ORE, ORE MINERALS, AND GANGUE

Elements In Nature

Earth’s crust contains many elements in pure or combined states. There are 118 elements in the periodic table. Out of these elements, 95 are metals. Aluminium is the most abundant metal of earth’s crust and Iron is the second most abundant. 

The percentage of different elements in the earth’s crust are-Oxygen-49%, Silicon-26%, Aluminium-7.5%, Iron-4.2%, Calcium-3.2%, Sodium-2.4%, Potassium-2.3%, Magnesium-2.3%, Hydrogen-1%.

Metals occur in 2 forms in nature depending upon their chemical reactivities:

• Native State: Elements that have low chemical reactivity or noble metals having the least electropositive character are not attacked by Oxygen, moisture, and Carbon Dioxide. These elements, therefore, occur in the free state or in the native state, e.g. Gold, Silver, Platinum, Sulphur, Oxygen, Nitrogen, noble gases, etc.

• Combined State: Elements that are highly reactive and are readily attacked by moisture, Oxygen, and Carbon Dioxide. These elements occur in nature in combined form as their compounds such as Oxides, Carbonates, Sulphides, Halides, etc. Examples-Fluorine, Chlorine, Sodium, Potassium, etc. Hydrogen is the only non-metal that exists in oxidised form only.

Minerals

Minerals are naturally occurring substances in the earth’s crust along with impurities. They are solid chemical compounds with well-defined chemical compositions and specific crystal structures that occur naturally in pure form. Living beings often synthesise inorganic minerals that are found in rocks. 

Physical Properties of Minerals 

• Hardness: Resistance to scratching.
• Colour: Caused by electromagnetic radiation interaction with electrons.
• Lustre: Reflection of light from the mineral surface.
• Specific Gravity: Density of mineral.
• Radioactivity- Property of emitting energy and subatomic particles simultaneously.
• Magnetism: Behaviour with magnets.
• Fluorescence: Emission of electromagnetic radiation.
• Streak: Colour of the mineral in powdered form.
• Tenacity:  Resistance to breaking.
• Diaphaneity: The ability of light to pass through the mineral.
• Cleavage: How cleanly and easily mineral breaks.
• Fracture: When a mineral is broken in a direction that does not correspond to a plane of cleavage.
• Reaction to acid: Used to distinguish carbonates from other minerals.
  
  

Minerals are classified by chemical constituents. The 2 important systems of classification are-

• Dana Classification: This is the most commonly used system. In 1848, Professor James Dana of Yale University designed this system. The Dana system divides minerals into eight basic classes. The classes are-

• Native Elements: In this category, the elements are found in a pure state.
• Silicates:  Silicates are made from metals combined with silicon and Oxygen.
• Oxides: Oxides formed by the combination of metal with Oxygen.
• Sulfides: Compounds made from Sulphur combined with metal.
• Sulfates: Compounds made from Sulphur combined with metal and Oxygen.
• Halides: They form from Halogen elements like Chlorine, Bromine, Fluorine, and Iodine combined with metals.
• Carbonates: This group of minerals is made of Carbon, Oxygen, and Metals.
• Phosphates: They are not as common in occurrence. They are often formed when other minerals are broken down by weathering.
• Mineraloids: These substances do not fit neatly into the above-mentioned eight classes. For example-Opal, Jet, Amber, and the mother of Pearl.

• Strunz Classification: This system was introduced by the German mineralogist Karl Hugo Strunz in 1941. It was based on the chemical structural classification of the entire domain of minerals. In this system, minerals are divided into 10 major composition classes: Elements, Sulphides, Halides, Oxides, Nitrates and Carbonates, Borates, Sulphates, Phosphates, Silicates, and Organic Compounds.

 ORES

Ores are the minerals from which metals can be conveniently and economically extracted. All ores are minerals but all minerals are not ores. Ores are extracted from the earth’s crust through mining and then are treated or refined, often by the process of Smelting(the process of extraction of metal by fusion of its oxide ore with carbon) or Calcination(the process of converting an ore into its oxides by heating it strongly, below its melting point in a limited supply of air) to extract the valuable metals or minerals.

Active metals occur in the form of the following categories of ores-

 Metallurgy: The scientific and technological process carried out for isolating the metal from its ores is known as metallurgy.

Terms involved in the extraction of metals

• Flux: The substance added to convert infusible mass into some fusible mass is called flux.

Infusible mass + flux    Fusible mass(slag)

Depending upon the nature of impurity, flux may be acidic or basic.

• Acidic Flux: It is used to remove basic impurities. e.g., Silica, Boron Trioxide, Phosphorus Pentoxide etc., are acidic flux.
• Basic Flux: It is used to remove acidic impurities e.g., Lime, Limestone, Magnesia, etc., are basic flux.

• Slag: The fusible mass obtained by the reaction of flux and infusible mass is called slag and this process is called slagging operation.

• GANGUE OR MATRIX: The impurities associated with ores are called gangue or matrix.
  
  

Types of Metallurgy

• Pyrometallurgy: This type of metallurgy is used to extract the elements by thermal treatment. The metals extracted from this metallurgy are Copper, Iron, Zinc, Tin, etc.

• Hydrometallurgy: This method is used to extract metals from their aqueous solutions. Silver and gold are extracted by this method.

• Electrometallurgy: In this method, electrolysis is used in the extraction of metals. Sodium, Potassium Lithium, Calcium, etc., are extracted from their molten salt solution through the electrolytic method. 

Conclusion

Minerals and ores are sources of metals that are extracted from the earth’s crust. Minerals from which metals can be extracted are called ore. Metallurgy is used to extract metals from these ores. Metallurgy includes several steps from the concentration of the ore to purification. After purification, these metals are used for many purposes like alloy making, electrical wire making, paints, coatings, etc.