Question

Heating of ore in absence of air below its melting point is called
(A) Leaching
(B) Roasting
(C) Smelting
(D) Calcination

Answer 1

Hint: The answer to the above question is a method which is widely used in the industrial processes as a part of the purification process.

Step by step answer:
> Calcination is commonly used to convert hydrated oxides or hydroxides and carbonates into respective oxides. It involves heating of the ore below its fusion temperature in absence of air. This step is generally performed in a reverberatory furnace. The concentrated ore is put on the hearth of the furnace and heated by flames deflected from the roof. Example of Calcination process is:
$ZnC{{O}_{3}}\xrightarrow{{}}ZnO+C{{O}_{2}}$
Therefore, we can say that Option D is the correct answer.

> Leaching is a chemical separation. It involves the treatment of the ore with a suitable reagent to make it soluble while impurities remain insoluble. The insoluble impurities are separated by filtration. The impurities, in this case, include not only gangue but also chemical entities which are not solubilized during leaching operation.

> Roasting is a process in which the ore is heated in presence of air. During this operation, the temperature is kept below the melting point of the ore. The sulphide ores are generally subjected to roasting. The roasting is generally done in a reverberatory furnace or in a small blast furnace. As a result of roasting, the following changes occur. (i) Moisture is driven out. (ii) Organic matter is burnt. (iii) The non-metallic impurities such as sulphur, phosphorus, arsenic are converted into respective volatile oxides which get removed. Example of the roasting process is:
$2ZnS+3{{O}_{2}}\xrightarrow{{}}2ZnO+2S{{O}_{2}}$

> Smelting is a process of applying heat to ore in order to extract the base metal. It is a form of extractive metallurgy. This involves reduction of ore to the molten metal at a high temperature. For the extraction of less electropositive metals such as Pb, Zn, Fe, Sn, etc., powerful reducing agents such as C, CO, water gas, Na, K, Mg, Al may be used.

Note: The main purpose for performing the Calcination process for heating the solids to high temperature is to remove the volatile substances, oxidizing a portion of mass, or rendering them friable.