Learn How the Extraction of Metals from Ores is Done
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
1. What is metallurgy?
Metallurgy is the scientific and technological field that deals with the extraction of metals from their natural sources, called ores. It covers the entire process, from mining and concentrating the ore to extracting the metal and finally purifying it to a usable form. It also includes the study of the physical and chemical properties of metals and the creation of alloys.
2. What are the main steps involved in extracting a metal from its ore?
The extraction of metals from ores generally follows three major steps:
- Concentration of the Ore: This step involves removing impurities (like sand, soil, and rock), collectively known as gangue, from the ore. This is also called ore dressing or enrichment.
- Isolation of the Metal from its Concentrated Ore: The concentrated ore is converted into a form that is suitable for reduction, typically a metal oxide. The metal oxide is then reduced to obtain the crude metal.
- Refining or Purification of the Metal: The extracted metal, known as crude metal, contains impurities. Refining is the process of removing these impurities to obtain the pure metal.
3. Why is it necessary to concentrate an ore before extracting the metal?
It is necessary to concentrate an ore to remove the earthly and rocky impurities, known as gangue. If the gangue is not removed, the subsequent extraction process would be highly inefficient and uneconomical. Concentrating the ore increases the percentage of the desired metal, making the heating and reduction processes more effective and requiring less energy and fewer chemical reagents.
4. What is the difference between calcination and roasting?
Calcination and roasting are both processes used to convert concentrated ores into metal oxides by heating them, but they differ in the presence of air.
- Calcination is the process of heating an ore, typically a carbonate or hydrated ore, strongly in the absence or limited supply of air. This drives off volatile matter like carbon dioxide (from carbonates) or water (from hydrated ores). For example, Zinc Carbonate (ZnCO₃) is calcined to Zinc Oxide (ZnO).
- Roasting is the process of heating an ore, usually a sulphide ore, in the presence of excess air below its melting point. This converts the sulphide ore into a metal oxide. For example, Zinc Sulphide (ZnS) is roasted to form Zinc Oxide (ZnO).
5. How are metals extracted from their concentrated ores based on their reactivity?
The method used for extracting a metal depends on its position in the reactivity series.
- High Reactivity Metals (e.g., Na, K, Al): These metals are very reactive and cannot be reduced by common reducing agents like carbon. They are extracted using electrolysis of their molten salts.
- Medium Reactivity Metals (e.g., Zn, Fe, Pb): These metals are moderately reactive. Their oxides are typically reduced to the metal using a chemical reducing agent like carbon (coke) in a blast furnace.
- Low Reactivity Metals (e.g., Hg, Cu, Ag): These metals are the least reactive. Their sulphide ores can often be converted to metal simply by heating in air (roasting).
6. What is the importance of refining metals, and what is a common method used?
The metal obtained after reduction is often impure and is called crude metal. Refining is crucial to remove these impurities, as they can negatively affect the metal's properties, such as its strength, conductivity, and resistance to corrosion. A very common and effective method for refining many metals, like copper and zinc, is electrolytic refining. In this process, the impure metal is made the anode, a strip of pure metal is the cathode, and a salt solution of the metal is the electrolyte. On passing an electric current, pure metal from the anode dissolves and deposits onto the cathode.
7. Why is carbon (coke) used as a reducing agent for many metal oxides but not for all?
Carbon, in the form of coke, is a widely used reducing agent because it is inexpensive and effective for metals in the middle of the reactivity series, like iron and zinc. However, it cannot be used for all metal oxides. Highly reactive metals like aluminium and sodium form very stable oxides because they have a stronger affinity for oxygen than carbon does. This means carbon is not a strong enough reducing agent to displace them from their oxides. For these metals, the more powerful method of electrolytic reduction is required.
8. What is the role of a flux in metallurgical processes and how does it work?
A flux is a chemical substance added during smelting to combine with impurities (the gangue) to form a fusible compound called slag. The gangue is often a high-melting-point oxide. The flux is chosen based on the chemical nature of the gangue. If the gangue is acidic (like silica, SiO₂), a basic flux (like limestone, CaCO₃) is added. The flux reacts with the gangue to form slag, which is molten at the furnace temperature. Since the slag is lighter than the molten metal, it floats on top and can be easily removed, thus purifying the metal.
9. How does the principle of electrolysis apply to the extraction of highly reactive metals like Sodium or Aluminium?
Highly reactive metals like Sodium and Aluminium have a very strong attraction to the non-metals they are bonded with in their ores. This bond is too strong to be broken by chemical reducing agents like carbon. Electrolysis uses electrical energy to force this chemical separation. The metal's molten salt or oxide is used as the electrolyte. When a direct current is passed through it, the positive metal ions are attracted to the negative electrode (cathode), where they gain electrons and are deposited as the pure liquid metal.
10. Why are most metals found as compounds (ores) in nature and not in their pure form?
Most metals are chemically reactive and tend to combine with other elements in the environment, such as oxygen and sulphur, over geological time. This reaction forms more stable compounds, which we call minerals or ores. Only the least reactive metals, like gold and platinum, have such a low tendency to react that they can be found in their pure, elemental state in nature. The more reactive a metal is, the more readily it forms these stable compounds.
