Calcination

Calcination refers to thermal treatment of a solid chemical compound, mixed carbonate ores, whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen generally for the purpose of removing impurities or dangerous substances. Calcination is carried out in furnaces or kilns, various designs including shaft furnaces, rotary, hearth kilns.

Oxidation/Reduction

• Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state.
• In redox processes, the reductant gives electrons to the oxidant. Therefore, in the reaction, the reductant or reducing agent loses electrons and is oxidized, and the oxidant or oxidizing agent gains electrons and is reduced. The pair of an oxidizing and reducing agent that is involved in a particular reaction is called a redox pair. The oxidation itself and the reduction alone are each called a half reaction because two half-reactions always occur together to form a whole reaction.
• Oxidation firstly inferred to a reaction with oxygen to form an oxide. Later, the term was expanded to encompass oxygen-like substances that accomplished parallel chemical reactions. Ultimately, the meaning was generalized to include all processes involving the loss of electrons.
• Substances that have the ability to reduce other substances (cause them to gain electrons) are said to be reductive or reducing and are known as, reductants, or reducers. The reductant (reducing agent) transfers electrons to another substance and is itself oxidized. And, because it donates electrons, the reducing agent is also called an electron donor. Firstly, the word reduction originally referred to the loss in weight upon heating a metallic ore such as a metal oxide to extract the metal. In other words, ore was "reduced" to metal.

• Tempering is a process of heat treating, which is used to increase the strength of iron-based alloys. Tempering is usually performed after hardening, to reduce some of the excess hardness. The exact temperature determines the amount of hardness removed and depends on both the specific composition of the alloy.
• Tempering is most often performed on steel that has been heated above its upper critical temperature and then quickly cooled, in a process called quenching, using practises such as immersing the hot steel in water, oil, or compressed air. The quenched steel, being placed in or very near its hardest possible state, is then tempered to incrementally decrease the hardness to a point more suitable for its application.