Explain what is roasting.

Hint: Roasting is a process in metal production in which ore is used to extract the metal from the impurity. It is an important branch of metallurgy. Nickel is recovered through extractive metallurgy. It is extracted from its ores by conventional roasting and reduction processes that yield a metal of greater than $75\% $ purity.

Complete step by step answer:
-Metallurgy is a process that is used for the extraction of metals to obtain them in their pure form. The compounds of metals mixed with rocks, soil, sand and impurities are referred to as minerals. These minerals are called ores. Metals can be extracted commercially from ores at low cost and minimum effort. Metallurgy involves the process of purification of metals and the formation of alloys.
-Flux is a substance which is added to remove the impurities. The metallurgical process can be understood by the following points:
-The first step is crushing and grinding of ores into a fine powder using a crusher. This is known as pulverisation.
-Impurities can be removed from the ore and this process is called ore dressing or concentration of minerals.
- Concentration of ores is done by many methods, these are hydrolytic methods, magnetic separation, froth floatation and roasting and calcination.
-Roasting is a specific type of reaction which is used in the conversion of zinc ore to zinc metal. Roasting reaction involves sulphide ore to an oxide ore.
- As per definition, the roasting process involves conversion of sulphide ores to oxide ores. In roasting reactions, the sulphide ore of the metal is treated with oxygen. This results in the formation of the corresponding oxide ore, and also releases sulphur dioxide gas. For example, the zinc ore is converted to zinc metal using the Roasting process.
-So, when we consider the case of the conversion of a zinc ore to zinc metal using the process of roasting, then the corresponding sulphide ore of zinc is converted to its oxide ore. The sulphide ore of zinc, ZnS or commonly known as Zinc Blende ore is reacted with oxygen to give zinc oxide and releases sulphur dioxide gas. The chemical reaction for this process is given by:
 \[2ZnS + 3{O_2}\xrightarrow{{roasting}}2ZnO + 2S{O_2}\]
In the case of roasting of sulfide ore done in metallurgy of copper. Due to partial roasting, the copper sulfide becomes copper oxide which further reacts with unreacted copper sulfide and gives auto reduction. The reaction is shown below.
 \[2C{u_2}S{\text{ }} + {\text{ }}3{O_2}\; \to {\text{ }}2C{u_2}O{\text{ }} + {\text{ }}S{O_2}\] , \[2C{u_2}O{\text{ }} + {\text{ }}C{u_2}S\; \to {\text{ }}6Cu{\text{ }} + {\text{ }}S{O_2}\].

Note:
Mond process is a technique to extract and purify nickel. Carbon monoxide complexes with nickel readily and reversibly to give nickel carbonyl. The steps are listed below:
Firstly, impure nickel is reacted with excess carbon monoxide at ${60^ \circ }C - {80^ \circ }C$ to form nickel carbonyl gas. (Leaving the impurities as solids)
Impure nickel +$CO$ $\xrightarrow{{60 - {{80}^ \circ }c}}Ni{(CO)_4}\xrightarrow{{{{180}^ \circ }C}}Ni + 4CO$
After that the mixture of excess of carbon monoxide and nickel is heated to ${180^ \circ }C$.
On heating, Nickel tetracarbonyl decomposes to give nickel.