i) Principle ii) Softening and regeneration reactions iii) Process iv) Advantages

FE > Semester 1 > Applied Chemistry 1

Marks : 06

Years : DEC 2015

Principle- Zeolite is micro-porous mineral which is used as catalyst in many industrial purposes such as water purification and air purification.

ii) Softening and regeneration reactions- 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 $(Ca^{+2}, Mg^{+2}$ etc.) 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 $Ca^{+2}$ and $Mg^{+2}$ ions) and it ceases to soften water. It can be regenerated and reused by treating it with a 10% brine (sodium chloride) solution. Regeneration reactions are

$CaZ + 2NaCl \rightarrow Na_2Z + CaCl \\ MgZ + 2NaCl \rightarrow Na_2Z + MgCl_2$

Advantages- It removes the hardness almost completely (about 10 ppm hardness only). The process automatically adjust itself for variation in hardness of incoming water. This process does not involve any type of precipitation, thus, no problem of sludge formation occurs.