Chemistry · Science General

Metallurgical Processes

1,403 Questions

This section explores key metallurgical processes including ore concentration, pyrometallurgy, and metal refining. It also covers corrosion and the properties of refractory materials. These chemistry questions are relevant for engineering and science entrance tests.

Pyrometallurgy furnacesMetal refining techniquesCorrosion protection methodsOre concentrationAuto reduction process

Metallurgical Processes Questions

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

The constituents of the electrolyte for the extraction of aluminium is ____________.

  1. 40 parts cryolite + 40 parts fluorspar + 20 parts pure $Al _2O _3$
  2. 60 parts cryolite + 30 parts fluorspar + 10 parts pure $Al _2O _3$
  3. 30 parts cryolite + 30 parts fluorspar + 40 parts pure $Al _2O _3$
  4. 60 parts cryolite + 20 parts fluorspar + 20 parts pure $Al _2O _3$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Pure alumina melts at about $2000^oC$ and is a bad conductor of electricity. If fused cryoliteand fluorspar is added, the mixture melts at $900^oC$ and $Al _2O _3$ becomes a good conductorof electricity.
Electrolyte: 60 parts cryolite + 20 parts fluorspar + 20 parts pure  $Al _2O _3$

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

A layer of coke is spread over bayzite during extraction of aluminium. This acts as an ____________.

  1. flux

  2. slag to remove impurities

  3. reducing agent

  4. insulation and does not allow heat to escape
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation
A layer of powdered coke is spread over bauxite (molten electrolyte) during extraction of aluminium. This acts as an insulation and does not allow heat to escape and prevents oxidation. 
Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

In the electrolysis of alumina, cryolite is added to ______________.

  1. lower the melting point of alumina.

  2. increase the electrical conductivity.

  3. minimize the anode effect.

  4. remove the impurities from alumina.
Reveal answer Fill a bubble to check yourself
A,B Correct answer
Explanation

The electrolysis of pure alumina faces some difficulties. Pure alumina is a bad conductor of electricity. The fusion temperature of pure alumina is about 2000$^{\circ}$C and at this temperature when electrolysis is carried out on the fused mass, the metal formed vaporizes, as the boiling point of aluminium is 1800$^{\circ}$C. These difficulties are overcome by using a mixture containing alumina, cryolite $(Na _3,AlF _6)$, and fluorspar $(CaF _2,)$. But the addition of cryolite do not minimize the anode effect and do not remove the impurities from alumina.

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

Which of the following statement(s) is/are correct"?

  1. The chemical processes in the production of steel from haematite ore involve reduction followed by

    oxidation.

  2. In Hall-Heroult process, the electrolyte used is a molten mixture of alumina and cryolite or fluorspar.

  3. Lead is extracted from its chief ore galena by both carbon reduction as well as self reduction,

  4. Haematitic, cassiterite, and argentite are oxide ores.
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

A) In the furnace, first the coke reacts with oxygen in the air blast to produce carbon monoxide(oxidation):$2C+O2\rightarrow 2CO$ The carbon monoxide reduces the iron ore (hematite) to molten iron, becoming carbon dioxide in the process:$3CO + Fe _2O _3\rightarrow 2Fe + 3CO _2$
B) The HallHroult process is the major industrial process for smelting of alumina. It involves dissolving alluminium oxide(allumina) in molten cryolite, and electrolysing the molten salt bath, typically in a purpose-built cell.
C) Lead is extracted from its chief ore galena by both carbon reduction as well as self reduction,
D) Haematitic($Fe _2O _3$),cassiterite ($SnO _2$) and argentite($Ag _2S$).So Haematite and cassiterite are oxide ores but argentite is sulphide ore.Incorrect.
Hence options A,B & C are correct.

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

Aluminium is extracted from alumina $(Al _2O _3)$ by electrolysis of a molten mixture of:

  1. $Al _2O _3 + HF + NaAlF _4$
  2. $Al _2O _3+CaF _2+NaAlF _4$
  3. $Al _2O _3+Na _3AlF _6+CaF _2$
  4. $Al _2O _3+KF+Na _2AlF _6$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
The electrolysis of pure alumina faces some difficulties. Pure alumina is a bad conductor of electricity. 

The fusion temperature of pure alumina is about 2000$^{\circ}$C and at this temperature when electrolysis is carried out on the fused mass, the metal formed vaporizes, as the boiling point of aluminum is 1800$^{\circ}$C. 

These difficulties are overcome by using a mixture containing alumina$(Al _2O _3)$, cryolite $(Na _3AlF _6)$, and fluorspar $(CaF _2)$.

