Question

Highest specific surface is observed in

• A. Kaolinite
• B. Montmorillonite
• C. Illite
• D. Chlorite

Hint:

Specific Surface Ranking: Montmorillonite ($700-800\text{ m}^2\text{/g}$) $>$ Vermiculite ($600-800$) $\gg$ Illite ($100$) $>$ Kaolinite ($10-30\text{ m}^2\text{/g}$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Specific surface area ($m^2/g$) is the total external and internal surface area per unit mass of a clay mineral, determining its adsorption and swelling properties.
Key Formula or Approach:
\[ \text{Specific Surface: } \text{Montmorillonite (700--800 } \text{m}^2\text{/g)} \gg \text{Illite (80--120)} > \text{Kaolinite (10--30)} \]

Step 2: Detailed Explanation:
Comparing specific surface areas of primary phyllosilicate clay minerals:
1. Montmorillonite (Smectite group): An expanding 2:1 clay mineral with flexible interlayer bonding. Water and ions penetrate between crystal sheets, providing extensive internal and external surface area: 700 to 800 $\text{m^2\text{/g}$}.
2. Illite: Non-expanding 2:1 clay fixed by potassium ($K^+$) ions: \(80 - 120\text{ m}^2\text{/g}\).
3. Kaolinite: Rigid non-expanding 1:1 clay bound by strong hydrogen bonds with external surface only: \(10 - 30\text{ m}^2\text{/g}\).
4. Chlorite: 2:1:1 non-expanding clay: \(70 - 150\text{ m}^2\text{/g}\).

Step 3: Final Answer:
Hence, highest specific surface is observed in Montmorillonite, matching option (B).