A Green and Sustainable Process for the Recovery of Gold from Low-Grade Sources Using Biogenic Cyanide Generated by Bacillus megaterium: A Comprehensive Study

Abstract

The decreasing grade of gold deposits and environmental regulations concerning the use of cyanide, a conventional extraction agent used in gold recovery, has highlighted the challenge in the field of gold extraction. The bioleaching of gold using microorganisms for in situ cyanide production to recover gold is a promising new approach for prohibiting the use of conventional chemical cyanide. For the first time, this study reports a comprehensive investigation on the role of pH on individual steps of Bacillus megaterium bacterial growth, cyanide production, and gold recovery. This novel way of maximizing biogenic cyanide is highly efficient and demonstrates biocyanidation as a potentially viable technique for direct treatment of sulfidic gold ores, i.e., eliminating the step of biooxidation for the first time. The low-grade sources were treated with both chemical cyanide and biogenic cyanide generated by B. megaterium. Results indicate that the bacteria generated a maximum of 61.89 ppm cyanide, which correspondingly recovered over 87% and 43% gold from O1 and O2 sources, respectively, comparable to gold recoveries by chemical leaching. The pure gold powder leaching was also performed to evaluate the loss in gold recovery due to the biosorption of gold to bacterial cells. The feasibility of the work is also supported by green chemistry metrics, and a comparison has been made between conventional and biocyanide leaching. The results revealed the potential of biocyanidation for industrial applications.

Application of Biogenic Thiosulfate Produced by Methylophaga sulfidovorans for Sustainable Gold Extraction

“…Gold extraction efficiency in ore leaching experiments was calculated indirectly using fire assay results from the feed material and residue of each experiment (eq ) …”

“…Bioleaching gold using amino acids, organic acids, cyanide, and iodine produced by bacteria has been reported in the literature . Research for gold and platinum group metal leaching with biogenic cyanide has been investigated by several authors. − However, biogenic cyanide still has many of the drawbacks of cyanidation such as toxicity, the primary benefit being potential for on-site production. Amino acids and proteins were reported to increase gold dissolution in thiosulfate solutions by complexing with copper to reduce the consumption of thiosulfate from interactions with copper. , Biogenic thiosulfate produced by sulfate-reducing bacteria in organic carbon-deficient soils has been proposed as a cause for gold mobilization in subsurface environments …”

Selective Extraction and Recovery of Gold from Complex Thiosulfate Pregnant Leach Liquor Using Cyphos IL 101

“…The risks and costs associated with the operation of hazardous cyanide, the precautions for safe handling/transportation of cyanide, and the necessity for remediating the residues and leachates after the process are some of the main drawbacks. 3 In addition, as a consequence of the preg-robbing phenomenon (gold-cyanide compound is adsorbed to the organic part of the residue and is not recovered), the cyanidation process cannot deliver high leaching efficiencies for the feed with the carbonaceous matter, because of the loss of gold. 4 Alternatively, thiosulfate is the second-best reagent for commercial treatment of gold, because it is efficient, nonhazardous, does not show preg-robbing behavior in treating the resources containing carbonaceous matter, and has been used by Barrick Gold Corporation in the Goldstrike Mine.…”

Novel Extraction Process for Gold Recovery from Thiosulfate Solution Using Phosphonium Ionic Liquids

“…Gold, a noble and precious metal has been extensively used in jewelry, electronics, aerospace, dentistry, orthopedics, etc. 1 The conventional gold extraction process from primary and secondary resources applies sodium cyanide as the most promising gold leaching lixiviant. The extreme toxicity of cyanide results in harmful environmental impacts.…”