Therefore, the correct option is $C$
Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

In the electrolytic reduction of alumina, the electrolyte is covered with coke powder because, if :

  1. prevents oxidation of aluminium formed

  2. reacts with aluminium forming aluminium carbide

  3. prevents heat loss from electrolyte

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The electrolyte is a molten bath of cryolite and dissolved alumina. Cryolite is a good solvent for alumina with low melting point. The molten electrolyte is maintained at high temperature inside the insulating cell by using high amount of coke powder or dust to prevent the heat loss.

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

Aluminium is extracted by :

  1. Heating sodium aluminium silicate to a high temperature

  2. Treating cryolite with sodium hydroxide solution under pressure

  3. Heating aluminium oxide with coke in a furnace

  4. The electrolysis of molten aluminium oxide in fused cryolite
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Aluminium is extracted by electrolysis. The ore is first converted into pure aluminium oxide by the Bayer Process and this is then electrolysed in solution in molten cryolite another aluminium compound. The aluminium oxide has too high a melting point to electrolyse on its own. The usual aluminium ore is bauxite.

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

The electrolyte used in electrolytic refining of impure aluminium is:

  1. $AlF _3 + CaF _2$
  2. $Na _3AlF _6 + CAF _2$
  3. $AlF _3, Na _3AlF _6$ and $CaF _2$

  4. Any aluminium salt is molten state
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The electrolytes are used to reduce melting point and increase conductivity.

$\therefore $ The electrolytes are $AlF _{6} , Na _{3}AlF _{6} , CaF _{2}$.

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

During electrolysis of aluminium, which of the following substance is used as an electrolyte?

  1. $Al _2O _3$
  2. $Al _2O _3, Na _3AlF _6$
  3. $Al _2O _3, Na _3AlF _6, CaF _2$

  4. None of the above
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The substance which is used as an electrolyte during electrolysis of aluminium is $Al _2O _3, Na _3AlF _6, CaF _2$.

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

Which of the following statements is correct?
(i) Copper is extracted by hydrometallurgy from low-grade ores.
(ii) In the electrolytic reduction of alumina, graphite is acting as an anode and steel vessel with the lining of carbon acts as an anode.
(iii) In Hall-Heroult process, aluminium is obtained at anode and CO and $CO _2$ are produced at the cathode.

  1. (i) only

  2. (i) and (ii) only

  3. (ii) and (iii) only

  4. All of these
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
$(i)$ Copper is extracted by hydrometallurgy from low-grade ores. It is leached out using acid or bacteria. The solution containing $Cu^{2+}$ is treated with scrap iron or $H _2$.
$Cu^{2+} (aq)+H _2 (g)\longrightarrow Cu (s)+2H^+ (aq)$
$(ii)$ In the electrolytic reduction of alumina. The graphite act as anode and steel with a lining of carbon acts as an anode.
$(iii)$ The process of extracting Aluminium from Alumina $(Al _2O _3)$ by electrolysis is called Hall-Heroult process. In this process Aluminium is produced at cathode which is obtained by outlet, oxygen is released at an anode. It reacts with carbon of anode producing $CO$ and $CO _2$.
Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

Cryolite and fluorspar are mixed with $Al _2O _3$ during electrolysis for extraction of aluminium to:

  1. increase the mass of the reaction mixture

  2. get other products at anode like fluorine

  3. lower the melting point and increase the conductivity of the electrolyte

  4. reduce aluminium oxide by cryolite
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In the metallurgy of Aluminium, purified $Al _2O _3$ is mixed with $Na _3AlF _6$ or $CaF _2$ which lowers the melting point of mix and brings conductivity.

Multiple choice chemistry production of metals extraction of aluminium metallurgy of aluminium extraction of metals by electrolysis

In the metallurgy of aluminium:

  1. $Al^{3+} $ is oxdised to $Al _{(s)}$

  2. graphite anode is oxidised to carbon monoxide and carbon dioxide

  3. oxidation state of oxygen changes in the reaction at anode

  4. oxidation state of oxygen changes in the overall reaction involved in the process
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
The oxidation state of $'O'$ does not change i neither the reaction occurring at the anode or the overall reaction as shown below.
At anode:-$C+{ O }^{ 2- }\longrightarrow CO+2{ e }^{ - };C+2{ O }^{ 2- }\longrightarrow C{ O } _{ 2 }+4{ e }^{ - }$
The released electrons used at cathode and here Graphite  is oxidized to $'CO'$ and $C{ O } _{ 2 }$