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Chapter 7. Development of Copper Industries in Mongolia

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Chapter 7. Development of Copper Industries in Mongolia DATA COLLECTION SURVEY ON COPPER INDUSTRY SECTOR IN MONGOLIA FINAL REPORT Chapter 7. Development of Copper Industries in Mongolia 7.1 Copper Smelting There are two types of copper smelting process, one is pyrometallurgical process and the other is hydrometallurgical process. There are two types of ores, one is sulfide ores and the other is oxides ores (see Chapter 2 and Chapter 5). Sulfide ores are processed by the pyrometallurgical process, and oxide ores are processed by the hydrometallurgical process. Production of copper by the pyrometallurgical process accounts for approximately 80% of the total copper production in whole world. Pyrometallurgical process is applied to sulfide ores. The majority of copper ore is chalcopyrite (CuFeS2). As it is understood from the chemical formula of copper sulfide ore, the chalcopyrite type copper ore is sulfide and many iron (Fe) components are included as impurities. Blister copper can also be produced by oxidizing the copper ore by the procedures that sulfur (S) in the copper ore is oxidized and converted into SO2 gas and removed in the form of SO2 gas and that iron (Fe) is converted into iron oxide substances by the oxidation and slag (complex oxides of iron and silica) is produced by adding silica (SiO2) and removed in the form of slag after reduced copper oxide in the slag into metallic copper and separated from slag. However, the copper oxide has a tendency of moving into slag, and as the copper ore contains large quantities of Fe, a lot of slag is generated and copper losses in the slag will be increased accordingly. For the purpose of reducing the copper loss in the pyrometallurgical smelting of copper, it is the procedure employed that the matte (mixtures of Cu sulfide and Fe sulfide) is to be produced at an intermediate step in lieu of oxidizing impurities (Fe, S) completely and directly concentrating Cu, and the majority of Fe is to be removed in the form of slag (complex oxide of Fe and Si) then the matte is to be oxidized and metallic copper is produced. Pyrometallurgical process consists of smelting process and electrolytic refining process. Smelting process consists of matte making from copper ores, converting process to produce blister copper from matte, and the process to produce anodes to be used for electrolytic refining after reducing sulfur and oxygen in blister copper. The advantages of this process, the recovery rate of copper and precious metals is high. More than 99.99% purity electrolytic copper (cathode) is produced by electrolytic refining. Hydrometallurgical process is applied to the oxide ores. Copper leached into sulfuric acid solution and this copper contained in the solution is selectively recovered by SX-EW method which is recovering metallic copper by means of Electro Winning Method. Precious metals cannot be recovered by this process. Pressurization method and chloride method etc. are under development 7-1 CHAPTER 7 DATA COLLECTION SURVEY ON COPPER INDUSTRY SECTOR IN MONGOLIA FINAL REPORT for recovering metallic copper from sulfide ores. Precious metals recovery process is also under development. Precious metals cannot be recovered. Pressurization method and chloride method etc. are under development from sulfide ores. Precious metals recovery process is also under development. The construction cost of hydrometallurgical process is smaller than that of pyrometallurgical process since the blister copper producing process can be omitted in the hydrometallurgical process, and the consumption of fuel, etc. is lower than the pyrometallurgical one as its advantages. In the pyrometallurgical process, it is required to refine blister copper produced to the grade of cathode copper. And, it is necessary to recover metallic copper concentrated into the solvent solution in the hydrometallurgical process. The electrolysis is applied as the chemical processing in both processes. The refining from anode copper to cathode copper is carried out by electrolysis in which anode copper is installed at the positive terminal and pure copper plate or stainless plate is installed at the negative terminal. For the recovery of copper from solvent solution in which copper is concentrated, the electrolysis is to be carried out by installing insoluble electrode at the positive terminal and installing stainless plate at the negative terminal. The method for recovering copper by installing blister copper at the positive terminal is called the electrolytic refining, and that for recovering metals from electrolytic solution by installing insoluble anode at the positive terminal is called the electro-winning. In the electro-winning by means of sulfuric acid solution, oxygen gas is generating at the positive terminal. As the energy to generate oxygen gas is required, a higher voltage of electrolytic cell is required and unit consumption of electric power becomes higher accordingly. 