Question

Define roasting and calculation? Why these two are necessary during extraction of metals?

Answer 1

Calcination :In this process the concentrated ore is heated in the absence of air to a temperature below the melting points of metal. Calcination is done in a reverberatory furnace. In Calcination,
a. Volatile orgainc matter is driven off.
b. Moisture present on the ore is expelled
c. The ore becomes porous
d. Water is removed from the hydrated oxides ores.

Al2O3.2H2O (bauxite) → (clacination) Al2O3 + 2H2O↑

Fe2O3.3H2O ( Limonite )→ (calcination) Fe2O3 + 3H2O↑
e. Carbonate ores are decomposed to their oxides
ZnCO3 (Zincite)→ ZnO + CO2↑
MgCO3 (Magnesite)→ MgO + CO2↑
CaCO3 (limestone)→ CaO + CO2↑RoastingIn this process , the ore is heated alone or mixed with other materials under regular supply of air at a temperature below the melting point of the metal. Roasting is usually applied to sulphide ore. During roasting
a. Moisture is driven away
b.Volatile impurities are removed
c. Organic matter is destroyed
d. Sulphur, arsenic and other volatile substance present in the free or combined states are oxidized to volatile oxides.
2Zns + 3O2 → 2ZnO + 2SO2↑
4FeS2 + 11O2 → 2Fe2O3 + 8SO2↑
2HgS + 3O2→ 2HgO + 2SO2↑
Sometimes ore is mixed with suitable material and then subjected to roasting in the absence of air,
Ag2S + 2NaCl → 2AgCl + Na2S
AgCl + 2Hg → AgHg + HgCl
Roasting is generally carried out in a reverberation furnace or in a blast furnace.

Answer 2

The carbonate ores are changed inti oxides by heating strongly in limited air is kniwn as calcination.
The sulphide otes are converted into oxides by geating strongly in the presence if excess air is callsd roasting.
These are necessary during extraction because these processes help in getting the pure metal from its impure metal to make new items .
Hope this helps u