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Metallurgy is the branch of science concerned with the extraction of metals from naturally occurring ores. Most elements, such as metals, exist in a combined state with other elements, and these are referred to as minerals. Although an element can combine with a variety of other elements to form various minerals, only a few of them are good sources of that metal. Ores are such sources, and mining is the process of extracting metal ores buried deep underground. Metal ores can be found in abundance in the earth’s crust. Metal extraction from ores aids in the utilization of minerals found in the ground. In fact, Zinc (Zn) is a metallic element with a hexagonal close-packed (hcp) crystal structure that has a density of 7.13 grammes per cubic centimetre. It has a moderate hardness and can be made ductile and easily worked at slightly higher temperatures than the ambient. It is greyish white in solid form due to the formation of an oxide film on its surface, but it has a bright, silvery appearance when freshly cast or cut. Its most important application, as a protective coating for iron known as galvanising, stems from two outstanding properties: it is highly resistant to corrosion and, when in contact with iron, provides sacrificial protection by corroding in place of the iron.
Overview
Zinc ores are regained using a variety of mining techniques, ranging from open-pit mining (mostly in the case of oxidised ore bodies found closer to the Earth’s surface) to traditional underground methods (used for the more deeply located sulphide ores). Cut-and-fill stopping is the most common underground method of ore extraction, in which tunnels are dug to moderate depths and branch away from mine portals.
Because of the small fraction of zinc sulphide minerals present in the ore, beneficiation is required to produce a concentrate suitable for treatment. The most common method for achieving this concentration is flotation separation, which separates the sulphide mineral from the impure constituents, or gangue. The ore is first crushed to about 1.9 centimetres (0.75 inch), then combined with water and ground to less than 0.1 millimetre in a ball mill. The finely ground particles and water combine to form a slurry, which flows from the mill to flotation cells or tanks, where it is agitated by beaters in the action of selected chemical reagents that create a suspension of air bubbles. The granules cling to the bubbles and float to the surface, forming an oily froth that is constantly skimmed, whereas the gangue is wetted by the chemical action and sinks in the cell. The proper selection of frothing agents allows for the concentrated separation of each constituent mineral of complex lead and zinc sulphides.
Concentrates are roasted in fluidized-bed roasters, which suspend finely divided and heated concentrate particles in a rising stream of air, for electrolytic production of zinc. The sulphur content can be reduced to less than 0.5 percent, and the resulting high-strength (10 percent) sulphur dioxide gas is sent to a sulfuric acid plant. The process is thermally efficient, and the calcine produced is in the form of small particles that can be easily leached into solution for further processing.
Extraction of zinc from its ore
Generally, Zinc processing entails extracting zinc from its ores and preparing zinc metal or chemical compounds for use in a variety of products. Although zinc ores are found all over the world, North America and Australia produce more than 40% of the world’s output. The far more common zinc-containing minerals are zinc sulphide zinc blende or sphalerite (ZnS), a ferrous form of zinc blende known as marmatite [(ZnFe)S], and a zinc carbonate known as calamine or smithsonite (ZnCO3).
Extraction of zinc from zinc blende
Zinc Blende, also known as Zinc Sulphide, is the most commonly available ore used in zinc extraction (ZnS). Zinc extraction has historically been more difficult than the extraction of other metals because zinc is a gas at temperatures where metals such as iron typically begin to melt. Zinc will escape with exhaust gases at such temperatures due to its extremely low boiling point. Because Zinc-Blende contains a low percentage of zinc, it must be concentrated. Froth flotation is the most effective method of concentration for zinc ore.
The froth flotation process is primarily used to separate gangue from sulphide ores. The ore is ground into a fine powder, and a water suspension is formed. Collectors and Froth Stabilizers are the two main components of froth flotation. Collectors (pine oils, fatty acids, etc.) increase the wettability of the ore’s metal component, allowing it to form a froth, and Froth Stabilizers (cresols, aniline, etc.) keep the froth in place. The metal is lubricated by the oil, while the gangue is lubricated by the water. The froth is made by continuously stirring the suspension with paddles and air. The frothy metal is skimmed off the top and dried to recover the metal.
Roasting is the next step in the extraction of zinc. The concentrated ore is finely ground into small pieces before being suspended in an ascending stream of air. With this method, the sulphur content can be drastically reduced. This also converts the Zinc Blende to ZnO, a much more reactive metal.
Extraction of zinc from zinc oxide:
In the Belgian Process, zinc oxide is mixed with coke and ground into fine pieces before being heated at 1673 K in fire clay containers. Zinc Oxide is reduced to metallic Zinc at this point. In this reaction, the carbon from coke acts as a reducing agent.
Coke is being used in the reduction of zinc oxide. In this case, the temperature is higher than in the case of copper. The oxide is formed into briquettes with coke and clay for heating purposes.
ZnO + C àZn + CO (Here, coke is the catalyst, and temperature is 673 K)
By rapidly chilling, the metal is distilled off and collected.
Because the boiling point of zinc is 1180 K, the zinc formed immediately vaporises and distils over, leaving non-volatile impurities such as Cadmium, Lead, and Iron behind. This gas, which contains zinc vapours, is collected and cooled to produce solid zinc. Spelter is the name given to this raw metal. To even further purify it, fractional distillation can be used.
Zinc alloys with either a metal like nickel silver, bronze, brass, and soft electrical solder. A large portion of the zinc produced is used to galvanise iron to prevent corrosion.
The information about the principles of extraction of zinc from various chemistry-related articles are available here. Generally, Zinc processing entails extracting zinc from its ores and preparing zinc metal or chemical compounds for use in a variety of products. Students who want to flourish in chemistry need to be well known about this to get deep knowledge about it to do well on their exams. The principle and steps in zinc extraction is provided here to assist students in effectively understanding the respective topic. Continue to visit our website for additional chemistry help.
FAQ’s
How is zinc extracted from zinc blende?
Zinc from zinc blende is produced by roasting zinc first. Following roasting, a reduction process in the presence of carbon is carried out, resulting in the formation of free metal, which is zinc.
Which metal is extracted by hydrometallurgy?
Hydrometallurgy produces a large amount of copper and zinc, in addition to most gold and silver.
What is the use of zinc?
Zinc is indeed a nutrient found throughout your body that helps your immune system and metabolism function properly. Zinc is also necessary for wound healing and for your senses of taste and smell. A varied diet usually provides enough zinc for your body. Chicken, red meat, and fortified breakfast cereals are examples of zinc-rich foods.
