MetallurgyMedium
Question
Match column I with column II and select the correct answer using the codes given below the lists :
Column I Column II
I. Cyanide process. (a) Ultra pure Ge
II. Froth floatation process. (b) Pine oil.
III. Electrolytic reduction. (c) Extraction of Al.
IV. Zone refining. (d) Extraction of Au.
Column I Column II
I. Cyanide process. (a) Ultra pure Ge
II. Froth floatation process. (b) Pine oil.
III. Electrolytic reduction. (c) Extraction of Al.
IV. Zone refining. (d) Extraction of Au.
Options
A.I - (c), II - (a), III - (d), IV - (b)
B.I-(d), II-(b), III-(c), IV-(a)
C.I-(c), II-(b), III-(d), IV-(a)
D.I-(d), II-(a), III-(c), IV-(b)
Solution
(I) 4Au / Ag (s) + 8CN-(aq) + 2H2O(aq) + O2(g) → 4[Au / Ag (CN)2]-(aq) + 4OH-(aq)
2[Au / Ag (CN)2]-(aq) + Zn(s) → 2Au / Ag (s) + [Zn(CN)4]2- (aq)
(II) This method is based on the fact that gangue and ore particles have different degree of wettability with water and pine oil; the gangue particles are preferentially wetted by water while the ore particles are wetted by oil.
(III) Electrolytic reduction (Hall-Heroult process) :
The purified Al2O3 is mixed with Na3AlF6 (cryolite) or CaF2 (fluorspar) ) which lowers the melting point of the mixture and increases conductivity. The fused matrix is electrolysed. The electrolytic reactions are :
Cathode : Al3+ (melt) + 3e- Al(l)
Anode : C(s) + O2- (melt) CO(g) + 2e-
C(s) + 2O2- (melt) CO2 (g) + 4e-
(IV) This process is used when metals are required in very high purity, for specific application. For example pure Si and Ge are used in semiconductors and hence are purified by this method. Zone refining method is based on the principle that an impure molten metal on gradual cooling will deposit crystals of the pure metal, while the impurities will be left in the remaining part of the molten metal.
2[Au / Ag (CN)2]-(aq) + Zn(s) → 2Au / Ag (s) + [Zn(CN)4]2- (aq)
(II) This method is based on the fact that gangue and ore particles have different degree of wettability with water and pine oil; the gangue particles are preferentially wetted by water while the ore particles are wetted by oil.
(III) Electrolytic reduction (Hall-Heroult process) :
The purified Al2O3 is mixed with Na3AlF6 (cryolite) or CaF2 (fluorspar) ) which lowers the melting point of the mixture and increases conductivity. The fused matrix is electrolysed. The electrolytic reactions are :
Cathode : Al3+ (melt) + 3e- Al(l)
Anode : C(s) + O2- (melt) CO(g) + 2e-
C(s) + 2O2- (melt) CO2 (g) + 4e-
(IV) This process is used when metals are required in very high purity, for specific application. For example pure Si and Ge are used in semiconductors and hence are purified by this method. Zone refining method is based on the principle that an impure molten metal on gradual cooling will deposit crystals of the pure metal, while the impurities will be left in the remaining part of the molten metal.
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