaceum, Pseudomonas fluorescens, and P plecoglossicida were able to mobilize silver, gold, and platinum when grown in the presence of various metal-containing solids such as gold-containing electronic scrap, silver-containing jewelry waste, or======platinum-containing automobile catalytic converters as mentioned in this paper.
172 citations