From the following, the correct statements about the role of substances added in the froth flotation process are:

a. Collectors enhance the non-wettability of the mineral particles.
b. Collectors enhance the wettability of gangue particles.
c. By using depressants in the process, two sulphide ores can be separated.
d. Froth stabilisers decrease the wettability of gangue.


1. a and b
2. b and c
3. c and d
4. a and c


 



HINT: Sulphide ores can be separated by depressants.
Explanation:
The Froth floatation process is used to extract metal from sulphide ore. This method utilises collectors and depressants whose functions are as follows: 
(i) Collectors enhance the non-wettability of the mineral particles. Hence, the first statement is the correct statement.
(ii) By using depressants in the process of froth floatation two sulphide ores can be separated. e.g., sodium cyanide is used as a depressant to separate lead sulphide ore from zinc sulphide ore.

Hence, the first and third are the correct statements. 

Collectors enhance the wettability of gangue particles. It is the wrong statement

Froth stabilizer has nothing to do with wettability. Froth stabilisers (e.g., cresols, aniline) stabilise the froth. 

Hence statement fourth is incorrect. 

Thus, option fourth is the correct answer.