Research progress of non-cyanide gold leaching in gold mines

With the exhaustion of easy-to-treat gold ore resources, gold ores containing arsenic, carbon, high sulfur, and ultrafine particles have become the focus of gold mining. These difficult-to-treat gold ores have poor leaching effects through conventional cyanide leaching methods. The chemicals involved in the production process are highly toxic, which can endanger human health and seriously pollute the ecological environment. Some countries and regions have restricted or prohibited the use of cyanide to extract gold; besides, cyanide treatment contains copper, zinc, nickel, etc. When removing impurities from gold ores, these impurity metals will increase the consumption of cyanide and oxidant in the leaching system. At the same time, a film will be formed on the gold surface that hinders the leaching of gold in cyanide and reduces the leaching rate of gold. Gold-containing substances that are insoluble in the cyanide solution include antimony compounds, aurostibite, black bismuth gold ore, and gold-containing compounds formed during reduction roasting of lead, antimony, and arsenic minerals. Although these compounds are present in small quantities, they may account for a large proportion of the amount of gold lost during processing. Nevertheless, the cyanidation method is currently the main process for processing gold ores. Due to the existence of defects in the cyanidation method and the declining gold ore suitable for cyanide treatment, scholars from all over the world are studying alternatives for gold leaching to realize an efficient and environment-friendly recovery of gold in difficult-to-treat gold mines. This article summarized the methods of non-cyanide leaching of gold: thiosulfate method, glycine method, halide method, lime sulfur mixture method, iodination roasting process, biological oxidation thiourea leaching method, and non-aqueous gold leaching method. The gold leaching principles of seven non-cyanide gold leaching methods and the latest research progress in refractory gold mines were introduced. The development direction of non-cyanide leaching gold technology was prospected based on the problems of non-cyanide gold leaching methods such as expensive leaching agent, difficulty in recovering gold in leaching solution, complicated leaching system, unstable properties of leaching agent, and large consumption.