Deionizing Resin replacement time. Which to use?

[HighlandReefer]

Its time for me to order DI resin. This time I want to use a re-fillable canister. I have used the standard Mixed bed color changing DI resin filter up to now. I currently have a zero reading with my in-line TDS meter. I have had to replace the DI filter about every 6 months.

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Looking at the resins online leads to some questions:

ANION SILICA RESIN REFILL. My well water contains a lot of Mica. The general formula for minerals of the mica group is XY2–3Z4O10(OH, F)2 with X = K, Na, Ba, Ca, Cs, (H3O), (NH4); Y = Al, Mg, Fe2+, Li, Cr, Mn, V, Zn; and Z = Si, Al, Fe3+, Be, Ti.

MIXED BED COLOR CHANGING DI RESIN REFILL vs non-color changing. I have an in-line TDS meter. I never pay much attention to the color anyway.

SEMICONDUCTOR GRADE DI Resins: what is this?

Mixed Bed DI vs Separate Bed DI Resins? Randy mentioned in his RODI article that the Separate Bed DI resins are slightly better.

Separate Bed Resins are broken down into: DI Anion Resin & DI Cation Resin?

I am afraid to look into this any further. :lol:

[Yogre]

Hi Cliff,

I'd like to tag along, I figure you're going to get some responses I'll learn quite a bit from.

I personally am a big fan of the refillable cartridges. I use the Bulk Reef Supply non color-changing mixed-bed resin, and have been very happy with it. I have 2 DI carts in series, and while I haven't kept a detailed log, I seem to get a few hundred gallons of H20 before the second cart will start showing 1 ppm TDS.

I don't know the makeup of my well water in detail, other than to say TDS is high (>350 ppm), and NO3 and PO4 are also quite high.

[HighlandReefer]

I will be interested in the theory of using two DI cartriges (even though I don't seem to need one). Possibly several possibilities of different DI resins recommended in this scenario?

[Yogre]

I'm pretty sure Randy uses 2 DI carts, using a staggered replacement interval. I can't remember how the sequencing works... the procedure may be on one of the vendor websites, I think it might be SpectraPure.

I have to use 2 DI carts, if I don't I have to replace the single cart too quickly. Russ from Buckeye Field Supply told me I probably have high CO2 in my water, which I guess significantly shortens resin life.

Since you don't have that problem, you could get some interesting combos going that would last awhile...

[bertoni]

If you're using the inline meter, then there's no point in bothering with the color-changing media, which aren't all that reliable, anyway. The semiconductor grade might be rather expensive; I don't know much about it.

The mixed bed is more convenient, in general, and the performance difference shouldn't be critical. The dual mixed bed allows replacing the first cartridge in line when it begins to fail, which would still leave the second cartridge to produce clean water. Probably I'd then rotate the second cartridge to the first position.

[tmz]

Yes. I run mine pretty much that way. Two di canisters with an in line tds meter between them. When input for canister 2 goes over 0ppm, I change out canister one and rotate them.
This method protects your system . Randy notes that phosphate and slica may be more loosely bound than other things the resin takes up So a very low tds post di can be quite harmful.
The in line meter let's you know when to change it out avoiding premature changes.

[HighlandReefer]

Well, I found an article which seems to anwer my questions. I thought I would share it. I think I will just stick with the mixed bed with no color change indicator: ;)

Deionized Water (DI)
http://www.cal-water.com/pdf/DI_in_a_NutShell.pdf

From this article:

"DEIONIZATION IN A "NUT SHELL"

City water is passed through dark amber colored, caviar sized plastic beads called cationion exchange resin. The cation resin is in the �ghydrogen�h form (H+) and exchanges all thepositively charged ions for hydrogen, thus converting all the impurities in the water intoacids.

The acidic water from the cation is then passed through tan colored, caviar sized plastic beads called anion ion exchange resin. The anion is in the �ghydroxyl�h form (OH-) and exchanges all the negatively charged ions into the hydroxyl form, thus completing the conversion of all impurities into water (H+) + (OH-) ----> H2O, thus providing pure deionized water.

DEIONIZATION IN "DETAIL"

Dissolved Solids - Ions

In nature solid inorganic substances dissolve in water and ionize into separate positive and negative components or �gions.�h These ions, whether positive or negatively charged, are known as electrolytes because they conduct electricity.
A good example of ionization is what happens to table salt when it is added to water. What was solid NaCl becomes the positively charged cation, sodium [Na+] and the negatively charged anion, chloride [Cl-]. The Greeks gave these disassociated electrically charged substances the name �gion�h which means `to go about', which is exactly what they do. In water, the Na+ goes one way and the Cl- goes another.


