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Sometimes it is possible to separate two...

Sometimes it is possible to separate two sulphide ores by adjusting the proportion of oil to water or by using depressant NaCN is added to an ore conaining 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

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem regarding the separation of zinc sulfide (ZnS) and lead sulfide (PbS) ores using sodium cyanide (NaCN) as a depressant, we can follow these steps: ### Step-by-Step Solution: 1. **Understanding the Froth Flotation Process**: - The froth flotation process is used to separate sulfide ores from gangue (unwanted materials). In this process, a mixture of ore, water, and collectors (like pine oil) is agitated to create froth, which carries the desired mineral to the surface. **Hint**: Recall that collectors increase the non-wettability of the mineral particles, allowing them to attach to air bubbles. 2. **Role of Sodium Cyanide (NaCN)**: - NaCN acts as a depressant in the froth flotation process. A depressant is a substance that selectively prevents certain minerals from floating while allowing others to do so. **Hint**: Remember that depressants are used to enhance the separation of minerals by inhibiting the flotation of specific ores. 3. **Reaction of NaCN with ZnS**: - When NaCN is added to the mixture containing ZnS and PbS, it reacts with ZnS to form a soluble complex, specifically Na2Zn(CN)4 and Na2S. This reaction effectively prevents ZnS from floating. **Hint**: Consider how the formation of a soluble complex affects the behavior of ZnS in the flotation process. 4. **Behavior of PbS**: - Since NaCN does not react with PbS, the PbS will remain unaffected and will float to the surface along with the froth. **Hint**: Think about which minerals are allowed to float and which are not, based on their chemical interactions with the depressant. 5. **Conclusion**: - The correct observation is that NaCN prevents ZnS from coming to froth but allows PbS to come with froth. Therefore, the separation of these two sulfide ores can be effectively achieved using NaCN. ### Final Answer: NaCN prevents ZnS from coming to froth but allows PbS to come with froth.
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