Enrichment of Ore: An Introduction
Earth’s crust is full of minerals, which contain elements in their free form or mixed with other elements. The chemical compositions of minerals give them certain uniqueness, they are found on earth concentrated in various forms like rocks and sediments, and these elements are often mixed with other compounds which are considered impurities. These elements, especially metals, are very important for their essential utility in humans and need to be extracted in high concentration.
Ores are such deposits of minerals in high concentration on the earth’s crust from which the pure minerals can be extracted by removing impurities; this removal of impurities from ore is known as enrichment of ores, it is also called concentration of ores.
Concentration of Ores
Concentration of ores is basically the removal of impurities known as gangue particles to increase the percentage concentration of the mineral. This process of removal of impurities from the ore is often referred to as concentration, dressing, or beneficiation of ores. The physical and chemical properties of gangue determine the process of ore enrichment. Various methods of concentration of ore are:
Hand Picking
Hydraulic Washing
Froth Floatation Process
Magnetic Separation
Chemical Separation.
Table: Ores of Some Principal Metals
Methods of Enrichment
Hand Picking – This is a traditional method where the impure solid matrix – identified by their colour – is removed with the help of a hammer.
Hydraulic Washing – In this method, the ore is finely ground and washed with water. The passing water washes away the impurities that are lighter than the mineral. The upstream water passing through the ore takes away the lighter gangue particles leaving behind the heavier metal particles. This is a method of gravity separation. Mainly Tin and Lead oxide ores are separated by this method.
Froth Floatation – Sulphide ores are concentrated by this method. The metal is collected in the form of froth by wetting it in water with the help of collectors and froth stabilisers. Collectors used are pine oils and fatty acids. Froth stabilisers used are cresols and aniline. Collector oil lubricates the metal particles and increases the non-wettability of the ore. The froth stabilisers help the foam float.
The ore is first powdered and mixed in water, the oil is poured into it which wets the metal particles, and the impurities (gauge) are wetted by the water. Stirring the mixture subsequently forms forth which separates the metal from the impurities. Agitating the water allows air to circulate throughout the mixture which helps the metal particles stick with the oil and rise up to the surface as froth. The impurities settle at the bottom, and the froth is collected to extract minerals. Copper, lead, and Zinc sulphide ores are concentrated by this method.
Magnetic Separation - This method is used for ores with magnetic properties. If either the element or the gauge has magnetic properties, they can be separated using a magnetic separator. Mainly the magnetic ore containing iron (magnetite, chromite) or manganese (pyrolusite) is concentrated in this manner. The ore is first finely powdered and put on a conveyor belt; the belt is then passed over a magnetic roller. The magnetic ore stays stuck on the belt, whereas the nonmagnetic gauge slides off.
Chemical Separation - This method involves chemical leaching. The metal and the gauge differ in their chemical reactivity and can be dissolved separately using a particular reagent. The metal can then be concentrated from this solution. Bauxite and silver ores are separated in this manner.
Extraction of highly reactive metals from their ores is performed by electrolysis. Medium reactivity metals can be extracted by Roasting, calcination, and reduction. The least reactive metals can be extracted by roasting and refining. The reactivity of the metal can be ascertained from the activity series and it depends upon its electronic structure.
Uses
Ores are a source of precious metal.
Aluminium is a malleable metal used in a variety of household materials. It is used to make cans, foils, and kitchen utensils.
Copper is a good conductor of electricity. It is used for making electric appliances such as wires, conductors, transformers etc.
Iron is the most important metal on the planet. It is used to make steel alloy.
Key Features
Ores are naturally occurring deposits of mineral like rocks and sediments.
Ores contains a high concentration of minerals that can be extracted profitably.
Natural ores contain impurities called gangue particles mixed with the important mineral.
Removal of impurities and extracting a pure form of the metal is called concentration of ores.
Concentration of ores is also called ore enrichment.
Common methods of enrichment are Hand Picking, Hydraulic Washing, Froth Floatation, Magnetic Separation, and Chemical Separation.
Interesting Facts
Aluminium is the most abundant metal in the world.
Earliest evidence of metallurgy in India is from Mehrgarh, Balochistan. Small copper beads dated around 6000 BCE.
Gold, copper, silver, lead, tin, iron, and mercury are seven metals of antiquity.
FAQs on Enrichment of Ores
1. What is metallurgy?
Metallurgy is the science of the processes that are used to extract the metal in its pure form.
2. What is the difference between mineral and ore?
Mineral is solid with distinct chemical composition with a definite crystal structure. When the mineral is present in a significant concentration such that it can be extracted profitably, it is termed ore.
3. What is Gravity Separation?
Gravity separation is a technique that utilises the variation in specific gravity of the metal in the ore and the gangue particles for separating the two. For example, hydraulic washing.
