Identification of microorganisms at different times in a bioleaching process for the recovery of gold and silver from minerals in oxide form

In this study, gold and silver were recovered through a bioleaching process conducted at room temperature over 11 days. Native bacteria and varying ratios of mineral pulp to culture medium (20/80, 37.5/62.5, and 50/50 %) from a mining operation in Zacatecas, Mexico, were evaluated. The mineral was crushed to a particle size of 0.125 inches or smaller, containing gold and silver concentrations of 0.609 g/ton and 138.89 g/ton, respectively. Four native microorganisms were identified using molecular biology techniques and a 16S rRNA gene fragment: <i>Acidovorax citrulli</i>, <i>Brevundimonas albigilva</i>, <i>Sphingomonas korenensis</i>, and <i>Methylobacterium organophilum</i>. The bioleaching system achieved metal extractions of 84.12 % and 63.93 % for gold and silver, respectively. Different microorganisms were identified at various processing times: <i>Sphingomonas korenensis</i> (days 1, 2, 5, 8, and 11), <i>Methylobacterium organophilum</i> (days 1 and 2), <i>Paenibacillus dongdonensis</i> (days 1 and 2), <i>Brevundimonas albigilva</i> (day 5), <i>Ureibacillus manganicus</i> (day 5), <i>Peribacillus simplex</i> (day 8), <i>Niallia circulans</i> (day 8), <i>Massilia atriviolacea</i> (day 11), and <i>Bacillus licheniformis</i> (day 11). The dominant bacterium throughout the process was <i>Sphingomonas korenensis</i>, which appeared at all stages of the experiment.