Importance of Soybean Meal and Ozone in the Extraction of Gold from Silicate Ore

In this research, the recovery of gold from silicate ore using amino acids derived from soybean meal was evaluated. The results indicated that soybean meal needed to be hydrolyzed by 4 M hydrochloric acid before using in the extraction of gold to increase the concentrations of soluble amino acids. Approximately 34% of gold was leached using a 1:5 (w/v) soybean meal hydrolysate within 3 h. Furthermore, 81% gold leachability was obtained by two leaching batches (57% and 24% from the first and the second leaching, respectively) using a fresh 1:5 (w/v) soybean meal hydrolysate supplemented with 167 mg L⁻¹ aqueous ozone (Ozonation time = 10 min) at 4% pulp density, a lixiviant with an initial pH of 7.00 and incubated for 3 h per batch due to the combined actions of amino acids and ozone. The ozone and the hydroxyl radical act as strong oxidizers. In addition, amino acids present in soybean meal hydrolysate serve as ligands to bind with soluble gold to form gold-amino complexes to prevent the precipitation of gold. This novel lixiviant for the sustainable gold extraction can be developed and utilized as an environmentally friendly, safe, and low-cost for hydrometallurgy in the future.