Consideration of Influential Factors on Bioleaching of Gold Ore Using Iodide-Oxidizing Bacteria

Abstract

Iodide-oxidizing bacteria (IOB) oxidize iodide into iodine and triiodide which can be utilized for gold dissolution. IOB can be therefore useful for gold leaching. This study examined the impact of incubation conditions such as concentration of the nutrient and iodide, initial bacterial cell number, incubation temperature, and shaking condition on the performance of the gold dissolution through the experiments incubating IOB in the culture medium containing the marine broth, potassium iodide and gold ore. The minimum necessary concentration of marine broth and potassium iodide for the complete gold dissolution were determined to be 18.7 g/L and 10.9 g/L respectively. The initial bacterial cell number had no effect on gold dissolution when it was 1 × 104 cells/mL or higher. Gold leaching with IOB should be operated under a temperature range of 30–35 °C, which was the optimal temperature range for IOB. The bacterial growth rate under shaking conditions was three times faster than that under static conditions. Shaking incubation effectively shortened the contact time compared to the static incubation. According to the pH and redox potential of the culture solution, the stable gold complex in the culture solution of this study could be designated as gold (I) diiodide.

Bioleaching of Gold from Sulfidic Gold Ore Concentrate and Electronic Waste by Roseovarius tolerans and Roseovarius mucosus

“…A comparison of maximum bioleaching yields achieved in this study and selected previous studies is shown in Table 7 . The maximum gold yield detected for R. tolerans with gold concentrate in this study was similar to that reported by Khaing et al [ 14 , 21 ] for other R. tolerans strains leaching sulfide ore. However, the maximum yield obtained with R. mucosus for ore concentrate was lower than that previously reported for strains of Roseovarius genus.…”

“…The application of IOB for bioleaching gold has been previously proposed as a sustainable alternative to cyanide [ 10 ] and, the use of IOB isolated from iodide-rich brine waters has been explored for leaching gold from gold-containing ore [ 14 , 21 ]. This study evaluated the ability of IOB sourced from a commercial culture collection, R. tolerans DSM 11457 T and R. mucosus DSM 17069 T , to bioleach gold from e-waste and sulfidic gold ore concentrate.…”

“…R. tolerans DSM 11457 T was originally isolated from a hypersaline lake in East Antarctica [ 27 ] whereas R. mucosus DSM 17069 T was isolated from a marine dinoflagellate [ 28 ]. Neither of the strains was described as an IOB in the original species descriptions, but were selected for this study based on other reports on the members of Roseovarius genus being able to oxidize iodide [ 14 , 18 , 21 ]. While previous studies have evaluated the use of strains of Roseovarius genus to leach gold from ore using one-step leaching, this study explored gold bioleaching with R. tolerans DSM 11457 T and R. mucosus DSM 17069 T from gold ore concentrate and e-waste using one-step, two-step and spent medium bioleaching.…”

“…On the contrary, Khaing et al [ 14 ] reported the cell numbers of a strain from Roseovarius genus to increase from 3 × 10 6 cell·mL −1 to 5 × 10 8 cell·mL −1 during the bioleaching of gold from sulfide ore. In another study, Khaing et al [ 21 ] reported that initial cell numbers of IOB had no effect on gold dissolution from sulfide ore when the initial cell numbers were 1 × 10 4 cell·mL −1 to 1 × 10 6 cell·mL −1 and during the 10-day incubation the cell numbers increased from 1 × 10 4 cell·mL −1 to 4.2 × 10 7 cell·mL −1 . Therefore, the initial cell numbers used in the present study were likely not the limiting factor in the gold bioleaching, but some toxic components of the ore concentrate and e-waste used for bioleaching may have inhibited bacterial growth [ 30 ].…”

“…Another strain, Roseovarius ( R .) sp., can oxidise I − to I 2 with oxygen as the electron acceptor (Reaction 2) [ 18 , 19 , 20 , 21 ]: 4I − + O 2 + 4H + → 2I 2 + 2H 2 O …”