An engineered bioplatform utilizing the purple pigmented bacterium Chromobacterium violaceum for sustainable gold extraction from refractory ores and electronic waste through biological cyanide production (biocyanidation). This system represents an environmentally-friendly alternative to conventional chemical cyanide leaching, producing controlled amounts of biogenic cyanide that complexes gold as soluble Au(CN)₂⁻ while simultaneously metabolizing excess cyanide to prevent environmental toxicity. C. violaceum is a versatile heterotrophic bacterium that produces the purple pigment violacein and synthesizes cyanide through hydrogen cyanide (HCN) biosynthesis pathways. The bacterium is pre-grown in nutrient medium to stationary phase, then activated for cyanide production upon exposure to ground refractory gold ores or electronic scrap (PCBs, connectors). Operating at near-neutral pH (6.5-7.5) and mesophilic temperature (28-32°C), the system achieves gold extraction efficiencies comparable to chemical cyanidation (70-85% recovery) from refractory sulfide ores and precious metal-bearing e-waste. The process requires ore grinding pretreatment to liberate gold particles and operates in aerated bioreactors with glycerol or glucose as carbon source. Biocyanidation kinetics are slower than chemical leaching (7-14 days vs. 24-48 hours) but offer significant advantages: lower cyanide concentrations (50-200 ppm vs. 500-2000 ppm), ambient temperature operation, biological cyanide detoxification, and reduced environmental liability. The platform enables decentralized gold recovery from low-grade ores and artisanal mining operations while avoiding hazardous chemical transport. Gold is recovered from pregnant leach solution by activated carbon adsorption followed by elution and electrowinning or zinc cementation.
Taxonomy
| Taxon | Ontology ID | Functional Roles | Abundance |
|---|---|---|---|
| Chromobacterium violaceum | NCBITaxon:536 |
PRIMARY_PRODUCER
PRIMARY_DEGRADER
|
DOMINANT |
Ecological Interactions
Biogenic Cyanide Production from Glycine
COMMENSALISMSource Taxon: Chromobacterium violaceum
Metabolites: glycine (CHEBI:15428), hydrogen cyanide (CHEBI:18407), cyanide (CHEBI:17514), glycerol (CHEBI:17754), D-glucose (CHEBI:17634)
Biological Processes:
- hydrogen cyanide biosynthetic process (GO:0042402)
- glycine metabolic process (GO:0006544)
Evidence
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doi:10.1016/j.mineng.2013.03.022 - SUPPORT (IN_VITRO)"Chromobacterium violaceum produces and detoxifies small amounts of cyanide from simple carbon sources"
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doi:10.1016/j.mineng.2013.03.022 - SUPPORT (IN_VITRO)"The bacteria were pre-grown to stationary phase before being activated by the addition of refractory ore"
Gold Cyanide Complexation and Dissolution
MUTUALISMMetabolites: cyanide (CHEBI:17514), gold atom (CHEBI:29287), dicyanoaurate(1-) (CHEBI:30319), dioxygen (CHEBI:15379), arsenopyrite (CHEBI:134121), pyrite (CHEBI:46727)
Biological Processes:
- oxidation-reduction process (GO:0055114)
Evidence
-
doi:10.1016/j.mineng.2013.03.022 - SUPPORT (IN_VITRO)"Chromobacterium violaceum can be used for the recovery of gold from refractory ores"
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doi:10.1007/s10163-014-0276-4 - SUPPORT (IN_VITRO)"Biocyanidation of gold from electronic scrap by Chromobacterium violaceum"
Biological Cyanide Detoxification
COMMENSALISMSource Taxon: Chromobacterium violaceum
Metabolites: hydrogen cyanide (CHEBI:18407), formamide (CHEBI:16397), formic acid (CHEBI:30751), ammonia (CHEBI:16134), carbon dioxide (CHEBI:16526)
Biological Processes:
- cyanide catabolic process (GO:0009437)
- response to toxic substance (GO:0009636)
Evidence
-
doi:10.1016/j.mineng.2013.03.022 - SUPPORT (IN_VITRO)"Chromobacterium violaceum produces and detoxifies small amounts of cyanide"
Ore Pretreatment and Particle Size Effects
COMPETITIONMetabolites: arsenopyrite (CHEBI:134121), pyrite (CHEBI:46727)
Biological Processes:
- response to metal ion (GO:0010038)
Evidence
-
doi:10.1016/j.mineng.2013.03.022 - SUPPORT (IN_VITRO)"refractory ore requires grinding pretreatment to liberate gold particles"
Environmental Factors
| Factor | Value | Unit |
|---|---|---|
| pH | 6.5-7.5 | pH units |
| Temperature | 28-32 | °C |
| Biocyanide Concentration | 50-200 | ppm CN⁻ |
| Leaching Time | 7-14 | days |
| Gold Extraction Efficiency | 70-85 | % recovery |
| Ore Pulp Density | 5-15 | % w/v |
| Particle Size (Ore Grinding) | 200-400 | mesh (37-74 μm) |
| Carbon Source for Bacterial Growth | Glycerol or glucose | qualitative |
| Oxygen Requirement | Aerobic with aeration | qualitative |
| Pre-growth and Activation Protocol | Stationary phase pre-growth | qualitative |
| Substrate Ore Types | Refractory arsenopyrite, pyrite, carbonaceous sulfides | qualitative |