[Chemistry Class Notes] Ores and Minerals Pdf for Exam

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.

1. Gravity Separation – This method is based on the difference in the gravities of ore and gangue particles.

2. 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.

3. 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.

4. 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 –

1. 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  :

1. Primary Crushing 

2. Secondary Crushing 

3. 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 –

1. 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.

2. Roasting – Roasting is a process in which ore is roasted to temperatures below its melting points, usually in the presence of air.

3. 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

1. Group 1st element is called Alkali metals because its hydroxides are alkaline whereas group 2nd elements are called Alkaline earth metals.

2. Silver and copper are the best conductors of electricity.

3. Osmium is the heaviest metal and Platinum is the hardest.

4. Gold and Silver are the most malleable metals.