Converting (metallurgy)
Encyclopedia
Converting is a term used to describe a number of metallurgical smelting
processes. The most commercially important use of the term is in the treatment of molten metal sulfides to produce crude metal and slag, as in the case of copper and nickel converting. Another, now uncommon, use of the term referred to batch treatment of pig iron to produce steel by the Bessemer process. The vessel used was called the Bessemer converter.
is treated in converters to oxidize iron in the first stage, and oxidize copper in the second stage. In the first stage oxygen enriched air is blown through the tuyere
s to partially convert metal sulfides to oxides:
Since iron has greater affinity to oxygen, the produced copper oxide reacts with the remaining iron sulfide:
The bulk of the copper oxide is turned back into the form of sulfide. In order to separate the obtained iron oxide, flux
(mainly silica) is added into the converter. Silica reacts with iron oxide to produce a light slag
phase, which is poured off through the hood when the converter is tilted around the rotation axis:
After the first portion of slag is poured off the converter, a new portion of matte is added, and the converting operation is repeated many times until the converter is filled with the purified copper sulfide. The converter slag is usually recycled to the smelting stage due to the high content of copper in this by-product. Converter gas contains more than 10% of sulfur dioxide, which is usually captured for the production of sulfuric acid
.
The second stage of converting is aimed at oxidizing the copper sulfide phase (purified in the first stage), and produces blister copper. The following reaction takes place in the converter:
Copper content in the obtained blister copper is typically more than 95%. Blister copper is the final product of converting.
Horizontal converters of the Pierce-Smith type prevail in the metallurgy
of non ferrous metals. Such a converter is a horizontal barrel lined with refractory material inside. A hood for the purpose of the loading/unloading operations is located on the upper side of the converter. Two belts of tuyeres come along the axis on either sides of the converter.
Molten sulfide
material, referred to as matte
, is poured through the hood into the converter during the operation of loading. Air is distributed to tuyeres from the two tuyere collectors which are located on opposite sides of the converter. Collector pipes vary in diameter with distance from the connection to air supplying trunk; this is to provide equal pressure of air in each tuyere.
Smelting
Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...
processes. The most commercially important use of the term is in the treatment of molten metal sulfides to produce crude metal and slag, as in the case of copper and nickel converting. Another, now uncommon, use of the term referred to batch treatment of pig iron to produce steel by the Bessemer process. The vessel used was called the Bessemer converter.
Converting in copper metallurgy
A mixture of copper and iron sulfides referred to as matteMatte
Matte may refer to:In film:* Matte , filmmaking and video production technology* Matte painting, a process of creating sets used in film and video* Matte box, a camera accessory for controlling lens glare...
is treated in converters to oxidize iron in the first stage, and oxidize copper in the second stage. In the first stage oxygen enriched air is blown through the tuyere
Tuyere
A tuyere, also can be spelled as tuyère, is a tube, nozzle or pipe through which air is blown into a furnace or hearth.Air or oxygen is injected into a hearth under pressure from bellows or a blast engine or other devices...
s to partially convert metal sulfides to oxides:
- FeS + O2 → FeO + SO2
- CuS + O2 → CuO + SO2
Since iron has greater affinity to oxygen, the produced copper oxide reacts with the remaining iron sulfide:
- CuO + FeS → CuS + FeO
The bulk of the copper oxide is turned back into the form of sulfide. In order to separate the obtained iron oxide, flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...
(mainly silica) is added into the converter. Silica reacts with iron oxide to produce a light slag
Slag
Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and metal atoms in the elemental form...
phase, which is poured off through the hood when the converter is tilted around the rotation axis:
- 2 FeO + SiO2 → Fe2SiO4 (sometimes denoted as 2FeO•SiO2, fayaliteFayaliteFayalite is the iron-rich end-member of the olivine solid-solution series. In common with all minerals in the olivine group, fayalite crystallizes in the orthorhombic system with cell parameters a 4.82 Å, b 10.48 Å and c Å 6.09.Iron rich olivine is a relatively common constituent of acidic and...
)
After the first portion of slag is poured off the converter, a new portion of matte is added, and the converting operation is repeated many times until the converter is filled with the purified copper sulfide. The converter slag is usually recycled to the smelting stage due to the high content of copper in this by-product. Converter gas contains more than 10% of sulfur dioxide, which is usually captured for the production of sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
.
The second stage of converting is aimed at oxidizing the copper sulfide phase (purified in the first stage), and produces blister copper. The following reaction takes place in the converter:
- CuS + O2 → Cu + SO2
Copper content in the obtained blister copper is typically more than 95%. Blister copper is the final product of converting.
Equipment
The converting process occurs in a converter. Two kinds of converters are widely used: horizontal and vertical.Horizontal converters of the Pierce-Smith type prevail in the metallurgy
Metallurgy
Metallurgy is a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys. It is also the technology of metals: the way in which science is applied to their practical use...
of non ferrous metals. Such a converter is a horizontal barrel lined with refractory material inside. A hood for the purpose of the loading/unloading operations is located on the upper side of the converter. Two belts of tuyeres come along the axis on either sides of the converter.
Molten sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
material, referred to as matte
Matte
Matte may refer to:In film:* Matte , filmmaking and video production technology* Matte painting, a process of creating sets used in film and video* Matte box, a camera accessory for controlling lens glare...
, is poured through the hood into the converter during the operation of loading. Air is distributed to tuyeres from the two tuyere collectors which are located on opposite sides of the converter. Collector pipes vary in diameter with distance from the connection to air supplying trunk; this is to provide equal pressure of air in each tuyere.