Consider the following statements :
Statement I :Activated carbon is a good and an attractive tool to remove pollutants from effluent streams and to remediate contaminants from various industries.
Statement II :Activated carbon exhibits a large surface area and a strong potential for adsorbing heavy metals.
Statement III :Activated carbon can be easily synthesized from environmental wastes with high carbon content.
Which one of the following is correct in respect of the above statements?
(a) Both Statement II and Statement III are correct and both of them explain Statement I
(b) Both Statement II and Statement III are correct but only one of them explains Statement I
(c) Only one of the Statements II and III is correct and that explains Statement I
(d) Neither Statement II nor Statement III is correct
The correct answer is (a) Both Statement II and Statement III are correct and both of them explain Statement I.
Explanation
- Statement I: Correct. This statement is true. Activated carbon is one of the most widely used and effective materials for filtration and remediation. It is used in everything from home water filters to large-scale industrial systems to remove pollutants.
- Statement II: Correct. This is the scientific explanation for how activated carbon works. The “activation” process creates a vast network of microscopic pores, giving it an incredibly high surface area. This large surface area provides countless binding sites for pollutant molecules (like heavy metals, organic chemicals, and dyes) to stick to, a process called adsorption.
- Statement III: Correct. This is the economic and sustainability explanation for why activated carbon is such a popular choice. It is not a rare or expensive material. It can be manufactured from a wide variety of cheap, readily available, carbon-rich “waste” materials, such as coconut shells, wood chips, and nutshells.
Evaluating the Relationship
- Statement I says activated carbon is a “good and an attractive” tool.
- Statement II explains why it is “good” (i.e., effective): its large surface area allows it to adsorb pollutants.
- Statement III explains why it is “attractive” (i.e., appealing to use): it can be easily and cheaply made from environmental waste products.
Since both statements II and III are correct, and both provide key reasons for the assertion in Statement I, option (a) is the correct choice.
Learn More
Key Concept: Adsorption vs. Absorption
It is crucial to understand that activated carbon works by adsorption, not absorption.
- Absorption is a bulk phenomenon where a substance diffuses into a liquid or solid to form a solution. (e.g., a sponge absorbing water).
- Adsorption is a surface phenomenon where particles stick to the surface of another substance. (e.g., pollutants adhering to the porous surface of activated carbon).
How is Activated Carbon Made?
The process generally involves two stages, which is why it’s so “attractive” (Statement III) as a use for waste:
Activation: This char is then “activated” to create its porous structure. This is done by exposing it to an oxidizing agent (like steam or carbon dioxide) at even higher temperatures. This etches away parts of the internal carbon structure, creating a massive network of tiny pores and drastically increasing the surface area.
Carbonization (Pyrolysis): A carbon-rich raw material (like coconut shells or wood) is heated at high temperatures in an environment without oxygen. This burns off all the non-carbon elements and leaves a carbon “char.”
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