What are ores and minerals?
Earth’s crust contains some naturally occurring components called minerals in which metal compounds are found. Ores can be said to be those minerals from which metal can be economically and easily extracted. Metals are not always found in the free state. Metals like Potassium, Sodium, Calcium, Magnesium, etc are found in a combined state. From these Metal Compounds, a pure form of metals needs to be extracted. It should be kept in mind that all ores are minerals but all minerals are not ores.
How are ores extracted?
The process of removing metal from the ore is known as Metallurgy. The ore is generally associated with Earthy impurities like Sand, rocks, and limestone Known as Gangue or Matrix. A substance added to ore to remove the impurities is called flux. The combination of gangue with flux in ores forms a fusible material called Slag.
The concentration of ore is the process of eliminating gangue from the ore. Depending on the nature of the procedure, it can be carried out in the following ways.
Gravity Separation - This method is based on the difference in the gravities of ore and gangue particles.
Magnetic Separation - A powdered ore is carried through a conveyor belt that runs over two rollers, one of which is magnetic, in this operation. The magnetic particles are attracted to the magnetic roller and fall down first, followed by the non-magnetic particles.
Froth flotation process - This method is based on the difference in the wetting properties of the ore and the gangue particles.The Froth Flotation method is used exclusively for sulfide ores.
Leaching Method - The powdered Bauxite ore is treated with mud and a concentrated solution of sodium hydroxide. The ore dissolves in sodium hydroxide to form sodium aluminate and silica dissolves to form sodium silicate. The other impurities remain undissolved and are later filtered out. This process is used when the ore particles are soluble in such a solvent in which the gangue particles cannot be dissolved.
Other methods of extracting ores -
Crushing and Grinding - Crushing and grinding are usually carried out in a sequence of operations by which the lump size is reduced step by step. The purpose of this method is to reduce size particles and to release impurities. There are 3 stages of crushing :
Primary Crushing
Secondary Crushing
Tertiary Crushing
Grinding further has 2 stages - Coarse Grinding and Fine Grinding
All the elements have some physical and chemical properties. The most reactive metals are Potassium (k), Sodium (Na), Calcium (Ca), Magnesium (Mg), Aluminum (Al), Iron (Fe), Mercury (Hg), Copper (Cu), Silver (Ag), etc.
Extraction of Ore from highly Reactive Metals -
Calcination - Calcination is a process that involves heating ore in the absence of air in order to remove water from hydrated oxide at temperatures below the melting point.
Roasting - Roasting is a process in which ore is roasted to temperatures below its melting points, usually in the presence of air.
Smelting -Smelting is the process of reducing oxide ore with carbon at a high temperature.
Important metals and their ores
Difference between Ore and Minerals
Minerals are naturally occurring substances of metals present in the earth’s crust called minerals. For eg - Clay is a mineral of Aluminium.
Ores are those minerals that can be used for the extraction of metal easily and profitably. For eg - Bauxite is an ore of Aluminium.
Some Important facts about Metals
Group 1st element is called Alkali metals because its hydroxides are alkaline whereas group 2nd elements are called Alkaline earth metals.
Silver and copper are the best conductors of electricity.
Osmium is the heaviest metal and Platinum is the hardest.
Gold and Silver are the most malleable metals.
FAQs on Ores and Minerals
1. What is the main difference between a mineral and an ore?
A mineral is any naturally occurring substance with a definite chemical structure. An ore, on the other hand, is a specific type of mineral from which a metal can be extracted profitably and conveniently. In simple terms, all ores are minerals, but not all minerals are considered ores because the metal content might be too low to be economically useful.
2. What exactly is metallurgy?
Metallurgy is the complete scientific and technological process used for isolating a pure metal from its ore. It covers everything from mining the ore out of the ground to the final stage of refining it into a pure form. The entire process is designed to be as efficient and cost-effective as possible.
3. Can you give some common examples of ores and the metals they contain?
Certainly. Here are a few important examples of ores you might encounter:
- Bauxite (Al₂O₃·2H₂O) is the primary ore used to extract aluminium.
- Haematite (Fe₂O₃) is one of the most important ores for producing iron.
- Copper Pyrites (CuFeS₂) is a key ore for extracting copper.
- Galena (PbS) is the main natural source of lead.
4. What are the general steps involved in extracting a metal?
The extraction of a metal from its ore typically involves three main stages:
- Concentration of the Ore: The first step is to remove the unwanted earthly impurities, collectively known as gangue.
- Isolation of the Metal: The concentrated ore is then converted into a metal oxide, which is easier to convert into the crude metal.
- Refining of the Metal: The crude metal obtained contains impurities and must be purified to get the final, refined metal.
5. Why can't all minerals be used to extract metals?
We cannot use all minerals to extract metals primarily for economic reasons. A mineral is only classified as an ore if the percentage of the desired metal is high enough to make the extraction process profitable. Many minerals contain metals, but in such small amounts or complex forms that the cost of extraction would be far greater than the value of the metal obtained.
6. How is the 'gangue' or impurity removed from an ore?
Removing the gangue is done during the concentration of the ore, and the method chosen depends on the physical and chemical properties of the ore and the gangue. Common methods include:
- Hydraulic Washing: Uses gravity and water to separate lighter gangue from heavier ore particles.
- Magnetic Separation: Used when either the ore or the gangue has magnetic properties.
- Froth Flotation: A popular method for sulphide ores, where ore particles attach to froth and float, leaving impurities behind.
- Leaching: A chemical process where the ore is dissolved in a specific solvent, leaving the impurities undissolved.
7. What is the difference between roasting and calcination? When is each method used?
Both are heating processes to convert ores into metal oxides, but the key difference is the presence of air.
- Roasting involves heating an ore strongly in the presence of excess air. It is typically used for sulphide ores (e.g., Zinc Blende, ZnS).
- Calcination involves heating an ore in the limited supply or complete absence of air. This method is used for carbonate and hydrated ores (e.g., Calamine, ZnCO₃).
8. In real life, where is a process like electrolytic refining applied?
Electrolytic refining is widely used in industries to produce metals of very high purity. A classic real-world application is the purification of copper. The impure copper is refined to achieve a purity of 99.9% or higher, which is essential for making high-quality electrical wires, circuits, and electronic components where conductivity is critical.
