preface


In today's world, gold, as a special financial strategic reserve, has a very important impact on the national economy. In addition, gold is widely used in decoration, aerospace, electronic communication and other fields because of its excellent physical and chemical properties. With the rapid development of economy, the demand for gold is increasing, and the traditional easy to treat gold resources are drying up, which will gradually fail to meet the increasing demand of society for gold. Therefore, extracting gold from relatively difficult gold resources has become a widely studied topic all over the world. There has been a brief introduction to the traditional method of extracting gold from refractory gold ores before - the gold leaching process of refractory gold ores. Here we will introduce in detail the principle and process of the relatively advanced "matte making and gold catching" method to treat refractory gold ores.



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Principle of matte making and gold capture


The term "matte making and gold capture" comes from the oxygen bottom blowing copper smelting or lead smelting technology. The product copper matte or lead matte can capture precious metals, including Au, Ag, platinum group metals, etc. There are few reports on the thermodynamics of matte blowing, and there is little research on the principle of matte blowing.



In platinum group metal metallurgy, Liu Shijie believes that the principle of base metals capturing precious metals is that "platinum group metals and gold, silver and iron and heavy non-ferrous metals copper, nickel, cobalt and lead have similar lattice structure and similar lattice radius, and can form continuous solid solution alloys or intermetallic compounds in a wide range of components. Therefore, base metals in molten state and their binary or multicomponent alloys are effective and reliable collectors of precious metals".



Li Dingxin and others pointed out in precious metals extraction and refining that the atomic radius also plays a role, pointing out that "copper is a body centered cubic structure, and the atomic radius is also close to that of platinum group metals. It can form solid solutions with platinum, palladium and rhodium, and can dissolve a certain amount of iridium".



In structural chemistry, Zhou Gongdu et al. Put forward the view that the capture of precious metals by base metals is a high-temperature extraction process. Taking carbon disulfide as an example, they believe that lead can capture precious metals because precious metals are easy to dissolve in lead, just as iodine is easy to dissolve in carbon disulfide.



Chen Jing, academician of the Chinese Academy of engineering, pointed out that these views are based on the same or similar physical characteristic parameters such as crystal form, cell parameters and atomic radius of precious metals and base metals, which can be used as the "principle" for base metals to capture precious metals, but he believes that these parameters can not be used as the necessary and sufficient conditions for the capture principle. He discussed the principle of noble metal capture by base metal phase and matte phase in Pyrometallurgical smelting process from the micro level, and pointed out that the capture effect is due to the great difference in the composition and structure of molten slag phase and base metal phase. The slag phase is composed of gangue mineral components SiO2, MgO, Cao and FeO produced in smelting. They form molten silicate, a molten glass. The slag phase binds silicon, oxygen atoms and Ca2 +, Mg2 +, Fe2 + plasma by covalent and ionic bonds, and the bond electrons are localized electrons. Because the valence electrons of noble metals or the hanging bonds on the surface of atomic clusters cannot bond with the surrounding localized electrons, noble metal atoms cannot exist stably in the slag. The metal phase binds atoms together by metal bonds, and the electrons between atoms can flow freely. The bond electrons of precious metals can bond with the bond electrons of surrounding base metal atoms, disperse into the molten base metal phase with disorderly stacking structure, and reduce the free energy of the system. Matte has quite high conductivity at high temperature (the value is in the range of 103 ~ 104s / cm), and the temperature coefficient is negative, which belongs to electronic conductivity. Because the nature of matte is similar to that of metal, during matte making and smelting, precious metal atoms enter matte instead of slag. Moreover, due to the electronegativity of noble metals and high standard electrode potential, noble metal compounds will be reduced before base metal compounds in reduction smelting; The base metal will be oxidized in oxidizing smelting. Therefore, in the smelting process of sulfide ore, precious metal atoms first enter the matte phase, then enter the coarse metal, and finally enter the anode mud.



Process flow of matte making and gold capture anode slime treatment



Taking copper matte as an example, gold in refractory gold ore was extracted by mixing gold bearing refractory concentrate with copper concentrate and oxygen bottom blowing copper smelting anode slime treatment.



Bottom blowing matte gold capture process


Under the high temperature of 1150 ℃ ~ 1250 ℃, the ingredients such as gold bearing copper concentrate (copper concentrate and refractory concentrate), quartzite and slag concentrate react with the blown oxygen enriched air in the bottom blowing smelting furnace. The cuprous sulfide (Cu2S) in the furnace charge and the non oxidized ferrous sulfide (FES) are mainly Cu2S FES and dissolved with gold Copper matte, a co melt of precious metals such as silver and a small amount of other metal sulfides (such as ZnS and PBS) and trace iron oxides (FeO and Fe3O4), while gangue components (SiO2, Cao, MgO and Al2O3) in the charge form liquid slag together with FeO (oxygenate melt dominated by iron olivine 2FeO · SiO2). Copper matte does not melt with slag, and the density of slag is smaller than that of copper matte, so as to achieve separation.



After a series of treatment of copper matte, copper becomes the finished product - cathode copper, and precious metals such as gold and silver are enriched into anode mud for recovery.



Process flow of gold bearing copper concentrate


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The main components of gold bearing copper concentrate of an enterprise are shown in Table 1


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The composition of copper matte in an enterprise is shown in Table 2:


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The main components of crude copper in an enterprise are shown in Table 3:


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It can be seen that the gold in the refractory gold ore in the raw material is enriched by the "matte making and gold catching" technology, enters the copper matte, then enters the crude copper, and finally enters the anode mud in the electrolytic process.



Anode slime treatment


Anode slime treatment adopts pressure leaching, alloy converting, silver electrolysis and gold refining to produce gold ingots and silver ingots. Firstly, the anode slime is pre leached and pressure leached in the pressure leaching section. After the leaching pulp is filtered, the filtrate is returned to the electrolysis workshop. After filtration and drying, the filter residue is sent to the oxygen oblique blowing rotary converter in the alloy converting process. The gold and silver alloy plates produced are sent to the silver electrolytic cell for treatment. Silver ingots and anode slime are produced by silver electrolysis, and gold ingots are produced by chlorination.



Process flow of gold and silver production by anode slime treatment:


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The main components of anode slime of an enterprise are shown in Table 4:


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summary


With the continuous development and utilization of mineral resources, the traditional easy to treat gold resources are gradually exhausted. "Matte making and gold catching" can provide new ideas and methods for the extraction of gold from difficult to treat gold mines. Compared with traditional methods, the gold extraction process of refractory gold ore takes the copper smelting process as the main line, enriches and recovers precious metals at the same time, which has the characteristics of environmental protection and high efficiency. It is an important solution for the gold extraction technology of refractory gold ore in the future.