Gold Ore Beneficiation: Unlocking the Door to Gold Extraction

Gold ore beneficiation is a critical process for extracting gold from gold-bearing ore. The characteristics of different gold ores determine the appropriate beneficiation processes for each. Currently, the primary gold ore beneficiation processes include gravity separation, flotation, and cyanidation, all of which play significant roles in gold extraction.

Gravity separation utilizes the density difference between gold and gangue minerals for separation. Gold has a higher density, typically around 19.3 g/cm³, significantly higher than common gangue minerals such as quartz and feldspar. Gravity separation equipment varies; jigs use periodic up-and-down pulsating water flows to stratify mineral particles by density, with coarse gold particles settling first and being collected; sluices have a simple structure, where slurry flows along an inclined surface, and gold particles settle at the bottom due to gravity; shaking tables utilise asymmetric reciprocating movements of the bed surface and lateral water flow to achieve precise separation of minerals based on density and particle size; centrifugal concentrators rely on strong centrifugal force to enhance gravitational effects, effectively recovering fine-grained gold. Gravity separation is a simple, cost-effective, and environmentally friendly process that does not use chemical reagents, making it environmentally friendly. It is particularly suitable for processing placer gold deposits and coarse-grained rock gold deposits. For example, in some placer gold deposits, gravity separation can directly recover a large amount of coarse-grained gold, serving as an important preliminary enrichment method. However, gravity separation is less effective in recovering fine-grained gold (e.g., particles smaller than 0.01 mm), and single-stage gravity separation often fails to produce high-grade concentrate, necessitating its combination with other processes.

Flotation is based on the differing surface properties of gold minerals and gold-bearing sulphides (such as pyrite and arsenopyrite) to achieve separation. During the flotation process, various reagents play a critical role. Collectors, such as xanthates (e.g., isopentyl xanthate), have thiol groups (-SH) in their molecular structure that selectively adsorb onto the surfaces of gold minerals, enhancing their hydrophobicity and facilitating their attachment to bubbles. Black xanthate not only functions as a collector but also has frothing properties, making it effective in the flotation of arsenic-bearing gold ores. Adjusting agents, such as lime, are used to adjust the pH of the slurry to an alkaline range (typically pH 9–11), suppressing the flotation of silicate gangue while creating an optimal reaction environment for other reagents. Inhibitors such as cyanide can suppress sulfides and are commonly used when prioritising gold flotation. The flotation machine is the core equipment for flotation. Small and medium-sized plants typically use air-suction agitation flotation machines (e.g., SF type), which can self-suction air and have strong agitation force; large plants prefer air-injection agitation flotation machines (e.g., KYF type), which achieve higher flotation efficiency through external air injection. Floating has excellent collection capacity for fine-grained gold, effectively concentrating gold in sulfide concentrates. It is suitable for most rock gold ores and associated gold ores, particularly those classified as ‘poor, fine, and complex’ types of ore. However, flotation has the issue of high reagent consumption. For carbon-containing ores, carbon can adsorb gold minerals, causing ‘gold hijacking’ and reducing gold recovery rates. In such cases, ore pre-treatment is often required, such as roasting or bacterial oxidation, to eliminate carbon interference.

The cyanidation method utilises cyanides (such as sodium cyanide or potassium cyanide) to react chemically with gold in an alkaline environment, forming soluble gold-cyanide complexes, thereby dissolving gold from the ore. Agitation cyanidation is suitable for processing high-grade, finely ground gold ore. In an agitation tank, the cyanide solution is thoroughly mixed with the slurry, allowing gold to dissolve rapidly with a relatively short leaching cycle, typically ranging from a few hours to several dozen hours. Heap leaching cyanidation is targeted at low-grade, large-scale gold ore deposits. The ore is piled into a heap of a certain height, and cyanide solution is sprayed over it. The solution penetrates the ore and dissolves the gold within. This method has a simple process but a longer leaching cycle, typically requiring several weeks to several months. Cyanide leaching has high efficiency and is highly effective for treating oxidised gold ore, fine-grained disseminated gold ore, and flotation concentrates, with conventional leaching rates exceeding 90%. However, cyanide is highly toxic and poses significant risks to the environment and human health. Strict wastewater treatment systems must be in place during use to remove residual cyanide, which inevitably increases production costs and environmental pressure. Additionally, for ore containing high levels of impurities such as arsenic and sulphur, the cyanide leaching method has limited applicability and often requires pre-treatment to enhance gold leaching efficiency.