Smelting
Smelting is a crucial metallurgical process used to extract metals from their ores by melting them in specially designed furnaces. This process typically involves pre-processing the ore to remove unwanted materials, known as gangue, before smelting takes place. During smelting, oxygen is removed from metal oxides, allowing the pure metal to be separated from impurities. Various techniques are employed depending on the type of metal being extracted, and common additives are introduced to facilitate the melting and separation process.
One well-known example of smelting is the blast-furnace method, primarily used for producing pig iron from iron ore. In this process, a vertical furnace is charged with iron ore, coke, and a flux, while preheated air is blown in from below, causing chemical reactions that reduce the ore and produce molten iron. The resulting slag, a byproduct formed from impurities and flux, is removed, leaving behind pig iron that can be further processed into steel. Other metals, such as copper, also undergo smelting but may require different furnace designs and treatments to achieve the desired purity. Overall, smelting plays a vital role in the metal production industry, contributing to the creation of essential materials used in various applications.
On this Page
Subject Terms
Smelting
Smelting is a process that frees metals from their ores so that the metals then can be refined and worked into a useful form.
Definition
Smelting is a metallurgical process in which ores are melted in a specially designed furnace in order to extract metals from the ores. Techniques vary, depending on the metal and the ore, but some common principles apply. ore is generally processed before smelting in order to remove gangue (the unwanted rock or mineral aggregates that are mined along with the ore). After processing, the resulting ore concentrate is smelted. During smelting, ore is reduced—that is, oxygen is removed from metal oxides to yield the metal—and impurities are separated from the metal. Additives placed in the smelting furnace along with the ore help the metal to melt and physically separate from the impurities.
Overview
An example of smelting is the blast-furnace process that produces pig iron from iron ore. A blast furnace is a vertical, chimneylike structure made of iron or steel and lined with firebrick, a specialized building material able to withstand high temperatures and extremely corrosive molten mixtures. Preheated compressed air is carried through tuyeres (pipes) into the bottom of the blast furnace from a gas-fired heater. A charge of iron ore, coke, and sand or limestoneflux is introduced through a valve system at the top of the blast furnace. (The flux is added to lower the fusion, or melting, temperature of the metal.) As the charge descends through the shaft of the furnace, the ascending hot air passes through it. The coke, which is almost pure carbon, oxidizes in the hot-air blast to become carbon monoxide. The carbon monoxide reduces the iron ore, removing its oxygen and in the process reverting to carbon dioxide. Waste gases are captured and used to heat additional fresh air for the process. The heat from the reduction reaction causes the mass within the furnace to melt and descend into the lowermost portion of the furnace, called the crucible. The molten iron sinks to the bottom of the crucible. Slag—the waste material that results when flux combines with incombustible impurities from the ore and ash from the coke—floats on top of the iron. The slag is drawn off from a hole in the upper portion of the crucible, while the iron is tapped off from below and channeled into sand molds. Here it hardens to form pig iron, also called cast iron. Pig iron can be converted to steel through the Bessemer process.
Some copper ores can also be treated in a blast furnace, particularly high-grade oxidized ores. When copper sulfide ores are smelted in a blast furnace, however, the resulting product is an impure metallic sulfide called a copper matte. The matte requires further treatment to produce a form of metallic copper fit for electrolytic refining. Likewise, other metal ores can involve different smelting procedures, furnace designs, fluxes, and additives.