You are given a mixture of `ZnS and PbS`. The two compounds can be separated by

Options

A. froth flotation on adding `NaCN`
B. electromagnetic separation
C. handpicking
D. leaching with `NaCN`

Answer

To separate a mixture of ZnS (zinc sulfide) and PbS (lead sulfide), we can use the froth flotation method. Here’s a step-by-step explanation of the process:

### Step 1: Understanding Froth Flotation
Froth flotation is a process used to separate hydrophobic materials from hydrophilic ones. In this case, we want to separate ZnS from PbS.

**Hint:** Froth flotation relies on the differences in the surface properties of the minerals.

### Step 2: Adding a Depressant
In the froth flotation process, we can add a depressant to selectively inhibit one of the minerals. For separating ZnS from PbS, sodium cyanide (NaCN) is commonly used as a depressant.

**Hint:** A depressant is a substance that prevents a specific mineral from floating.

### Step 3: Reaction with Sodium Cyanide
When NaCN is added to the mixture, it reacts with ZnS to form sodium zinc cyanide (Na2Zn(CN)4). This reaction makes ZnS hydrophilic, preventing it from forming froth.

**Hint:** The formation of a complex with the depressant alters the surface properties of the mineral.

### Step 4: Froth Formation
As air is bubbled through the mixture, the PbS particles, which are not affected by NaCN, will become hydrophobic and will attach to the air bubbles, rising to the surface to form a froth.

**Hint:** Only the mineral that is not inhibited by the depressant will float.

### Step 5: Collecting the Froth
The froth that forms on the surface contains the PbS, which can be collected, while the ZnS remains in the slurry.

**Hint:** The collection of froth is the final step in obtaining the desired mineral.

### Final Answer
The two compounds ZnS and PbS can be effectively separated by the froth flotation method using sodium cyanide as a depressant.

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