Development of a Sustainable Alternative for the Ammoniacal Cyanidation of Copper–Gold Ores Through a Biological Approach

Due to the problems arising from the presence of copper in the gold cyanidation process, including high cyanide consumption and occupation of the activated carbon surface, biological ammoniacal cyanidation was implemented as a resolution. Bacillus megaterium was implemented to produce cyanide and ammonia in nutrient broth and vinasse media. Maximum cyanide concentrations of 29.8 and 47.5 mg/L were produced using 3 g/L glycine in the mentioned media, respectively. Afterward, the Box-Behnken experiment design method was implemented to optimize ammonia biogenesis in vinasse culture, where 1974 mg/L ammonia was synthesized at 13.56 g/L calcium chloride, 7.2 g/L urea, and pH = 7.9. Three different strategies, namely: (1) bio-cyanidation, (2) bio-ammoniacal cyanidation, and (3) bio-ammonia pretreatment/bio-cyanidation, were employed to recover gold and copper from a 1% solid pulp. Afterward, using the nutrient broth medium, 49% gold was recovered by the first approach; the second approach extracted 9.2% gold and 33.5% copper, and 77% copper removal and 76% gold recovery were achieved through the third technique. Nutrient broth substitution with vinasse increased the gold recovery to 97% in the third approach. Hence, ammoniacal pretreatment, in combination with bio-cyanidation, is suggested to recover gold from copper–gold ores. In conclusion, the originality of the present work lies first in developing a bacterial culture procedure in which nutrient broth was replaced with vinasse as an industrial byproduct to make the process more eco-friendly. And secondly, in using the biogenic ammonia to leach out copper from the copper–gold ore and prepare it for gold biocyanidation.