Calcium Carbonate to Neutralize Low pH

TheEngineer · Mar 21, 2016

I added an acid neutralizer to my house last week. The neutralizer uses calcite. I was trying to figure out if the calcite will help me with the CO2 problem I have with my RODI system. I currently have to aerate my RO water for 24 hours before passing it through the DI resin because of high CO2. The process works, but it is a pain in the butt.

Now that I have the acid neutralizer, is my CO2 problem improved or gone? Chemistry is not my thing, but I can google with the best of them

Here's what I think happens in my neutralizer:

Calcium carbonate + hydrogen ions = Calcium + CO2 + Water
Calcium carbonate + CO2 + water = calcium bicarbonate

Does this mean that the CO2 should be absorbed into the calcium bicarbonate making it something my RO membrane can reject? If so, would it be enough to stop excess CO2 from passing into my DI?

Randy Holmes-Farley · Mar 21, 2016

It will convert some of the CO2 (H2CO3) into Ca++ and HCO3-, which will be rejected better by the RO membrane.

So using the process on the pre-RO water may help extend the life of the DI resin. How much depends on how high the pH is being driven by the calcite.

TheEngineer · Mar 21, 2016

Thanks. I only have a little left of the current batch of DI resin. I might just blow through the last of it to test if I still need to aerate.

Randy Holmes-Farley · Mar 22, 2016

Let us know what happens.

TheEngineer · Mar 22, 2016

Will do.

TheEngineer · Mar 24, 2016

I haven't redone the plumbing to go straight from the RO into the DI yet, but that's on my list for the weekend.

I did make some new water yesterday and noticed, as expected, my TDS a little more than doubled from 65-75 to around 165. I wasn't sure how my output TDS would change from the RO, I assumed it would go up. To my surprise, my efficiency went from around 98% to 99.3% and the output TDS stayed at 1. I was typically either 2-3. Perhaps the acid neutralizer is making the dissolved solids easier to pull out?

Randy Holmes-Farley · Mar 24, 2016

icecool2 said:
Perhaps the acid neutralizer is making the dissolved solids easier to pull out?

Yes, that would be the reason to use it. Calcium (96-98%) and bicarbonate (95-96%) are much better rejected by the RO membrane than CO2 which is rejected very poorly (data are for a TFC membrane). The same effect can be accomplished by adding sodium hydroxide to the water.

TheEngineer · Mar 24, 2016

Does CO2 affect TDS readings?

Randy Holmes-Farley · Mar 24, 2016

Somewhat, but not as much as it depletes a DI. The only way it impacts TDS is as some of it dissociates into H+ and HCO3-.

TheEngineer · Mar 25, 2016

I got around to switching my plumbing to see where my DI consumption would be. Not good. It's not as bad as it used to be, but after making 5 gallons of RODI, there was a noticeable color change in the DI. Oh well! Buckets and airstones are still in my future.

mb167204 · Apr 3, 2019

TheEngineer said:
I got around to switching my plumbing to see where my DI consumption would be. Not good. It's not as bad as it used to be, but after making 5 gallons of RODI, there was a noticeable color change in the DI. Oh well! Buckets and airstones are still in my future.

Hey Do you mind telling me which pump you used to get your water through the DI resin canister.