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Cyanide or Macarthur Forrest Process

Which of the ...

Question

Which of the following reduction reactions are actually employed in commerical extraction of metals?

F e_{2} O_{3}

2 A l

\to

A l_{2} O_{3}

2 F e

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C r_{2} O_{3}

2 A l

\to

A l_{2} O_{3}

2 C r

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2 N a [A u (C N)_{2}]

Z n

\to

N a_{2} [Z n (C N)_{4}]

2 A u

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C u_{2} S

P b

\to

C u

P b S ↓

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Solution

The correct options are
B $C r_{2} O_{3}$ + $2 A l$ $\to$ $A l_{2} O_{3}$ + $2 C r$
C $2 N a [A u (C N)_{2}]$ + $Z n$ $\to$ $N a_{2} [Z n (C N)_{4}]$ + $2 A u$
(A) Iron is commercially extracted by reduction with C and CO.
$F e_{2} O_{3} + 3 C O \to 2 F e + 3 C O_{2}$
$F e_{2} O_{3} + 3 C \to 2 F e + 3 C O$
Thus option A is incorrect.

(B) Chromium is extracted commercially by reduction with aluminum
$C r_{2} O_{3} + 2 A l \to 2 C r + A l_{2} O_{3}$
Thus option B is correct.

(C) Leaching of $A u_{2} S$ is carried out by heating it with a dilute solution of NaCN in presence of $O_{2}$ .
$A u_{2} S + 4 N a C N ⇌ 4 N a^{+} 2 [A u (C N)_{2}]^{2 -} + S^{2 -}$
Treatment of the cyanide compound with zinc gives displacement reaction in which gold is obtained.
$2 N a [A u (C N)_{2}] + Z n \to [Z n (C N)_{4}]^{2 -} + 2 A u ↓ .$
Thus option C is correct.

(D) The commercial metallurgical process for the formation of metallic copper from the sulphide ore involves oxidation of $C u_{2} S$ to $C u_{2} O$ and auto reduction of a mixture of $C u_{2} S$ and $C u_{2} O$ to copper metal.
$C u_{2} S + \frac{3}{2} O_{2} \to C u_{2} O + S O_{2}$
$2 C u_{2} O + C u_{2} S \to 6 C u + S O_{2}$
Thus option D is incorrect.

Hence, options B and C are correct.

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