Metallurgy is a process and technology to extract metals or metal compounds from ores and make metals into metal materials with certain properties through various processing methods. Metallurgical technology mainly includes pyrometallurgy, hydrometallurgy and electrometallurgy. Pyrometallurgy is a high-temperature metallurgical process. Some or all minerals in ore or concentrate undergo a series of physical and chemical changes at high temperature, generating another form of compounds or simple substances, which are enriched in gas, liquid or solid products respectively, thus achieving the purpose of separating the metal to be trapped from impurities such as gangue. Hydrometallurgy is a metallurgical process carried out in solution. The temperature of hydrometallurgy is not high, generally lower than 200 degrees. In the high temperature and high pressure process of modern hydrometallurgy, the temperature is only about 100 degrees, and in rare cases, the temperature can reach 400 degrees. Hydrometallurgy includes leaching, purification, metal preparation and other processes. Electrometallurgy is a method of extracting metals by using electric energy. Electrometallurgy can be divided into electrothermal metallurgy and electrochemical metallurgy according to the different effects of using electric energy. 1. Electrothermal metallurgy is a smelting method that converts electric energy into heat energy. In the process of electrothermal metallurgy, according to the nature of its physical and chemical changes, it is not much different from pyrometallurgy, and the main difference between them is only the different sources of heat energy during smelting. 2, electrochemical metallurgy (electrolysis and electrodeposition) is the use of electrochemical reaction, make the metal from the solution or melt containing metal salts. The former is called solution electrolysis, such as electrolytic refining of actinium and electrowinning of zinc, which can be classified as hydrometallurgy. The latter is called molten salt electrolysis, which not only uses the chemical effect of electric energy, but also converts electric energy into heat energy, thus heating metal salts and melting them, so it can also be classified as pyrometallurgy. The production process of extracting metal from ore or concentrate is usually pyrometallurgical process and wet process. Even pyrometallurgical processes, such as pyrometallurgical smelting of sulfide crucible concentrate, need wet electrolytic refining process. In zinc hydrometallurgy, zinc sulfide concentrate also needs high temperature oxidation roasting pretreatment.
Aluminum is mainly obtained by electrolysis of aluminum trioxide. Because aluminum is active, its oxide free energy of formation is relatively low, which means that the oxide is relatively stable and difficult to be reduced. Therefore, it is difficult to reduce metallic aluminum from alumina by using existing reducing agents (carbon, H2, etc.). ) under heating conditions.