Gold is a valuable strategic resource with commodity and financial value, and plays an important role in the development of national economy and social progress. As gold resources continue to dry up, refractory gold ore has gradually become the main mining object. People generally call gold ore with a conventional gold cyanide leaching rate of no more than 80% as hard-to-treat gold ore. Copper-gold ore is a typical refractory ore, and it is also an important gold resource in China. China's gold-producing bases in Shandong, Henan and other provinces store a large amount of copper-bearing gold ore, and copper ore in copper bases in Jiangxi, Anhui and Hunan in the middle and lower reaches of the Yangtze River is generally associated with gold. Copper-bearing gold ore has high copper content and copper consumes a large amount of cyanide in the cyanidation leaching process, resulting in a low gold leaching rate or rising leaching costs, making gold extraction economically unfeasible; another formation with CN- Copper cyanide ion affects subsequent operations. Therefore, before the cyanide leaching of copper-bearing gold ores, it is necessary to take necessary measures to remove the effect of copper [1-6]. Based on the collection of a large number of literatures, this paper analyzes and discusses the theory and practice of the pretreatment process of refractory copper-bearing gold ore, the theory and practice of the leaching process, and the status and progress of industrial treatment of this type of gold ore. 2 Status and progress of pretreatment technologies for refractory copper-bearing gold ores
The extraction process of refractory copper-bearing gold ores can be generally divided into the following categories [1.5-10]: ① Direct leaching of ores or flotation concentrates. Because this method contains copper, iron, antimony and other minerals that will dissolve in the cyanide solution and consume a large amount of cyanide and oxygen, the effect is generally not good. Various strengthening measures can be used to improve the direct cyanidation effect, such as using a multi-stage leaching process, using a non-cyanide leaching process, such as thiourea and thiosulfuric acid leaching. ② The ore is enriched with gold and copper by flotation to produce concentrates and sent to the smelter, and gold is recovered in the process of smelting copper. China's associated gold and copper ore are mainly treated by this method. This method has the disadvantages of increasing transportation costs and inevitable loss of concentrates. The recovery rate of gold is generally low and cannot produce finished gold. ③ Gold ore or sorted concentrate is pretreated to remove copper, lead, antimony and other base metals, and then leached with cyanide or other leaching agents. Although this method will make the process more complicated, after the pretreatment and removal of copper, lead, antimony and other metals, the leaching rate of gold can be greatly improved, and other valuable metals can also be recovered. The main pretreatment methods are roasting oxidation method, bacterial oxidation method, pressure oxidation method, chemical oxidation method and so on.
2.1 roasting oxidation method
Roasting oxidation method [11-13] is to oxidize gold-clad sulfide minerals into oxides or sulfates by roasting. Roasting is carried out in a roaster. Generally, the ore is crushed and ground before roasting. After the ore is roasted, the base metal such as copper is leached with water or acid, and then the gold is immersed. The exhaust gas is treated to remove entrained solids, sulfur dioxide, and possible volatiles. If economically advantageous, these components can be processed into goods. The roasting of copper-containing gold ore is generally performed at low temperature to generate copper sulfate and reduce the formation of S02. The use of sulfated roasted copper concentrate or oxidative roasting to treat gold extraction from flotation gold concentrate has been practiced in industry for many years. China's Zhaoyuan Gold Smelter and Zhongyuan Gold Smelter both use the sulfuric acid roasting-cyanide leaching process. The roasting temperature is in the range of 670 ° C-720 ° C. The copper in the roasting sand is leached with an acidic aqueous solution, and the sulfur dioxide produced is used to produce sulfuric acid.
The roasting oxidation method is the most traditional pretreatment method. With the advancement of technology and market demand, this method has obtained new development in recent years, from single-hearth furnace to multi-hearth furnace, from fixed-bed roasting to fluid boiling roasting to flash roasting. From air roasting to oxygen-enriched roasting [15-17].
In order to improve the leaching rate of copper, some domestic units have studied the roasting with chlorinated salt or sulfate, and obtained good test results. Literature  reported on the leaching of copper-containing gold concentrates from a gold mine in Guangdong with sodium sulfate roasting pretreatment. The copper leaching rate was above 95% and the gold leaching rate was 97%. This shows that sulphate roasting can simultaneously increase the leaching rate of gold and copper. Literature  reported on the roasting pretreatment leaching of a flotation gold concentrate with sodium chloride in a certain mine in Shandong, and the results showed that the leaching rates of copper, gold, and silver were respectively 8.5%, 2.31%, and 44.07% higher than those of ordinary roasting. At the same time, the process can greatly reduce the acid consumption, easily realize the comprehensive recovery of gold, copper and sulfur concentrates, and has less process pollution, simple processes and easy industrialization.
The roasting oxidation method has the advantages of fast processing speed, strong adaptability (suitable for refractory gold ores containing sulfur, arsenic and carbon), reliable technology, simple operation, and recyclable by-products. The disadvantage is that it is more sensitive to changes in operating parameters and feed ingredients, and it is easy to cause over-burning or under-burning. Partial sintering of the roasted sand occurs during over-burning, which causes the porosity of the roasted sand to be closed, which causes the gold minerals to be enveloped twice, resulting in a decrease in the leaching rate of gold; a large amount of harmful gases such as S02 will be released during the roasting process, which will remove harmful substances from the roasting process The cost of gas is high. If the comprehensive recovery is not good, it will seriously pollute the environment. Roast oxidation methods are being challenged by more environmentally friendly pretreatment processes.
2.2 Microbial oxidation method
Microbial oxidative pretreatment removes copper, zinc and other metals from polymetallic sulfide ore raw materials. Aerobic Thiobacillus acidophilus bacteria play a very important role. They strengthen electrochemical interactions and oxidize sulfide minerals to sulfur first and then to sulfate. Sulfuric acid, sulfide, and divalent iron produced during the bacterial oxidation process can be used as the energy source for bacteria. This process oxidizes metal sulfides such as copper that is wrapped with gold to dissolve sulfates, basic sulfates, etc., thereby exposing the gold minerals. [1.20-24], metal ions such as copper can be leached, and the leaching slag is then recovered by wet metallurgy.
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