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Subject: Re: TWL: RE: reverse osmosis and salt
From: Wesley Eldred (weldred@XXX.XXX)
Date: Wed May 01 2002 - 14:53:20 EDT
Mel:
The following, from the description of a household reverse osmosis
system, may clarify the issue:
"Water molecules penetrate the thin layer of the reverse osmosis
membrane and diffuse through it
molecule by molecule. Dissolved salt ions would also diffuse through
this layer, except that the
solubility of the salt ions in the membrane is much less than that of
the water. Thus, the water
moves through more rapidly with the result that a separation occurs. The
driving force is furnished
by both the pressure and the concentration differentials across the thin
layer.For water, the
pressure effect is the most important. Therefore, increases in pressure
increase the water flux
without a corresponding increase in salt flux."
It would appear that some salt does pass and how much depends on system
pressure.
Wesley
weldred@XXX.XXX
"hknott4@XXX.XXX" wrote:
>
> ..REVERSE OSMOSIS watermakers (not evaporative ones, which aren't so bad)
> remove enough salt for the water to be palatable, but it's not all the
> salt. The resulting water is much more conductive at the voltages found
> in the water heater...
>
> Very interesting, Keith. Although I don't have a watermaker, I was under the impression that they produced water that was close in chemistry to deionized water... that in a properly functioning one, the membrane allowed the passage of the water molecules, but not the salt molecules, period. That there was no "in between" or "only removes some of the salt."
>
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