Metals form an indispensable part of human life. In today’s age, no aspect of our world remains untouched from metals. We use metals to make utensils, vehicles, medicine, etc. Metals do not occur in nature in their pure form. They need to be extracted from their ores to make them fit for human consumption. This is where we need metallurgy.
Metallurgy is the science that deals with the reduction, oxidation, and extraction of metals from their ores. Metallurgy is the branch of chemistry that helps us know the properties of metals and assists in their production. Metals mixed with sand, limestone, and rocks are present in nature and this mixture is known as minerals.
Minerals that contain the amount of metal that can be extracted economically are used by us. A substance called flux is added to the furnace to remove the impurities present in the metal ore. During this process, the impurities that are removed from the mixture are called gangue. Once the gangue is removed from the metal ore using flux, we get the metal in its pure form. This extracted metal is then used in industries for various purposes.
PRINCIPLES OF METALLURGY
The process of metallurgy is carried out in certain steps. These steps are also called the principles of metallurgy. Let us take a detailed look at these principles below:
CRUSHING AND GRINDING
The first step in the extraction of metals from their ores involves the crushing of the ore into a fine powder. This process is known as pulverization.
THE CONCENTRATION OF ORES
The ores of metals contain gangue (impurities) which reduces the concentration of metal in the powder we get after pulverization. The removal of unwanted gangue from this powder is called dressing of the ore. The process of dressing is also known as the concentration of the ore as the percentage of metal is moderately increased after the dressing of the ore.
There are two ways in which the concentration of the ore is achieved. These methods are as follows:
- Hand Picking - in this method, the rock is separated from the metal through hand picking with the use of a hammer. It is a traditional method that uses manpower for the process of dressing the ore.
- Hydraulic Washing - In this method, water is used to separate the heavier metals from the lightweight gangue. An upward stream of water is used to wash the crushed ore. The gangue is washed away with water and pure metal remains once the process is complete.
- Magnetic Separation - In this process, the crushed ore is put on a conveyor which passes through a magnetic field. The magnet attracts either the gangue or the metal, separating the two. If either the gangue or the metal is capable of being attracted to a magnet, this method can be used.
- Froth Flotation - The process of froth flotation is carried out by mixing the powdered ore in water and creating a suspension. Collectors or froth stabilizers are added to this suspension and then air is drawn in it with the help of a rotating paddle. This agitates the mixture and froth is created. This froth is then dried out and what remains behind is the metal. Froth flotation can be used for sulphide ores of metals like copper, lead, and zinc.
- Leaching - This process is used to separate the gangue from the metal using a chemical. If the powdered ore is soluble in a suitable solvent, it is mixed with that liquid and a reagent is added. The chemical reaction that takes place with the addition of the reagent separates the gangue and metal remains dissolved in the liquid. The resulting liquid is then filtered to remove the gangue and obtain pure metal.
Once the powdered ore is concentrated, it is heated in the presence of excess oxygen at a temperature below the melting point of the metal. This process is called roasting. It is usually carried out for sulphide ores. During roasting, sulphides are temporarily converted to oxides and volatile impurities are removed. The elemental/pure form of sulphur, arsenic, and antimony are extracted.
The process of heating a concentrated ore in the absence of air in order to melt the ore is called calcination. It is carried out for carbonated ores.
Roasting and Calcination are carried out in a reverberatory furnace. During roasting, air holes of the furnace are kept completely open while calcination is performed with the air holes partially or completely closed.
Metallurgy is a very interesting aspect of science and technology. Scientists all over the world are working towards making metallurgy sustainable and affordable. The future looks bright with such research going on in the field of metallurgy. For more such