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In my textbook, NCERT Chemistry for class 12, it is mentioned that one of the principle of froth floatation method is the following:

The mineral particles become wet by oils while the gangue particles by water. Source

Definition of wetting:

Wetting is the ability of a liquid to maintain contact with a solid surface, resulting from intermolecular interactions when the two are brought together. Source

My question is, why is it that minerals are wet exclusively by oils and gangue particle by water only?

An idea that I came up with is that gangue particles may be generally hydrophobic and hence repelled into the layer with collector, but is there any reason to why the particles must be hydrophobic? In another way, given an ore, it consists of gaunge and the actual mineral of interest, now why must it be the gaunge part is always hydrophobic?

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    $\begingroup$ For further reading, Froth flotation ( flotation process) $\endgroup$
    – Poutnik
    Commented Aug 6, 2021 at 14:01
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    $\begingroup$ Because of the additives put into the solutions. $\endgroup$ Commented Aug 6, 2021 at 14:31
  • $\begingroup$ I understand that part: The additives are the collectors and froth stabiliser according to my book, now I understand that collector is some oily substance and for the water part, that is the original solution. $\endgroup$
    – Babu
    Commented Aug 6, 2021 at 14:35

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The gangue is mainly made of clay, and clay is a mixture of aluminosilicates which are hydrophilic, because their structure is surrounded by $\ce{-O-H}$ bonds. $\ce{O-H}$ bonds can make hydrogen bond with water, so they are easily wet by waters. If minerals are crystallized and not surrounded by these same bonds, they are hydrophobic. It is the case for pyrite $\ce{FeS2}$ or blende $\ce{ZnS}$, etc. They are more easily wet by oils than by water..

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