A review on current practices and emerging technologies for sustainable management, sequestration and stabilization of mercury from gold processing streams

This paper presents an overview of unit processes that lead to potential mercury contamination during gold processing, which can pose serious health, environmental and technical concerns. Mercury release in gold processing streams is attributed to its dissolution from mercury bearing gold ores during cyanide leaching, and its mobile nature in the subsequent stages (e.g., carbon adsorption, elution, Zn precipitation/electrowinning, and smelting) and tailing storage facilities. Although retorting prior to smelting and sulphur-impregnated carbon filters have been developed to ensure minimal mercury contamination, these methods deal with gaseous mercury which is highly toxic and still a serious threat for both the environment and workers. Moreover, spent carbon filters containing high mercury concentrations introduce a new environmental issue. Therefore, there is a demonstrated need for safer and more efficient removal and sequestration techniques. Thus, this work includes a review of mercury removal from activated carbon as well as current mercury treatment and stabilization practices including precipitation, adsorption, cementation, ion exchange and solvent extraction. In addition, emerging mercury remediation materials such as nanomaterials and bimetals with a promising potential in sustainable management, sequestration, and stabilization of mercury from aqueous media will be highlighted. In summary, the results show a high mercury removal capacity of the outlined materials and techniques (between 70 to around 100% removal). However, one of the issues that emerges from these studies is the lack of selectivity of reagents for mercury capture from aqueous solutions containing precious metals. In this regard, future studies with more focus on the selective mercury removal from activated carbon, and then its precipitation from solutions using substances with a greater adsorption capacity to mass ratio (suitable for safe disposal), are therefore recommended.