pH shift in softening water

[csaba]

Dear Everyone,

I am wondering about the following phenomenon in water softening applications. Even the ion exchange resin manufacturer could not answer my question so your feedback would be greatly appreciated.

The problem:

If you soften the raw water by removing the Ca++ and the Mg++ ions the water's pH shifts to the acidic direction.

What is its reason and is there some calculable correlation between the hardness degree of water and the pH value?

The resin used is a strongly acidic cation resin (SAC) and
it is regenerated by sodium chloride (NaCl). That is why I have difficulties in finding out the reason and correlation to the shift in the pH. I am not a chemical guy so it is hard for me to conclude.

Is there some kind of correlation like 1 gpg decrease in water hardness equals with ... shift in pH???

Thank you very much in advance!

Csaba

http://www.prominent.com

Experts in chem-feed and water treatment

 

[bimr]

Not quite sure what you are doing since you have posted just a brief description.

However, it is possible to state with absolute certainty that softening of water with ion exchange resin in the sodium cycle will not change or "shift" the pH of the raw water.

 

[DocMax]

Csba

Your question is strange, because in the water softening the pH will not change.
In the water softening you replace the only Ca2+ and Mg2+ with Na+, so the pH not change.
The reactions involved in the process are:

2R-Na + Ca2+ = R2Ca + 2Na+
2R-Na + Mg2+ = R2Mg + 2Na+

Can you give me some more details about your process, what is the chemical analysis of the raw water?

The only way to change the pH in the water is the lowering of alkalinity, but in the softening that not happen.
Did you feed any chemical in the raw water? Please explain better.
Are you sure that you use a SAC resin in the sodium cycle?.
This phenomeenon happen in every cycle of the softener or only at the start up of the plant?
What is the brand of your SAC resin?

Hi
DocMax

 

[GarySCWSVI]

I agree with the comments. Ion Exchange softening has been shown in studies to actually increase pH by 0.2-0.3 points. Not reduce pH.

Gary Schreiber, CWS VI
The Purolite Co.

 

[deposition]

I believe it may have nothing to do with ion exchange chemistry. The softener may be experiencing organic fouling, releasing acids either from bacteria or organic chemicals. You can verify the guess by sampling a column of resin for microscopic examination and a caustic rinse wash.

 

[csaba]

Dear All,

Thanks a lot for your help!

Meanwhile I also carried out some research: there should be really some kind of specific application problem still unknown for us that reduces the pH and it is - as you say - not the water softening process.

http://www.prominent.com

Experts in chem-feed and water treatment