MHT CET · Chemistry · General Principles and Processes of Isolation of Metals

In leaching of alumina from bauxite by Bayer’s process, then ore is treated with

A $N a O H (a q)$
B $N a C N (a q)$
C $K C N (a q)$
D $N a_{2} C O_{3} (a q)$

Verified Solution

Answer & Solution

Correct Answer

(A) $N a O H (a q)$

Step-by-step Solution

Detailed explanation

In leaching of alumina from bauxite by Bayer’s process, the ore is treated with NaOH (aq). Concentration is carried out by heating the powdered ore with a concentrated solution of NaOH at
$473-523 K$ and $35-36$ bar pressure. $Al _2 O _3$ is extracted out as sodium aluminate.
$Al _2 O _3(s)+2 NaOH (a q)+3 H _2 o(l) \rightarrow$ $2 Na \left[ Al ( OH )_4\right](a q)$
The sodium aluminate formed is neutralised by passing $C O_2$ gas and hydrated $A l_2 O_3$ is precipitated.
$2 Na \left[ Al ( OH )_4\right]( aq )+ CO _2(g) \rightarrow Al _2 O _3$ $. x H _2 O ( s )+2 NaHCO _3( aq )$

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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