Ions Commonly Found in City Water

Cations:
Sodium [Na+], Calcium [Ca++], Magnesium [Mg++], Potassium [K+], Iron [Fe+++], Manganese [Mn++] and Hydrogen [H+]
Anions:
Chlorides [Cl-], Sulfates [SO4=], Nitrates [NO3=], Carbonates [CO3=], Silicates [SiO2-] and Hydroxyl [OH-]

Ion Exchange Resins
Modern science has developed materials commonly called �gion exchange�h resins. These resins take the form of little plastic beads made out of styrene cross-linked with divynalbenzene. Once formed, the beads are then either cooked in sulfuric acid to provide negatively charged sulfite sites to make cation resin, or processed in an ammonium salt solution to provide positively charged quaternary ammonium sites for
anion resin. It is the charged sites on these resin beads that give them their ion exchange properties. It has been estimated that a cation resin bead half a millimeter in diameter contains more than 280 billion exchange sites.

Cation Resin
The sulfite sited cation exchange resin is regenerated with an acid solution. In the acid form (H+), cation resin removes positively charged impurities such as calcium (Ca++), magnesium (Mg++), sodium (Na+) and potassium (K+). The impurities attach themselves to sites on the ion exchange resin, eluting off hydrogen (H+) from the acid regeneration. The resultant liquid is a mixture of acids caused by the association of the H+ hydrogen ion from the resin with all the anionic impurities still in the water.

Anion Resin
The resins with the quaternary ammonium sites are called anion resins and are regenerated with caustic soda solution to put them into the hydroxyl [OH-] state. The anion resin is then able to remove negatively charged impurities such as chloride (Cl-), sulfate (SO4=) and carbonate (CO3=). The impurities attach themselves to sites on the ion exchange resin, eluting off the hydroxyl radical (OH-).

Deionization
At this point all of the exchangeable anions and cations that were in the water are now held on the cation and anion resins exchange sites. The hydrogen ions [H+] eluted off of the cation resin combine with the hydroxyl ions [OH] eluted off of the anion resin to form pure water.
[H+] + [OH-] �¨ H2O
This process continues until the resins have a majority of available exchange sites taken up with impurities. When this happens the resin is said to be exhausted. But after the cation resin is treated with acid and the anion is treated with caustic soda the deionizer is ready to operate again. The ability of ion exchange resins to be regenerated and used over and over again makes it a very practical and economical water purification tool.

Cation Regeneration
As soon as all the sites on the cation resin have given up their H+ ion and have taken up cationic impurities, the resin must be regenerated. To regenerate a cation resin column, a 10% hydrochloric acid (HCl) solution or a 4% sulfuric acid (H2SO4) solution is passed through the cation resin. The concentration of hydrogen ions in the acid solution provides the driving force to remove any other cations from the resin in favor or the hydrogen ion (H+).

Anion Regeneration
When the anion resin is loaded up with anionic impurities it is regenerated by passing a 4% caustic soda (NaOH or KOH) solution through it. The concentration of hydroxyl ions in the caustic soda solution provides the driving force to remove the anion impurities from the resin in favor of the hydroxyl [OH-] ion. The resin is once again ready to play its part in deionization.

Separate Bed Deionization

Separate bed or two-bed deionization refers to the fact that the cation resin and the anion resin are in separate tanks. Regeneration is relatively simple, and water quality is frequently around 200,000 ohms/cm3 or 2 ppm.
Info 2

Mixed Bed Deionization

In Mixed bed deionization the cation and the anion resins are mixed after regeneration and placed in the same vessel. The purpose of mixing the resins is to achieve a very high quality deionized water. When the resins are mixed, as the water passes through the resin bed it encounters a cation resin bead, then an anion resin bead, then cation, anion, cation, anion and so forth. The water is deionized then re-deionized continually resulting in an ultra high purity product.
The regeneration of a mixed bed resin complicated by the fact that the resins must first be separated into cation and anion columns, separately regenerated and rinsed, then mixed again. This process is more expensive and difficult than separate bed regeneration and mixed bed capacity is typically significantly lower than separate bed deionizers. But the product water from a properly regenerated mixed bed is the highest quality obtainable. Mixed bed deionization will frequently yield a water quality exceeding 18 megohms, less than 25 parts per billion.

Selecting a Deionizer System

It is important to select the proper deionizer for a specific need. In general the higher the quality of the deionized water required, the higher the cost. It is best to choose the most economical system that will meet your requirements."

[tmz]

Here is a quoe from Randy's article on ro/di which notes post di tds may be particluarly bad:

"...Also note that the first impurities to leave the DI resin as it becomes saturated may be things that you are particularly concerned with (such as ammonia if your water supply uses chloramine or silica if there is a lot in the source water..."

[HighlandReefer]

Yea. I read about hobbyists who let their TDS reading climb up to several ppm before they finally change their DI resins. What they don't realize is that the first things to escape into the final effluent of their RODI water when the TDS readings start to climb are the stuff they least want in their tank, like the ammonia from the chlorine and particularly the chloramine. These things are just dumped in large quantities very quickly. :eek1:

If I notice that my TDS reading hits 1 ppm, I dump the entire container of my rodi water reservoir. I have well water and do not have to worry about the chlorine or chloramine but I do have to worry about the silica which is released easily in large quantities. ;)