Steps In Extraction Of Metals From Ores Including Concentration Roasting Calcination Reduction And Refining
Metallurgy is a fascinating chapter of chemistry students like to study. In this chapter, the different types of metals, their ores and different extraction processes are taught. The inorganic reactions used to extract metals from their ores and purified should be elaborately studied so that you can build a strong foundation of metallurgy and progress to the higher concepts later. To make sure you are on the right path, you can refer to this concept page that will help you clear your doubts related to the extraction of metals.
When you reach Class 12, this will become a crucial chapter to study. Your depth in inorganic chemistry will then be tested. Learn how to extract metals that are used in the industries to manufacture different finished goods. You will also learn how the metals are purified using the most efficient methods. Refer to this concept page and find out how ore is treated step by step to collect a particular metal.
Occurrence of Metals
Earth’s crust is the storehouse of metals such as sulphur, silicon. Some of the major metals are also found in seawater such as chloride. They are present in a free state as well as a combined state. For example, gold and platinum are available in a free state whereas calcium and copper are available in combined states. The metals found in the free state are also called noble metals as they show the least amount of chemical reactivity. On the other hand, the metal present in the combined state can easily react. A material that is naturally occurring comprising the metal is known as a mineral. The pure form of mineral from which a metal can be extracted is called the ore.
Types of Ores
Given below are the types of ores with their examples-
Oxide Ores-
In this particular ore, the metals are present in the oxidised form. Obtaining metals from this ore is much easier. For example, Haematite ore ( Iron) and Bauxite ore (Aluminium)
Sulphide Ores-
In this particular ore, the metals are present in the sulphide form. Since it is difficult to extract metals from this ore, they are usually converted to oxides with the process of metallurgy. For example, Zinc Blende ( Zinc) and Lead (Galena)
Carbonate Ores-
In this ore, carbonate ions are present. Since it is difficult to extract metals from these ores, they are also converted to oxide ores first. For example, Calamine (Zinc)
Sulphate Ores-
They are generally found underground and have sulphur ions present in them. For example, Anglesite (Lead)
What is Extraction of Metals?
We all know that the metals exist mostly in the form of salts along with other minerals to form an ore. These impurities should be removed with the help of different inorganic separation techniques. Every step takes us to a purer content of metal in the ore. In this concept page, every process involved in the extraction of metals will be discussed step by step.
The main aim of designing an extraction process is to minimize the cost and gather the purest form of the metal as much as possible. The conventional metal extraction processes will be discussed elaborately on this concept page. The simpler the process, the better and more cost-effective it is for the industries to extract metals from their ores. It all depends on the principles of metallurgy we use to check the inorganic chemical properties of the constituents of an ore. This is how an extraction process is designed. Every constituent is analysed and then the most suitable process of separating it from the rest is chosen. The basic extraction of metals from ores has the following steps.
Grinding and Crushing
The bigger chunks of the ore extracted are crushed and ground in ball mills and crushers. It helps to increase the surface area of the chunks for better chemical actions later. In technical terms, it is called pulverisation.
Concentrating the Ore
This step concentrates the ore by performing the removal of impurities. It is also called ore dressing. This process is quite elaborate and is named according to the equipment or technique used. Let us take a quick look.
Hydrolytic Method:
In this method, the ground ore particles are poured over a vibrating table with a slope or inclination. A water jet is used to flow on the ground particles. The impurities are lighter than the metal-containing ore particles. They wash down while the heavier particles settle down on the grooves of the inclined table. This is generally used when the metal ore is much heavier than the impurities.
Magnetic Separation:
The name of the concentration process is enough to explain. This technique is used to separate the ferromagnetic metal ore from the impurities after pulverizing. The ground ore particles are carried on a conveyor belt with two wheels. One of these wheels is magnetic. The ferromagnetic ore particles will then get attracted and separated from the impurities easily.
Froth Floatation:
This is one of the methods of extraction of metals from ores by using two mediums together. Both oil and water are used to separate impurities. It can only be done when the ore forms froth when compressed air is passed in this medium. The frothed ore collects on the oil section whereas the impurities settle down in the water medium.
Chemical Separation:
One way of concentrating the ore is by chemical separation. For example, the separation of aluminium (Al) from the bauxite ore. This process of separating aluminium from the bauxite ore is also termed Bayer’s Process. Hot NaOH reacts with the bauxite ore which leads to the formation of sodium aluminate which is water-soluble. The solution of sodium aluminate is then diluted with water which when cooled, gives aluminium hydroxide. This is then further washed and filtered to get the pure aluminium oxide called the alumina.
Calcination and Roasting
Once the ore is concentrated using the above methods, it is then either heated in the presence or absence of air. It all depends on the element and its chemical properties. For instance, sulphide ores are heated in the presence of oxygen. It is called roasting. On the other hand, carbonated metal ores are heated in a vaccum for easy extraction of metals. This is called calcination. This is how a concentrated ore is again refined to gather purer metals.
This is a gist of how the extraction of metals ores and minerals is performed based on the physical and chemical properties of the impure ores. This concept page will also describe how metals in the lower part of the activity series can be extracted from their ores.
