|
|
|
Ion
Exchange
Zeolite - Certain natural materials have the property of exchanging one ion in their structure for another ion in the solution. Typical example is zeolites which are complex sodium alumino-silicates and green sands. Higher exchange rate is possible with synthetic ion exchange materials.
The most common use of ion exchange is for water softening and demineralization of feed water for high pressure boilers which require high purity water. Ion exchange can also be used as an alternative method for treatment of industrial wastewaters such as metal-finishing effluents, by precipitation methods.
|
When used for water softening, sodium ions in the natural zeolite are exchanged for calcium and magnesium ions in the water. Thus complete removal of hardness occurs.
Ca++ or Mg++ + Na2X ca X or Mg X + 2Na+
where Na2X represents a zeolite.
Thus the finished water is high in sodium and this will not create any problem unless the original water is very hard. When all sodium ions in the structure have been exchanged, no further removal of hardness occurs.
|
Zeolite can be regenerated using a salt solution which provides a high concentration of sodium ions to reverse the exchange reaction. In this case hardness is released as a concentrated chloride
Ca X or Mg X +2NaCI →Na2X + CaCl2 or MgCl2
Natural zeolite with sodium cycle will have an exchange capacity of about 200 gm equivalent /m3 and requires 5 equivalents of regenerant / equivalent exchanged. Synthetic sodium cycle resins may have double the exchange capacity.
|
|
|
| |
|
|
|
