Mercury Removal from Glycine Leach Solutions Using Sodium Sulfide (Na2S) Precipitation

Amino acid leaching has been considered an environmentally friendly alternative for gold recovery; however, the dissolution of mercury (Hg) during the leaching of amalgamation tailings remains a major challenge. This study is a novelty study that focuses on Hg removal by passing the Hg-containing tailings, previously processed by amalgamation, into solution via glycine (NH2CH2COOH) leaching. In this regard, a precipitation method using sodium sulfide (Na₂S) was developed to remove Hg from solutions obtained after glycine leaching. The effects of precipitation time, pH, Na2S dosage, and temperature were investigated. The effects of pH, precipitation time, and temperature were found to be limited within the investigated ranges. The results showed that Na₂S dosage was the most effective parameter in mercury removal. The initial Hg concentration of 12,160 ppb was reduced to 223 ppb at a Na₂S:Hg molar ratio of 60, corresponding to approximately 98% removal efficiency under the selected operating conditions. Increasing the Na₂S:Hg ratio to 80 resulted in a slightly higher removal efficiency (~99%) with a final Hg concentration of 144 ppb; however, a ratio of 60 was considered optimal in terms of reagent consumption and process efficiency. The outcomes indicate that Hg removal with Na₂S is a rapid and effective process under alkaline conditions, while Au remains in solution and Cu and Ag are partially removed, indicating limited selectivity and the need for further optimization. Therefore, this study provides a basis for developing more environmentally friendly processes for amalgamation tailings.