Problem 1 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The processes of calcination and roasting in metallurgical industries, respectively, can lead to : (a) Global warming and photochemical smog (b) Global warming and acid rain (c) Photochemical smog and ozone layer depletion (d) Photochemical smog and global warming

Step-by-Step Solution

Answer

The correct answer is (b) Global warming and acid rain.

Step 1: Understanding Calcination

Calcination is a process in which a metal carbonate is heated strongly in the absence of air to convert it into metal oxide and carbon dioxide gas is evolved. The release of CO2 contributes to global warming.

Step 2: Understanding Roasting

Roasting involves heating the ore in the presence of air. This often results in the conversion of sulfide ores into oxides, while releasing sulfur dioxide (SO2). SO2, when released into the atmosphere, contributes to acid rain upon reacting with water vapor.

Step 3: Evaluating the Effects

Based on the processes: calcination generally results in CO2 which is associated with global warming, and roasting yields SO2 which can lead to acid rain. Hence, calcination and roasting contribute to global warming and acid rain, respectively.

Step 4: Selecting the Correct Answer

Comparing the options: (b) Global warming and acid rain corresponds to the effects of calcination and roasting derived in the previous steps.

Key Concepts

Calcination

Calcination is a significant process in the field of metallurgy, crucial for purifying metal ores. It involves heating a metal carbonate in the absence of air to convert it into a metal oxide, a simpler form. Typically, this process is done in rotary kilns or shaft furnaces.

When calcination is carried out, carbon dioxide (CO2) gas is released as a byproduct. This chemical reaction can be represented as follows: \[\text{Metal Carbonate} \rightarrow \text{Metal Oxide} + \text{CO}_2\]

The release of CO2 is not without consequence. One of the major environmental concerns linked with calcination is its contribution to global warming. As CO2 is a well-known greenhouse gas, its accumulation in the atmosphere traps heat, leading to the gradual warming of the planet. Therefore, calcination not only plays a role in metallurgy but also has a significant environmental impact.

Roasting

Roasting in metallurgy involves heating ore in the presence of excess air or oxygen. The primary goal is to oxidize the ore, often converting metal sulfides into oxides while freeing up sulfur dioxide (SO2). This is usually done in a furnace or a specially designed reactor.

The reaction can be summarized as follows:\[\text{Metal Sulfide} + \text{O}_2 \rightarrow \text{Metal Oxide} + \text{SO}_2\]

While roasting is a beneficial process for altering the composition of ore and making it suitable for smelting, it does release SO2.

This gas, when mixed with atmospheric moisture, can lead to acid rain. Acid rain can have harmful effects on soil, water bodies, and vegetation, contributing to environmental degradation and negatively affecting ecosystems. Therefore, roasting, like calcination, has implications for both metallurgy and environmental health.

Environmental Impact in Metallurgy

Metallurgical processes such as calcination and roasting are vital in metal extraction but carry significant environmental impacts. These processes collectively emit gases that can alter atmospheric conditions adversely.

Key concerns include:

• Global Warming: The CO2 emitted during calcination contributes directly to this global issue, as it enhances the greenhouse effect by trapping infrared radiation.
• Acid Rain: SO2, a byproduct of roasting, interacts with water vapor to form sulfuric acid, precipitating as acid rain. This can have severe effects on man-made as well as natural environments.

Mitigating these impacts involves employing modern technologies like gas scrubbing, using alternative, less harmful processes, and promoting research into cleaner metallurgical methods.

It is crucial to balance metallurgical advancements with sustainable practices to protect the environment.