Collectors like pine oil, xanthenes etc…enhance the non-wettability of sulphide ore because mineral particles become wet by oils while gangue particles are wet by water. So, separation becomes easier.

If there are two sulphides ores present and we want to separate one of them, then depressants are used. Depressants like NaCN selectively allow one sulphide ore to come to the froth.

If the ore contains ZnS and PbS, then the depressant NaCN will let PbS to come to the froth and ZnS will not form the froth.