Characterization of Gold in Complex Historical Refractory Tailings for Enhanced Process Optimization

Abstract

Historical gold tailings show promise as a secondary resource amid declining primary deposits, yet conventional cyanidation falls short, resulting in recoveries below 90%. An essential pre-treatment process is crucial for optimal recovery, contingent on understanding the complex mineralogy of the tailings. This study employs a multidisciplinary approach to thoroughly analyze gold’s refractory behavior in complex historical tailings. Using operational mineral fractions, cyanide bottle roll tests, aqua regia digestion, diagnostic leaching, and chemical and mineralogical analyses, the research draws material from Witwatersrand’s extensive tailings reservoirs. These reservoirs, exemplifying complexity, exhibit a recovery rate of less than 50% through cyanidation. Findings reveal limited cyanide-amenable gold, with recoveries ranging from 14–61% at ∼0.05 g/t, primarily as micron to nano-sized native gold particles hosted in the slimes mineral fraction (<40 µm). Higher susceptibility to cyanide leaching is observed in recoveries ranging from 14–74% compared to 10–54% in light mineral fractions (<2.95 g/cm3). Non-cyanide amenable forms, such as sulfides and silicates, contribute to refractory behavior at 4–38% (∼0.09 g/t) and 11–32% (∼0.05 g/ton) respectively, with varying gold distributions across different tailings dumps. This suggests that a pre-treatment step, combined with tailored leaching in the metallurgical flowsheet, would substantially improve gold recoveries beyond 60%. The investigations in this study provide a valuable analytical tool for determining the amenability of complex historical gold tailings to different pretreatments, optimizing gold recovery, contributing to sustainable resource management, and maximizing the utilization of this valuable gold resource.