In the metallurgy of Zn the Zn dust obtained from roasting and reduction of zinc sulphide contains some ZnO. It is removed by

Options

A. absorbance of ultraviolet light and reemission of white light.
B. shock cooling by contact with a shower of molten lead.
C. X-ray method.
D. smelting

Explanation

To solve the problem of removing ZnO from the zinc dust obtained during the metallurgy of zinc, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Context**:
- Zinc is extracted from zinc sulfide (ZnS) through a process that involves roasting and reduction. During this process, some zinc oxide (ZnO) is also formed alongside the desired zinc metal.

2. **Identifying the Problem**:
- The zinc dust obtained contains both zinc metal and zinc oxide. The goal is to remove the unwanted ZnO to obtain pure zinc.

3. **Exploring Methods for Removal**:
- The methods mentioned for removing ZnO include:
- Absorbance of ultraviolet light and re-emission of white light
- Shock cooling by contact with a shower of molten lead
- X-ray method
- Smelting

4. **Analyzing Each Method**:
- **Absorbance of Ultraviolet Light**: This method is not practical for separating solid ZnO from zinc dust.
- **Shock Cooling with Molten Lead**: This method does not specifically target ZnO removal and is not a standard practice in metallurgy.
- **X-ray Method**: While X-ray techniques can analyze materials, they are not typically used for physical separation in metallurgy.
- **Smelting**: This is a traditional method used in metallurgy to extract metals from their ores. In the case of zinc, smelting involves heating the zinc concentrate to a high temperature to convert it into pure zinc while allowing the ZnO to be removed as a byproduct.

5. **Conclusion**:
- The most effective method for removing ZnO from the zinc dust is **smelting**. This process allows for the extraction of pure zinc while effectively dealing with the presence of ZnO.

### Final Answer:
The ZnO in the zinc dust obtained from roasting and reduction of zinc sulfide is removed by **smelting**.

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