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Re: Aquatic Plants Digest V3 #674

Hello,


I wonder whether the Ani- & Kati- ion exchangers are the same ones that
were used about 20+ years ago in Germany. If I remember correctly, there
were several warnings published in DATZ regarding the leaching of the
resins.

Those Kati- & Ani- were regenerated separately by a hydrochloric acid
and sodium hydroxide solutions. Thus the cations are replaced by a H+
ion and the anions by a OH- ion  -- that's why they are in separate
columns. Theoretically, one gets an equivalent of distilled water. (by
the way, the "K" in "Kati-" has nothing to do with potassium. Cation in
German is apelled with a "K"!)

BUT, if some resins leach into the water -- and that is what was alleged
-- then the water becomes slightly toxic. It was recommended that each
day the columns are used the first two column volumes of water be
discarded, to discard all the leached material.

If the columns offered by PetWarehouse use HCl/NaOH regeneration, they
are probably the same stuff sold in Germany. Not only is the separate
HCl/NaOH regeneration of the resin a bother, it will add to the cost of
operating the system, and one has to dispose of a potentially toxic
stream. Unless the tap water is awfully expensive, I would choose a RO
system and use the discarded water for gardening, live food culture,
etc. One way or another *all* the water has to find its way to the ocean
-- or evaporate on the way!

Best,

George



> Peter writes:
> 
> > Pet warehouse recommended to use a KATI and ANI ion exchange unit, which
> >  costs almost the same and RO/DI, does not waste water, and can be
> >  recharged.  I'm told it produces even purer water than RO/DI.  Does
> >  anyone have any experience with this method, and can offer advice as to
> >  which is preferable?
> 
> The KATI and ANI unit is a 2-stage variation on DI.  The KATI exchanges
> cations of calcium, magnesium, etc. for something else, possibly either Na or
> K.  By the trade name I would assume Potassium (chem. symbol K).  The ANI unit
> then pulls out anions, like chloride and carbonate.  I suspect if forces the
> positive ions to precipitate, but I'm not an expert.  Is it better than RO?
> That's a coin toss.  It is certainly better than some DI units on the market,
> but others may be better.
> 
> Bob Dixon