Key Takeaways & Executive Findings
- •• Microwave roasting self-leaching achieves 96.18% gold extraction from high-sulfur refractory gold ore without cyanide. • Response surface methodology identifies CuSO4 and NH3·H2O as critical factors influencing the self-leaching process. • XPS analysis reveals that sulfide, polysulfides, and thiosulfate act as key ligands in gold complexation. • The copper–ammonia complex catalyzes self-leaching, but improper ratios cause copper–sulfur precipitates that lower recovery.
Abstract
Microwave roasting self-leaching is an innovative method for recovering gold from high-sulfur refractory gold concentrates, without using deadly toxic cyanide reagents. However, the mechanism of gold self-leaching, which relies on lixiviants prepared using volatilized sulfur obtained from roasting, has not been fully elucidated. This study employs the response surface methodology to optimize processing parameters, resulting in an increased gold extraction rate of 96.18%. Analytical factorization and the Tafel curve indicate that CuSO4 and NH3·H2O significantly influence the self-leaching process. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis reveals that S2−, polysulfides, and thiosulfate are involved in the gold leaching reaction, with S2− and other sulfur species serving as primary ligands for gold complexation. The role of polysulfides in the early stages of the gold-leaching reaction is also noteworthy. The copper–ammonia complex catalyzes the self-leaching gold reaction; however, an improper addition ratio can lead to copper–sulfur compound precipitates, reducing the extraction rate.
1. Introduction
Gold is primarily obtained through the hydrometallurgical processing of gold ore. High-sulfur refractory gold ore contains gold particles encapsulated within sulfide minerals and is characterized by an extremely fine particle size, on the order of a few microns [1]. Conventional ultrafine grinding processes, which are used to extract these particles, result in high-energy consumption and generate significant amounts of sludge. This, in turn, hinders the leaching and recovery of leachate.
Roasting is the most frequently used pretreatment method for high-sulfur refractory gold ores [2]. During roasting, metal sulfides such as pyrite and chalcopyrite decompose at high temperatures. This breaks down the encapsulating structure and allows the gold particles to contact the leaching agent. Although this method mitigates the sludge problem associated with ultrafine grinding, it produces toxic sulfur oxide gases, posing environmental hazards and high energy costs [3].
Microwave heating, which is recognized as an efficient roasting method, has garnered significant attention in academic research and has become a prominent topic in mineral processing, including limonite reduction [4], vanadium shale pretreatment [5], molybdenum leaching [6], and granite cracking and melting [7]. A previous study [8] has shown that microwave roasting is an energy-efficient and effective pretreatment method for high-sulfur gold concentrates. Amaya et al. [9] demonstrated that microwave roasting of refractory gold ore at the same temperature required only 17%–23% of the time required for traditional roasting, and thereby, power consumption reduced to approximately 22% of that of conventional methods. Similarly, Amankwah and Ofori-Sarpong [10] reported that microwave roasting followed by cyanide leaching significantly improved the gold extraction rate by over 95%. Microwave roasting can effectively remove carbonaceous matter, sulfur, arsenic, and other harmful elements. Compared with traditional roasting, the microwave method substantially reduces the required processing time and enhances efficiency [11–12].
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Zhengyu Liu, Jue Kou, Xiaosong Guo, Wei Liu, Chunbao Sun, Anlin Shao, Chang Liu (2025). Low-toxicity non-cyanide recovering high-sulfur refractory gold ore via microwave roasting self-leaching process: Response surface optimization and mechanism study. Journal of Mineral Metallurgy and Materials Science. https://doi.org/10.1007/s12613-025-3105-y
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Frequently Asked Questions
What is the gold extraction rate achieved in this study?
The optimized process achieved a gold extraction rate of 96.18% from high-sulfur refractory gold ore using microwave roasting self-leaching.
How does microwave roasting self-leaching differ from traditional cyanide leaching?
This method eliminates cyanide by using volatilized sulfur from the roasting step to generate lixiviants (e.g., thiosulfate and polysulfides), providing a low-toxicity and environmentally friendly alternative.
What are the key factors influencing the self-leaching process?
Response surface methodology identified CuSO4 and NH3·H2O as significant factors; the copper–ammonia complex catalyzes the gold leaching reaction.
What is the role of sulfur species in gold leaching?
XPS analysis revealed that sulfide (S2−), polysulfides, and thiosulfate are involved in gold complexation, with these species acting as primary ligands.
Why can an improper addition ratio reduce gold extraction?
An improper ratio can lead to the precipitation of copper–sulfur compounds, which reduces the availability of lixiviants and lowers the gold extraction rate.
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