Question

Define calcination and roasting. Give one example of each.

Answer 1

Hint:These two processes are used in metallurgy. These are a specific treatment provided to the metal ores in order to get a particular resultant product.One of them is used for converting carbonates and hydroxides to their oxides and another is used for converting sulphide ores into their oxides.

Complete step by step answer:
We will first discuss calcination:
Calcination: According to the definition given by IUPAC, calcination is “heating to high temperatures in presence of air or oxygen”. Calcination is also described as the process of thermal treatment applied to ores of metal or other solid materials to bring a thermal decomposition, in a limited supply of oxygen.
The most common application of calcination is decomposition of calcium carbonate to calcium oxide and carbon dioxide for the preparation of cement.
     \[CaC{{O}_{3}}\to CaO+C{{O}_{2}}(g)\]
Calcination is generally provided to a metal ore in order to remove the impurities like carbon dioxide or sulphur dioxide from the ores.
Now, moving on to roasting-
Roasting: It is a process of heating of sulphide ores at a very high temperature with excess supply of oxygen or air.
This process of often applicable for sulphide minerals where the sulphide is converted to an oxide and sulphur is released as sulphur dioxide. The most common example of roasting is for the zinc-sulphide ore, sphalerite (ZnS)-
     \[2ZnS+3{{O}_{2}}\to 2ZnO+2S{{O}_{2}}\]
As a result of roasting, the moisture retained in the ores due to previous purifications processes escapes and due to the excess oxygen the impurities like sulphur, arsenic and phosphorous are converted into their gaseous oxides-
     \[\begin{align}
  & S+{{O}_{2}}\to S{{O}_{2}}\uparrow \\
 & 4P+5{{O}_{2}}\to 2{{P}_{2}}{{O}_{5}}\uparrow \\
 & 4As+3{{O}_{2}}\to 2A{{s}_{2}}{{O}_{3}}\uparrow \\
\end{align}\]
(The upward arrow demonstrates evolution of gas)

Note: It is important to remember that calcination is an oxygen deficient process and roasting is an oxygen excess process. However, they are used for the same purpose i.e. purification of the metal ore.
It is also important to remember that calcination should not be confused with calcification which is a completely different term. Calcination is derived from the Latin word which interprets ‘burning of lime’