7.1.1 Pyrometallurgical Process (method of matte production) There are various types of pyrometallurgical process and the matte is to be produced in all of such types. Copper ores are melted, and matte and slag are produced to concentrate Cu into matte and Fe into slag and then slag is to be removed and matte is to be recovered after the separation of slag from matte according to the difference of their specific gravities. Most of precious metals are migrated to the matte, and the recovery rate of precious metals is high as the characteristic feature accordingly. Heavy metals which are likely to be oxidized are fixed in the slag as the form of steady complex oxides. The sulfur is oxidized to sulfur dioxide (SO2) transferred to the off gas line. High concentrations of SO2 gas is used as a sulfuric acid production, low concentrations of SO2 gas is recovered as gypsum. Most of the copper loss is due to mixing of matte into the slag. As the constructions of larger smelters have been proceeded in order to save the cost of smelting, small 7-2 CHAPTER 7 DATA COLLECTION SURVEY ON COPPER INDUSTRY SECTOR IN MONGOLIA FINAL REPORT scaled mountainside smelters which belong to mines have lost their cost competitiveness. Moreover, according to the development of floatation and to the increase of distance from the mine to the smelter, it became a basic concept to reduce the transportation cost by reducing the quantity for transportation. The ore flotation process is adopted for cost reduction technique by decreasing the ore traffic volume At the initial stage of the pyrometallurgy, matte is produced by heating and melting lump ores, etc. by using blast furnace, reverberatory furnace, electric furnace, etc. In accordance with the development of floatation method, powdered copper concentrates are mainly being used in the smelter. Powdered copper concentrates have the characteristic that heat spread easily to the inter-granular part because their surface area is large and the mass is small. The ore melting process had been developed by utilizing such characteristics. Several different ore melting methods in which the heat of oxidation reaction of sulfur in sulfide ores is fully utilized by blowing ore and flux into the furnace center with oxygen enriched air ware developed, such as, the flash furnace, the MI furnace, the INCO furnace, the Teniente furnace, the Ausmelt furnace, and the Isasmelt furnace, etc. The pyrometallurgical process can be classified into the process to produce matte, that to produce blister copper by oxidization of matte as well as removal of sulfur and iron, electrolytic refining process to produce cathode copper by reducing sulfur, iron and other impurities in blister copper. The MI furnace is a combination of furnaces finally producing blister copper, and other furnaces are to produce matte. Blister copper is produced from matte. Blister copper is produced by removing iron and sulfur from matte by using PS converter (Peirce-Smith converter) or FC furnace (Flash Converter). The FC furnace had been developed and implemented by applying the technology of flash furnace so as to process matte in the stationary type furnace since PS converter had difficulty in preventing the contamination of environment. The first FC converting furnace had been commissioned in 1995 at Rio Tinto, Kennecott Utah Copper in Magna, UT, USA. Transition of smelting process (production of matte) is shown in figure 7.1.1. (Source: Prepared by Survey Team) Figure 7.1.1 Transition of Smelting Process (matte production process) 7-3 CHAPTER 7 DATA COLLECTION SURVEY ON COPPER INDUSTRY SECTOR IN MONGOLIA FINAL REPORT The structure and the specific feature of pyrometallurgical processes are introduced as follows. (1) Flash Smelting Furnace Flash smelting furnace had been developed and operated for practical use at first in the world as the furnace for processing powdered copper ores. This furnace had been constructed at the Harjavalta smelter of the Outokump Oy Co., Ltd. of Finland in 1949. There are two types of the flash smelting furnaces classified depending on differences of the blowing method. One is Outokump method and another is INCO method. In the Outokumpu method, the furnace has the structure that dry copper concentrates are blown in with the heated oxygen enriched air to the furnace form the top of the reaction shaft. On the other hand, in the INCO method, the furnace has the structure to blow in concentrates from both the right and the left ends of the furnace horizontally, and off-gas is exhausted from the center of the furnace. Figure 7.1.2 and Figure 7.1.3 shows the conceptual diagram of the Outokumpu method and that of INCO method respectively. (Source; Flash smelting furnace method, JOGMEC) Figure 7.1.2 Flash Smelting Furnace of Outokumpu Method 7-4 CHAPTER 7 DATA COLLECTION SURVEY ON COPPER INDUSTRY SECTOR IN MONGOLIA FINAL REPORT (Source; Flash smelting furnace method, JOGMEC) Figure 7.1.3 Flash Smelting Furnace of INCO Method Among these two flush smelting furnaces, Outokumpu type smelting furnaces are major ones presently being used most popularly.
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