DI question

[Rick O]

I need to replace my DI resin. Can someone tell me the difference in cation and anion? I have separate refillable cartridges for each.

[Rick O]

Tom? Jerel?

[Spanky]

Don't ask me. Don't some of those come mixed already?

This is something you need a water expert for.

[Rick O]

I thought this was a chemistry question. Aren't you and Tom the experts in that field?

[DKKA]

I believe the simple/conventional answer is that one removes positively charged ions, the other removes negatively charges ions. If that holds water, then you need them both.

You might try www.resindepot.com for a source for bulk resins.

hth,
Dan

[clowningaround]

You could talk to these guys they really know the water business. they always seem to be there any time of day. www.airwaterice.com

[Rick O]

Thanks for the links. In case anyone else is interested here is the page with the technical info:
http://apswater.com/page38.html

[Darkfrog]

Rick,
Do you run RO in front of the DI? I was thinking of just getting a 2-stage DI using with a prefilter like the Kent.
With the high quality of Atlanta area tap water, I didn't know how long the DI carts would last, but I thought maybe the RO would be superfluous.
What's your take?

[Rick O]

Here's the order of my filters:

1) Prefilter with carbon block
2) RO membrane
3) Cation resin
4) Anion resin

Charles (C_K_Kuehne) brought his TDS meter over and tested my product water from my RO/DI and it was 16 so I figure it's time to replace the DI media. It's been about two years and the color has changed gradually and I hadn't noticed that it was used up.

He also tested my tap water and I believe it was around 61 if I remember correctly. He's been testing a lot of peoples water so he could better advise you on the need for RO but my understanding is that it prolongs the life of the DI cartridges.

[Doug1]

I suck at chem, but the RO removes the bulk of mineral salts, etc, the DI tends to remove whatever gets thru the membrane. Using a straight mixed resin DI like the Tap Water Purifier, without an RO before it, will result in greatly decreased lifespan, depending on the source water

[Darkfrog]

I do understand that the RO will improve the life of the DI, but I guess my question is how much? Like you said, "depending on the water source." Since we have relatively low TDS in our tap water (RickO got 61, most areas of the country hover around 150), won't an RO be more costly in the long run? If I run RO, I have to replace fairly expensive membranes, not to mention all of the waste water (don't tell me I can recycle it because I am going to plumb the waste line into the drain)
Also, the DI resins can be recharged fairly cheap. I just don't know how to calculate the cost:benefit of running RO first.

[Doug1]

You have valid points, if your source water isnt bad to start and you don't mind playing with hydrochloric acid and lye, using and recharging DI cartridges night be worth considering. My water is so hard and has ag runoff, I was recharging the DI after about 40-50 gallons, compared to once a year with RO in front. Since I am on a well waste water and city water bills is not an issue for me

[Darkfrog]

Originally posted by Doug1
You have valid points, if your source water isnt bad to start and you don't mind playing with hydrochloric acid and lye, using and recharging DI cartridges night be worth considering.

Hmm what's cheaper, replacing RO membranes or building a chemistry lab replete with chemical fume hood
This hobby gets me in a lot of trouble.

[DKKA]

RO membranes don't need to be changed very often. You should easily get a couple years use out of one.
I don't know if it's true, but I read somewhere that they should last indefinitly and only need replaced if they become blocked up (which would be noticed by a decrease in product water)

With your level of TDS I would think an RO membrane would last quite a while.
Of course, that doesn't solve the wastewater issue.

Dan

[tdwyatt]

Originally posted by Rick O
I need to replace my DI resin. Can someone tell me the difference in cation and anion? I have separate refillable cartridges for each.

heh, sorry, I have been out with my little daughter doing pet rescue today...

Short answer is that the cationic resins exchange protons for the positively charged half of ionic substances in the water. They unfortunately will require mostly prefiltered water to remove large polymers and organic substances to prevent their premature exhaustion by these same substances. As they are NOT a mixed resin, they must have a separate anionic resin column to remove the anions, usually exchanging hydroxyl groups for the anions. To achieve the 17 mOsm/ml level of lab water purity, they usually require a RO membrane to remove the larger uncharged molecules prior to the filtrate's exposure to the ion exchange resins. The reason these resins work is that they have been treated with either a strong acid to remove other positively charged cations from the resins and recharge the cationic resin with protons; or a strong base/alkali, which does the same but for anions and uses the hydroxyl ion to recharge the resin. The resins then have more affinity for the substances of higher electron shell need/excess (depending on the ion and its elemental status/number/etc.) As they exchange hydrogen initially and hydroxyl in the second stage, the effluent does not become charged with excessive unwanted elements/ions, but with an excess of "water" as the result of the combination of the proton and the hydroxyl group (to make H2O),

Sorry I didn't see this earlier, hope this helps.

Heck, I think of Craig Bingman when I think of Chemistry experts, I just read a lot...