Hardness is defined as the soap consuming capacity of a water sample. Generally, soaps consist of the sodium salts of long fatty acids (such as oleic acid, palmic acid and stearic acid). The soap consuming capacity of a water largely due to the presence of Ca+2and Mg+2ions as they form insoluble scums of calcium and magnesium soaps which do not have any detergent value.

For softening of water by zeolite process, hard water is percolated at a specified rate through a bed of zeolite. Zeolite holds sodium ion loosely and can be represented as Na2Z, where Z represents insoluble radical frame work.

When the water passes through the zeolite the hardness causing ions (Ca+2, Mg+2etc.) are retained by the zeolite as CaZ and MgZ respectively, while the outgoing water contains equivalent amount of sodium salts. The block diagram and chemical reactions taking place in zeolite softener are:

After some time, when the zeolite is completely changed into calcium and magnesium zeolites, then it gets exhausted (saturated with Ca+2and Mg+2ions) and it ceases to soften water. It can be regenerated and reused by treating it with a 10% brine (sodium chloride) solution.

CaZ + 2NaCl® Na2Z+ CaCl2

MgZ + 2NaCl® Na2Z+ MgCl2