Major Metal Ores in India
Iron, which is one of the most important and beneficial metals, is extracted from iron ores. Iron ores mines are found in Goa, Karnataka, Orissa.
Aluminium is extracted from Bauxite ore. In India, the most available ore is Bauxite ore. States with Bauxite deposits are Maharashtra, Tamil Nadu and Gujarat.
Tin which is obtained from tinstone can be found in Jharkhand.
Importance of Metals
Metals are extracted from the ores because of their properties. They can be used in different areas and can benefit humankind. Following are the uses of metals in our day-to-day lives.
Metals are useful for the production of vehicles and their parts. This means that metals play an important role in transportation.
Since they are malleable and ductile, they can be hammered to get different shapes and also can be drawn into wires.
Electronic devices such as computers and household devices such as ovens, microwaves are made with the help of metals.
Metals are also used in medicines to cure mental deficiency diseases in humans.
Metals are also used for construction purposes. For example, iron and steel.
FAQs on Extraction Of Metals From Ores and Their Stepwise Metallurgical Process
1. What is extraction of metals from ores?
The extraction of metals from ores is the process of obtaining pure metal from its naturally occurring mineral form through physical and chemical methods. It involves several key steps in metallurgy:
- Concentration (ore dressing) – Removal of gangue (impurities) from the ore.
- Conversion to oxide – By roasting or calcination.
- Reduction – Converting metal oxide to free metal using a reducing agent.
- Refining – Purifying the extracted metal.
2. What are the main steps involved in metallurgy?
The main steps in metallurgy are concentration, roasting or calcination, reduction, and refining. These steps include:
- Concentration of ore – Removing unwanted materials like sand and clay.
- Roasting – Heating sulphide ores in excess air, e.g., 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g).
- Calcination – Heating carbonate ores in limited air, e.g., CaCO3(s) → CaO(s) + CO2(g).
- Reduction – Converting oxide to metal using carbon, CO, or electrolysis.
- Refining – Purification by methods like electrolytic refining.
3. What is the difference between roasting and calcination?
The key difference is that roasting is heating sulphide ores in excess air, while calcination is heating carbonate ores in limited or no air.
- Roasting: Converts sulphide ores to oxides and releases SO2 gas.
Example: 2PbS(s) + 3O2(g) → 2PbO(s) + 2SO2(g) - Calcination: Converts carbonate ores to oxides and releases CO2 gas.
Example: ZnCO3(s) → ZnO(s) + CO2(g)
4. How are metals extracted based on their reactivity series?
Metals are extracted according to their position in the reactivity series, which determines the method of reduction.
- Highly reactive metals (K, Na, Ca, Al) – Extracted by electrolysis of molten salts.
- Moderately reactive metals (Zn, Fe, Pb) – Extracted by reduction with carbon or carbon monoxide.
- Less reactive metals (Cu, Hg, Ag) – Often extracted by heating or simple reduction.
5. How is iron extracted from its ore in a blast furnace?
Iron is extracted from hematite (Fe2O3) in a blast furnace by reduction with carbon monoxide. The main steps are:
- Formation of CO: C(s) + O2(g) → CO2(g)
- CO formation: CO2(g) + C(s) → 2CO(g)
- Reduction of iron ore: Fe2O3(s) + 3CO(g) → 2Fe(l) + 3CO2(g)
6. What is meant by concentration of ore?
The concentration of ore is the process of removing gangue (earthy impurities) to increase the metal content before extraction. Common methods include:
- Gravity separation – Based on density differences.
- Froth flotation – Used for sulphide ores.
- Magnetic separation – For magnetic ores like magnetite.
7. How does electrolytic reduction help in extraction of metals?
Electrolytic reduction extracts highly reactive metals by passing electricity through their molten compounds to reduce metal ions to metal atoms. For example, aluminium is extracted from alumina:
- At cathode: Al3+ + 3e- → Al(l)
- At anode: 2O2- → O2(g) + 4e-
8. What is refining of metals?
The refining of metals is the purification of impure metal obtained after extraction to achieve high purity. One common method is electrolytic refining:
- Impure metal acts as the anode.
- Pure metal sheet acts as the cathode.
- Metal salt solution acts as electrolyte.
At anode: Cu(s) → Cu2+(aq) + 2e-
At cathode: Cu2+(aq) + 2e- → Cu(s)
9. What is slag in the extraction of metals?
Slag is a fusible product formed when a flux reacts with gangue during metal extraction. In the blast furnace:
- Limestone decomposes: CaCO3(s) → CaO(s) + CO2(g)
- Calcium oxide reacts with silica: CaO(s) + SiO2(s) → CaSiO3(l)
10. Why are highly reactive metals extracted by electrolysis?
Highly reactive metals are extracted by electrolysis because they cannot be reduced by common reducing agents like carbon. Metals such as potassium, sodium, calcium, and aluminium have very negative reduction potentials, so:
- Chemical reduction with carbon is not feasible.
- Electrolysis supplies the required electrical energy for reduction.
At cathode: Na+ + e- → Na(l)
