Key Takeaways & Executive Findings
- •• A novel gold leaching reagent synthesized from sodium cyanate, sodium hydroxide, and sodium ferrocyanide achieves high leaching rates (87.56% for roasted gold concentrate, >90% for electronic waste) as a safer alternative to cyanide. • The reagent exhibits excellent selectivity for gold over other metals, reducing co-dissolution and simplifying downstream recovery. • Synthesis conditions (mass ratio 15:3:1, 600°C, 1 h) are optimized, and the effective component is identified as sodium isocyanate. • This development addresses the toxicity and safety concerns of cyanide, offering a promising eco-friendly solution for gold extraction from ores and electronic waste.
Abstract
Cyanide is the most widely used reagent in gold production processes. However, cyanide is highly toxic and poses safety hazards during transportation and use. Therefore, it is necessary to develop gold leaching reagents that can replace cyanide. This paper introduces a method for synthesizing a gold leaching reagent. Sodium cyanate is used as the main raw material, with sodium hydroxide and sodium ferrocyanide used as additives. The gold leaching reagent can be obtained under the conditions of a mass ratio of sodium cyanate, sodium hydroxide, and sodium ferrocyanide of 15:3:1, synthesis temperature of 600°C, and synthesis time of 1 h. This reagent has a good recovery effect on gold concentrate and gold-containing electronic waste. The gold leaching rate of roasted desulfurized gold concentrate can reach 87.56%. For the extraction experiments of three types of gold-containing electronic waste, the gold leaching rate can reach over 90% after 2 h. Furthermore, the reagent exhibits good selectivity towards gold. Component analysis indicates that the effective component in the reagent could be sodium isocyanate.
1. Introduction
Gold, a rare and precious metal, is not only utilized for reserves and investments [1], but also plays a pivotal role in modern industries like telecommunications and aerospace [2]. The extraction of gold primarily relies on hydrometallurgical methods, wherein cyanide leaching significantly dominates the process [3–5]. Cyanide leaching involves employing a cyanide solution as a solvent to extract gold from the ore, followed by the recovery of gold from the resulting pregnant solution. Since the breakthrough discovery in 1887 that cyanide solutions can dissolve gold, cyanidation has a nearly century-long history in gold extraction. This method is well-developed, having the advantage of high gold leaching rates, strong adaptability to ores, and low costs, making it the predominant method in gold production to this day [6].
The process of gold extraction using cyanide primarily involves two steps: cyanide leaching and gold deposition [7]. Cyanide leaching occurs when gold in the ore reacts with cyanide in the presence of an oxidant (typically oxygen), forming gold-cyanide complexes that dissolve into the solution. This process is represented by the chemical reaction (1): 4Au(s)+8CN−(aq)+O2(g)+2H2O(l) → 4[Au(CN)2]−(aq)+4OH−(aq) (1). Commonly used cyanide reagents include sodium cyanide, potassium cyanide, ammonium cyanide, calcium cyanide, and cyanide melts. Gold deposition refers to the extraction of gold from the cyanide solution and can be achieved through various methods such as activated carbon adsorption [8–9] (carbon-in-pulp, CIP, and carbon-in-leach, CIL), zinc displacement (zinc wires or zinc powder), electrolytic deposition, ion-exchange resin [10–11] (resin-in-pulp, RIP, and resin-in-leach, RIL), and magnetic carbon method. Among these methods, zinc displacement and activated carbon adsorption are traditional gold deposition techniques widely employed in gold mines [7].
The structure of the cyanide ion is linear, and its highest occupied molecular orbital (HOMO) is a σ bonding orbital formed by the hybridization of the s–p orbitals of carbon and nitrogen atoms. The lowest unoccupied molecular orbital (LUMO) is a π antibonding orbital formed by the p orbitals of carbon and nitrogen atoms [12], as shown in Fig. S1. Therefore, the cyanide ion not only donates a lone pair of electrons during leaching but also has the ability to accept metal π electrons, forming stable coordination compounds with various metal ions [13–14]. Cyanide can form coordination compounds not only with gold ions but also with silver, copper, zinc, nickel, and other metals [15]. Consequently, cyanide ions can quickly bind with trivalent iron in the cytochrome oxidase of living organisms, preventing its reduction to divalent iron and interrupting the electron transfer process, leading to cell asphyxiation and respiratory failure, which is the fundamental reason for the high toxicity of cyanide to living organisms [16]. Cyanide is categorized as a highly toxic hazardous chemical. According to literature reports, the lethal dose of sodium cyanide is 1–10 mg/kg [17–19], posing safety risks during use and transportation [20]. Therefore, it is necessary to develop low-toxicity leaching reagents as alternatives.
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Jinlin Li, Chunbao Sun, Jue Kou, Peilong Wang, Xinyu Liu (2025). Development of a gold leaching reagent as an alternative to cyanide: Synthesis and performance evaluation. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-024-2957-x
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Frequently Asked Questions
What is the main purpose of the gold leaching reagent developed in this study?
The reagent is designed as a safer alternative to cyanide for gold leaching, aiming to reduce toxicity and safety hazards while maintaining high leaching efficiency.
What are the key synthesis conditions for the gold leaching reagent?
The reagent is synthesized using sodium cyanate, sodium hydroxide, and sodium ferrocyanide in a mass ratio of 15:3:1, at a temperature of 600°C for 1 hour.
How effective is the reagent in leaching gold from different materials?
It achieves a gold leaching rate of 87.56% for roasted desulfurized gold concentrate and over 90% for three types of gold-containing electronic waste after 2 hours.
What is the effective component responsible for gold leaching?
Component analysis indicates that the effective component in the reagent is likely sodium isocyanate.
Does the reagent show selectivity towards gold?
Yes, the reagent exhibits good selectivity towards gold, which is beneficial for reducing co-dissolution of other metals and simplifying downstream processing.
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