The occurrence of most gold in an encapsulated state often results in poor extraction efficiency, and efficient pretreatment is the key to effective gold recovery from Carlin-type gold ores. This study investigated the enhancement of citric acid (CA) assisted microwave (MW) roasting on gold extraction from Carlin-type gold ores by sulfide/thiosulfate leaching, primarily analyzing in-situ phase transformation, microstructure characterization, and the thermal decomposition behavior of solids. The results show that gold extraction increases significantly with increasing CA dosage, furnace temperature, and roasting time when heated by MW, reaching a maximum of 87.7% at a CA dosage of 2% and a temperature of 500°C for 60 min in the presence of air. Moreover, extraction is significantly higher with CA than without CA at roasting temperatures below 300°C. The phase transition of gold-bearing pyrite is controlled mainly by temperature when heated by MW without CA, resulting in surface oxidation at 300°C, with significant oxidation at 400°C, and complete transformation into Fe2O3 and SO2 at temperatures over 500°C. Interestingly, CA and its decomposition products of CO2 and H2O induce the generation of unstable intermediates at 100°C, such as FeCO3, FeC21H21O7, and FeOOH. The decomposition of these intermediates at higher temperatures results in the rapid formation of a hematite layer with developed pores at 300°C, which provides more diffusion channels for SO2 and O2, producing coral-like porous hematite particles. Both number of pores and the pore size are larger at 500°C. The combined effect of MW and CA enhances exposed gold content over 70% which in turn increases gold extraction. This work provides significant insights into the enhancement process of gold extraction of CA-assisted MW roasting.

中文翻译：

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通过柠檬酸辅助微波焙烧 Carlin 型金矿石和硫化物/硫代硫酸盐浸出增强黄金提取


大多数黄金以封装状态出现，往往会导致提取效率低下，高效的预处理是从 Carlin 型金矿石中有效回收黄金的关键。本研究研究了柠檬酸 （CA） 辅助微波 （MW） 焙烧对硫化物/硫代硫酸盐浸出从 Carlin 型金矿石中提取黄金的增强，主要分析了原位相变、微观结构表征和固体的热分解行为。结果表明，当微波加热时，随着CA用量、炉温和焙烧时间的增加，金的提取率显著增加，在空气存在下，当CA用量为2%时，温度为500°C，时间最长为87.7%。此外，在低于 300°C 的烘焙温度下，使用 CA 的提取率明显高于不使用 CA 的提取率。 含金黄铁矿的相变主要受温度控制，当MW加热时无CA时，导致表面氧化，在300°C时发生表面氧化，在400°C时发生显著氧化，并在超过500°C的温度下完全转化为Fe2O3和SO2。 有趣的是，CA 及其 CO2 和 H2O 的分解产物在 100°C 下诱导产生不稳定的中间体，例如 FeCO3、FeC21H21O7 和 FeOOH。这些中间体在较高温度下分解导致在 300°C 时迅速形成具有发达孔隙的赤铁矿层，这为 SO2 和 O2 提供了更多的扩散通道，产生珊瑚状多孔赤铁矿颗粒。在 500°C 时，孔数和孔径都较大。 MW 和 CA 的综合作用使裸露的金含量提高了 70% 以上，从而增加了金的提取。 这项工作为 CA 辅助 MW 焙烧的黄金提取增强过程提供了重要的见解。