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Water hardness is caused by the presence of dissolved salts of calcium and magnesium. There are two types of hardness: temporary and permanent. Temporary hardness is due to bicarbonates of calcium and magnesium and can be removed by boiling or by adding lime. Permanent hardness, however, is caused by the sulphates and chlorides of calcium and magnesium, and it cannot be removed by simple boiling.
To remove permanent hardness, special methods are used. One of the most effective methods is the zeolite process, also called the permutit process. Zeolites are hydrated sodium aluminosilicates that can exchange their sodium ions with calcium and magnesium ions present in hard water. When hard water passes through a bed of zeolite, calcium and magnesium ions are replaced by sodium ions, which do not cause hardness. The water coming out of the zeolite bed is soft and free from permanent hardness.
The exhausted zeolite can be regenerated by washing with a concentrated solution of sodium chloride (common salt). This process restores the sodium ions in the zeolite, making it ready for reuse. Thus, zeolite treatment is not only effective but also economical for large-scale water softening.
Looking at the options:
Sulphonides are not used for water treatment.
Lime is effective only for temporary hardness, not for sulphates.
Nitrates are unrelated to hardness removal.
Therefore, the correct answer is zeolites, which specifically remove permanent hardness caused by sulphates and chlorides of calcium and magnesium. This method is widely used in households, industries, and municipal water treatment plants to ensure the supply of soft water for various applications.
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