Three Cyanidation Processes for Gold Extraction

As a classic gold extraction process, cyanidation has undergone over a century of development and refinement since its application in mining production in the late 19th century. With its mature technology, relatively simple workflow, and stable, reliable operation, this method remains one of the mainstream techniques widely adopted in gold ore beneficiation and metallurgy both domestically and internationally. In China, cyanidation similarly holds significant importance, particularly for processing diverse types and grades of gold ores, providing critical technological support for achieving efficient gold resource recovery.

Depending on ore properties and process conditions, cyanidation has evolved into multiple specific applications in industrial practice. Among these, cyanide-carbon-in-pulp (CIP), heap leaching, and stirred cyanidation represent the three predominant process routes currently in use.

Cyanide-carbon-in-pulp (CIP) is a highly efficient gold extraction process combining leaching with adsorption. This method first crushes and grinds the gold ore into a slurry of suitable concentration. Cyanide solution is then added under agitation, dissolving gold in an alkaline environment to form soluble gold-cyanide complexes. Activated carbon is subsequently introduced into the slurry system, utilizing its strong adsorption capacity to concentrate and recover gold. After desorption treatment of the gold-loaded carbon, a high-grade gold-bearing solution is obtained, from which gold is ultimately extracted via methods such as electrolytic deposition. This method is particularly suitable for processing ores with high clay content and difficult solid-liquid separation, offering advantages such as high recovery rates and a compact process flow.

The cyanide heap leaching method primarily targets low-grade gold ores or resources like mineral processing tailings. It is a large-scale gold extraction technology requiring relatively low investment and operating at a lower cost. During processing, ore is typically crushed to an appropriate particle size and piled on a pre-laid impermeable liner. Cyanide leachate is uniformly distributed over the ore pile surface via spraying or drip irrigation. As it permeates downward, it contacts gold minerals and initiates dissolution reactions. The gold-bearing leachate collected at the heap base is conveyed to subsequent processing stages, where gold is recovered through methods such as activated carbon adsorption and zinc replacement. This process demands low ore grade and can process mineral resources that are difficult to recover economically using traditional methods, making it significant for comprehensive resource utilization.

Agitated cyanidation, often termed pre-leaching, is typically conducted in a series of continuous leaching tanks. Its core principle involves mechanically agitating the cyanide solution to enhance contact with finely ground ore, accelerating gold dissolution. The effectiveness of this method is influenced by multiple factors: slurry concentration must be controlled within an optimal range to ensure good flowability and reaction interface; slurry pH is typically maintained in an alkaline environment (approximately 10-11) to promote cyanidation while suppressing harmful gas generation; dissolved oxygen concentration is a key factor affecting gold dissolution rates, often regulated through aeration or the addition of oxidants; Appropriate pulp temperature enhances reaction kinetics, though economic viability and operational safety must be balanced; sufficient leaching time ensures near-complete gold dissolution; and the occurrence state, particle size, and surface cleanliness of gold minerals directly determine the accessibility and efficiency of the cyanidation reaction, making fine grinding and oxidation pretreatment of ore often critical.

In summary, despite its long history, cyanide gold extraction technology continues to play an irreplaceable role in gold recovery through process innovation and optimized operating conditions. With heightened environmental requirements and technological advancements, the future development of this technology will focus on achieving greener and smarter cyanidation processes while maintaining high recovery rates.