16
MCQ (Multiple Correct Answer)
In the extraction of aluminium by Hall-Heroult process, purified $\mathrm{Al}_2 \mathrm{O}_3$ is mixed with $\mathrm{CaF}_2$ to
A
lower the melting point of $\mathrm{Al}_2 \mathrm{O}_3$
B
increase the conductivity of molten mixture.
C
reduce $\mathrm{Al}^{3+}$ into $\mathrm{Al}(\mathrm{s})$
D
acts as catalyst
17
MCQ (Multiple Correct Answer)
Which of the following statements is correct about the role of substances added in the froth floatation process?
A
Collectors enhance the non-wettability of the mineral particles.
B
Collectors enhance the wettability of gangue particles.
C
By using depressants in the process two sulphide ores can be separated.
D
Froth stabilisers decrease wettability of gangue.
18
MCQ (Multiple Correct Answer)
In the froth floatation process, zinc sulphide and lead sulphide can be separated by ............ .
A
using collectors
B
adjusting the proportion of oil to water
C
using depressant
D
using froth stabilisers
19
MCQ (Multiple Correct Answer)
Common impurities present in bauxite are ............. .
A
CuO
B
ZnO
C
$\mathrm{Fe}_2 \mathrm{O}_3$
D
$\mathrm{SiO}_2$
20
MCQ (Multiple Correct Answer)
Which of the following ores are concentrated by froth floatation?
A
Haematite
B
Galena
C
Copper pyrites
D
Magnetite