Question

Sometimes it is possible to separate two sulphide ores by adjusting the proportion of oil to water or by using depressants. When a depressant NaCN is added to an ore containing ZnS and PbS, what is the correct observation?

• A. NaCN prevents PbS from coming to the froth but allows ZnS to come with froth.
• B. NaCN prevents ZnS from coming to the froth but allows PbS to come with froth
• C. NaCN prevents frothing of both ZnS and PbS, hence no froth is formed.
• D. NaCN does not act as depressant hence a mixture of PbS and ZnS is found in froth.

Answer 1

Answer: (B)

NaCN prevents ZnS from coming to the froth but allows PbS to come with froth

Answer 2

NaCN acts as a depressant it selectively prevents ZnS from coming to froth by forming a complex $Na_{2}\lbrack Zn(CN)_{4}\rbrack$ but allows PbS to come with froth.