Question

Sometimes it is possible to separate two sulphide ores by adjusting the proportion of oil to water 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 the froth

Answer 1

The correct option is B $NaCN$ prevents $ZnS$ from coming to the froth but allows $PbS$ to come with froth

• Froth floatation method is used for removing gangue from sulphide ores. In this process, a suspension of the powdered ore is made with water.
• It is possible to separate two sulphide ores by adjusting the proportion of oil to water or by using ‘depressants’.
• In the case of an ore containing $ZnS$ and $PbS$, the depressant used is $NaCN$. It selectively prevents $ZnS$ from coming to the froth but allows $PbS$ to come with the froth.