Question

The following methods are not advisable to extract zinc from its oxide ore. (a) Reduction with aluminium (b) Reduction with \(\mathrm{H}_{2}\) (c) Electrolytic reduction (d) Reduction with carbon

Short answer

Reduction with hydrogen is not advisable for zinc oxide extraction.

Step-by-step solution

Understanding Zinc Metallurgy

Zinc is commonly extracted from its oxide ore, zinc oxide (ZnO), by reduction. When selecting a reduction method, it's important to consider the reactivity of zinc, which is a moderately reactive metal.

Analyzing Reduction with Aluminium (Thermite Process)

The thermite process involves using a more reactive metal, like aluminium, to reduce a metal oxide. However, this method is typically used for extracting metals such as chromium and not for zinc extraction, as it is economically inefficient for zinc.

Examining Reduction with Hydrogen

Hydrogen can be used to reduce metal oxides, but it is not suitable for zinc oxide reduction. Zinc has a higher affinity for oxygen than hydrogen, making this method inefficient and inappropriate for zinc extraction.

Considering Electrolytic Reduction

Electrolytic reduction involves using electricity to reduce metal ions to their elemental form. While this method is applicable to metals like aluminium, zinc is not typically extracted this way because it's less economical when compared to other methods such as the electrolysis of zinc sulfate solution.

Reviewing Reduction with Carbon

Reduction with carbon (coke) is suitable for metal oxides of less reactive metals. Zinc oxide can be reduced with carbon via the following reaction: \( \text{ZnO} + \text{C} \rightarrow \text{Zn} + \text{CO} \). However, this method is not advisable due to the high temperatures required and the risk of producing impurities.

Conclusion

Among all these methods, the least advisable for zinc oxide is reduction with hydrogen, due to its ineffectiveness in reducing zinc oxide based on reactivity series.

Key concepts

Reduction with Aluminium

Reduction with aluminium, known as the thermite process, is not a viable method for extracting zinc from its oxide ore. This method involves using a highly reactive metal such as aluminium to displace a less reactive metal from its oxide. However, for zinc, this process is economically inefficient. The thermite process is more suited for extracting metals like chromium due to the high energy and cost demands involved. Therefore, the use of aluminium in zinc extraction is generally avoided due to these economic considerations.

Electrolytic Reduction

Electrolytic reduction is a process that utilizes electrical energy to convert metal ions in a solution into pure metal. While this method is effective for metals like aluminium, zinc extraction through electrolytic reduction is rarely applied. This is primarily because it is less cost-effective compared to methods using zinc sulfate solutions. The electricity consumption required for this process adds to the expense, making other techniques more favorable when extracting zinc from its ore.

Reduction with Carbon

The reduction with carbon, often using coke, involves the chemical reaction between zinc oxide and carbon to produce zinc and carbon monoxide: \[ \text{ZnO} + \text{C} \rightarrow \text{Zn} + \text{CO} \].
This method, suitable for less reactive metals, falls short for zinc extraction. One reason is the high temperature needed for the reduction, which can introduce impurities into the zinc, compromising its quality. Moreover, the economic implications of maintaining such temperatures make this method less practical. As a result, reduction with carbon is not the preferred choice for zinc metallurgy.

Zinc Metallurgy

Zinc metallurgy primarily involves the extraction and processing of zinc from its ores. Zinc oxide, one of the most common forms, is typically reduced using different methods based on cost-efficiency and practicality. The choice depends on zinc's position in the reactivity series as a moderately reactive metal. Ultimately, the key focus in zinc metallurgy is choosing a method that balances energy efficiency, cost, and quality of the produced zinc.

Reduction with Hydrogen

Reduction with hydrogen involves using hydrogen gas to react with metal oxides, freeing the metal. However, this method is unsuitable for zinc oxide due to zinc’s higher affinity for oxygen than hydrogen. This makes the process inefficient and ineffective. Even though it might be environmentally preferable due to fewer pollutants like carbon dioxide, the inefficiency in reducing zinc oxide makes it an impractical choice in zinc extraction methods.