Zeolite Process

Zeolite Process,Types of Zeolite,Process,Reactions,Regeneration,Limitations of process,Advantages of process,Disadvantages of process

1. Zeolite Process

2. What is Zeolite? Zeolite is hydrated sodium alumino silicate. Zeolites are also known as permutits . Zeolite is capable of exchanging reversibly its sodium ions for hardness- prodcing ions in water. Chemical Structure : Na 2 O.Al 2 O 3 .xSiO 2 .yH 2 O,where X=2-10 and Y=2-6.

3. Types of Zeolite Zeolites are of two types: Natural zeolite : Natural zeolite are non-porous. for example,natrolite , Na 2 O.Al 2 O 3 .xSiO 2 .yH 2 O. 2. Synthtic zeolite : Synthtic zeolite are porous and posses get structure. They are prepared by heating together china clay,feldspar and soda ash. such zeolites possess higher exchange capacity per unit weight than natural zeolites.

4. Process For softening of water by zeolite process,hard water is percolated at a specified rate through a bed of zeolite, kept in a cylinder. The hardness causing ions(Ca 2+ ,Mg 2+ ,etc.) are retained by the zeolite as CaZe and MgZe ; while the outgoing water contains sodium salts.

5. Reactions Na 2 Ze + Ca (HCO 3 ) 2  CaZe + 2NaHCO 3 Na 2 Ze + Mg(HCO 3 ) 2  MgZe + 2NaHCO 3 (Zeolite) (Hardness) Na 2 Ze + CaCl 2 (or CaSO 4 )  CaZe + 2NaCl (or Na 2 SO 4 ) Na 2 Ze + MgCl 2 (or MgSO 4 )  MgZe + 2NaCl(or Na 2 SO 4 ) (Zeolite) (Hardness)

6. Regeneration After some time, the zeolite is completely is completely converted into calcium and magnesium zeolite and it ceases to soften water, i.e., it gets exhausted. At this stage, the supply of hard water is stopped and the exhausted zeolite is reclaimed by treating the bed with a concentrated (10%) brine ( NaCl ) solution . CaZe (or MgZe ) + 2Nacl  Na 2 Ze + Cacl 2 (or MgCl 2 ) ( Exhausted zeolite ) (Brine) ( Reclaimed (Washings) zeolite) The washing (containing Cacl 2 and MgCl 2 ) are led to drain and the regenerated zeolite bed thus-obtained is used again for softening purpose.

7. Limitations of process: If the supply of water is turbid, the suspended matter must be removed ( by coagulation, filtration, etc.), before the water is admitted to the zeolite bed ; otherwise the turbidity will clog the pores of zeolite bed, thereby making it inactive. If water contains large quantities of coloured ions such as Mn 2+ and Fe 2+ ,they must be removed first, because these ions produce maganese and iron zeolite, which cannot be easily regenerated. Mineral acids, if present in water, destroy the zeolite bed and,therefore , they must be neutralised with soda, before admitting the water to the zeolite softening plant.

8. Advantages of process: It removes the hardness almost completely and water of about 10 ppm hardness is producted . The equipment used is compact, occupying a small space. No impurities are precipitated, so there is no danger of sludge formation in the treatedwater at a later stage. The process automatically adjust itself for variation in hardness of incoming water. It is quite clean. It requires less time for softening. It requires less skill for maintenance as well as operation .

9. Disadvantages of process : The treated-water contains more sodium more sodium salts than in lime-soda process. The method only replaces ca 2+ and Mg 2+ ions, but leaves all the acidic ions ( like HCO 3 - and CO 3 2- ) as such in the softened water . When such softened water (containing NaHCO 3 , Na 2 CO 3 ,etc.) is used in boilers for steam generation, sodium bicarbonate decomposes producing CO 2 , which causes corrosion ;and sodium carbonate hydrolysis to sodium hydroxide, which causes caustic embrittlement . High turbidity water cannot be treated efficiently by this method, because fine impurities get deposited on the zeolite bed, therebyc reating problem for its working .

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