Temporary hardness can also be removed by using slaked lime; Ca(OH)2.
This method of removing hardness on a large scale is known as Clark’s method. This is a chemical method. In this method, temporarily hard water containing hydrogen carbonates of Ca and Mg is treated with slaked lime in the tanks. The hydrogen carbonates of Ca and Mg are converted into their insoluble carbonates. These insoluble carbonates settle down at the bottom of tanks, while soft water is drained off for the use.
(ii) By using Zeolite Permutit:
Permutit is an ion-exchange resin used industrially and in the home for softening water. It is a naturally occurring sodium aluminium silicate, commonly called sodium zeolite which can also be prepared artificially. As hard water is passed through the resin, the sodium ions will go into the solution while the unwanted Ca and Mg ions take their place in the complex insoluble Ca and Mg zeolites and their hardness are removed. Soft water is then drawn out at the bottom.
Sodium zeolite can be regenerated by passing a strong NaCl solution through Ca – zeolite.