2 replies to this topic

[tractable09]

Dears,
I am new to water treatment side and I am given a task to evaluate existing ion exchange resin performance. In a simple flow scheme, Water at 230 T/hr is passed through a cation exchanger ----->Anion Exchanger.......>Mix bed polisher.......>polish water tank.
I have started with Cation exchanger and I have lab results with me.
Lab Result of Cation Exchanger:
Inlet:
Ca = 34 ppb
Na = 16 ppb
Ammonia = 2221 ppb
Sulphate = 2121 ppb
Total Cations = 125 meq/L
Total Anions = 144 meq/L
Ph = 7.26
I get confused here as If I sum Cations (Na, Ca, NH4) they do not bcomes equal to 125 meq/L, neither Anion Sulphate of 2121 ppb is equal to total Anions 144 meq/L

Outlet results:
Ca = 340 ppb
Na = ND
Ammonia = ND
Sulphate = 62.42 ppb
pH=3.53
Now comes the 2nd confusion, how Ca can increase after passing water through Cation exchanger?
and Why SO4 came down at out let?
How the pH came down at outlet?
Really appreciated if anyone experience can throw light, thanks in advance.
Regards,

[markymaark]

Is there Alkalinity present? That could be the answer to cation/anions not adding up.

Also, meq/L= ppm*V/MW. Where V is valence and MW is molecular weight. So your meq/L values are incorrect.

Secondly, the results seem very odd. Judging by the outlet it would appear the cation exchanger is actually either a WAC or SAC. Normally sodium exchanges for Ca or Mg. But it all depends on the resin and it's affinity for larger, higher valence ions.

I would assume a WAC/SAC due to the large pH drop (from H+ exchange).

There are many confusions that could be cleared up by attaching the Techincal Data Sheet for your specific resin:
1) pH drop
2) Ca rise
3) Sodium depletion with NH4+ depletion
4) Sulfate (anion) drop across a cation exchanger

From the many contradictions I would have to assume that the low ppb values are giving faulty measurements or your spectroscopy is off.

No Cation Exchanger would drop pH, increase Ca, lower Na/NH4 and lower anion concentration.

[bmk]

The cation load for inlet water is calculated as under:-
Ca ++ = 34/20=1.7 eq.pb or meq./mL
Na+ =16/23=0.696
NH4+=2221/18=123.389
Total cation =125.78 meq./L

Anion SO4 -2 =2121/48 = 44.18

If you use cation exchanger resin in the form of H+ ions you will naturally get outlet water with acidic pH and same anion as sulphate.
There is some mistake in reporting presence of Ca +2 in outlet water from cation resin column.--- bmkhare

Edited by bmk, 05 December 2012 - 10:18 PM.