Question

In extractive metallurgy of zinc, partial fusion of ZnO with coke is called ______ and reduction of the ore to molten metal is called ______ (smelting, calcining, roasting, sintering).
1. Roasting; calcining
2. Roasting; smelting
3. Sintering; smelting
4. Sintering; calcining

Answer 1

Hint: Here, we need to recall the steps of extraction of crude metals from concentrated ore which include: Conversion of the concentrated ore to its oxide form and conversion of oxide to metallic form.

Complete step by step answer:
The heat treatment process in which a large quantity of the loose aggregate material is subjected to sufficiently high pressure and temperature that causes loose material to become a compact solid piece is called sintering. The amount of heat and pressure is slightly less than the material's melting point during the sintering process.
In case of zinc, the extraction is mainly done from its sulphide ore which is zinc blende (ZnS), which is first converted to ZnO by the process of roasting which occurs at 1200K. Roasting is the process of heating the ore below its melting point with excess of air.
$2ZnS{\text{ + 3}}{{\text{O}}_2}{\text{ }} \to {\text{ 2ZnO + 2S}}{{\text{O}}_2}$
The next step is the process of reduction which in case of zinc is done with carbon or coke as a reducing agent. The entire process of reduction is called smelting which is done in a blast furnace.
In the blast furnace a charge of sintered zinc oxide and preheated coke is added. A blast of hot air through tuyeres provides oxygen to burn coke for heat and to supply carbon monoxide reducing gas. The zinc that is reduced passes out of a furnace as vapour, and this is drawn off to the spray bath of molten lead and condensed to liquid zinc metal.
$ZnO{\text{ + C }}\xrightarrow{{1676{\text{ K}}}}{\text{ Zn + CO}}$
The correct answer is option 3. In extractive metallurgy of zinc, partial fusion of ZnO with coke is called sintering and reduction of the ore to molten metal is called smelting.

Note:
The whole process of smelting is done for the extraction of metals present in the middle of reactivity series i.e. zinc, copper, iron, lead.