Pyrometallurgy is a branch of extraction metallurgy . It involves the thermal treatment of minerals and metallurgical ores and concentrates to bring about physical and chemical changes in the material to enable the recovery of valuable metals. [1] Pyrometallurgy treatment can produce products that can be sold as pure metals, or intermediate compounds or alloys , suitable as feed for further processing. Examples of elements extracted by Pyrometallurgy processes include oxides of less reactive elements such as iron , copper , zinc , chromium , tin , and manganese . [2]
Pyrometallurgical procedures are generally classified into one or more of the following categories:
- To calm down,
- roast,
- smelting,
- purification
Most Pyrometallurgy processes require energy input to maintain the temperature at which the process occurs. Energy is usually provided in the form of combustion or by electric heating. When sufficient material is present in the feed to maintain the process temperature by exothermic reaction (i.e. without involving fuel or electrical heating), the process is said to be “autogenous”. Processing of some sulfide ores exploits the exothermicity of their combustion
Cook
Calcination is the thermal decomposition of a material. Examples include the decomposition of hydrates such as ferric hydroxide into ferric oxide and water vapor. Decomposition of calcium carbonate into iron oxide from iron carbonate along with calcium oxide and carbon dioxide:
CaCO 3 → CaO + CO 2
Calcination processes are carried out in various furnaces including shaft furnaces, rotary kilns and fluidized bed reactors .
Roast
Roasting consists of thermal gas–solid reactions, which may include oxidation, reduction, chlorination, sulfation, and pyrohydrolysis.
The most common example of roasting is the oxidation of metal sulfide ores. Metal sulfides are heated in the presence of air to a temperature that causes the oxygen in the air to react with the sulfides to form sulfur dioxide gas and solid metal oxides. The solid product obtained by roasting is often called ” calcine “. In oxidation roasting, if the temperature and gas conditions are such that the sulfide feed is completely oxidized, the process is known as ” dead roasting “. Sometimes, in the case of pre-treated reverberatory or electric smelting furnace feeds, the roasting process is performed with less oxygen than is required to completely oxidize the feed. In this case, the process is referred to as ” partial roasting “.This is because the sulfur is only partially removed. Finally, if the temperature and gas conditions are controlled such that the sulfides in the feed react to form metal sulfate instead of metal oxide, this The process is known as ” sulfation roasting “. Sometimes, the temperature and gas conditions can be maintained such that a mixed sulfide feed (for example a feed containing both copper sulfide and iron sulfide) is thus reacts with one metal to form sulfate and the other to form oxides, a process known as ” selective roasting ” or ” selective sulfation “.
Smelting
Smelting involves thermal reactions in which at least one product is the molten phase.
Metal oxides can be melted by heating with coke or charcoal ( in the form of carbon ), a reducing agent that liberates oxygen as carbon dioxide, leaving a refined mineral . Concerns about carbon dioxide production are only a recent concern , following the identification of an increased greenhouse effect .
Carbonate ores are also smelted with charcoal, but sometimes need to be calcined first. [ citation needed ]
Other materials may need to be added as a flux, to aid in the melting of oxide ores and the formation of slag , as the flux reacts with impurities, such as silicon compounds. [ citation needed ]
Smelting usually occurs at temperatures above the melting point of the metal, but the processes vary greatly according to the ore involved and other matters.
Refining
Refining is the removal of impurities from a material by a thermal process. This includes a wide range of processes involving different types of furnace or other plant.
The term ” refining “
The term ” refining ” can also refer to certain electrolytic processes. Accordingly, some types of Pyrometallurgical refining are called ” fire refining “.
