j_sum1
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Swimming pool oxidiser question
Is there any good reason why sodium percarbonate is not commonly used as a pool oxidiser?
AIUI, it is an adduct of sodium carbonate and hydrogen peroxide. It is already in common use in all manner of cleaning products and it seems to me
that it would fulfill the requirements of swimming pool maintenance quite well.
In my corner of the world the most common pool recipes are NaDCCA as oxidant and a combination of sodium bisulfate and sodium bicarbonate or carbonate
as a pH buffer. I know there are variants including bromine compounds for spas and peroxide/HCl systems in public pools; which avoid the issues of
chloramines.
I have recently discovered that percarbonates are sold to clean cartridge filters and do a good job of breaking down a lot of the oils that enter the
system. I cannot think of a good resson that some or all of the chlorinated compounds could not be substituted with, essentially, peroxide.
Any thoughts?
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paulll
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I often wonder what criteria were used to choose peroxide over chlorine or vice versa for a given application.
In this case I'd imagine that in solution and bathed in UV light, peroxide would just do its business and piss off a lot quicker than chlorine. But I
know significantly less about pool chemistry than the people at my local hardware store(s) probably assume, I'm just conjecturing.
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Fery
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Reduce water contamination? H2O2 decomposes to H2O + O2, it is considered to be "green" reagent. Na percarbonate decomposes to Na carbonate which
occurs naturally like ca carbonate from limestone -> hydrogencarbonate.
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paulll
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Quote: Originally posted by Fery  | | Reduce water contamination? H2O2 decomposes to H2O + O2, it is considered to be "green" reagent. Na percarbonate decomposes to Na carbonate which
occurs naturally like ca carbonate from limestone -> hydrogencarbonate. |
And further to that, although there are specific,"ph boosters," the onus seems to be on keeping on the acidic side so something that's going to wind
up alkaline after serving its purpose would have to be pretty compelling.
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Sulaiman
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there may be a dosing complication,
TCCA is used because it decomposes slowly even in sunlight.
sodium percarbonate would (I think) immediately decompose into hydrogen peroxide and sodium carbonate solution,
then the peroxide would be in relatively high concentration and may bleach/oxidise/corrode paint, pump turbine, piping and joints etc.
and it will also be quickly decomposed by sunlight.
I guess dosing intervals may be quite short (relative to TCCA) so more effort would be required.
CAUTION : Hobby Chemist, not Professional or even Amateur
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j_sum1
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pH of a chlorine pool rises over time: as Cl2 is produced it consumes H+. This means that regular acid additions need to be made as well as oxidiser
additions.
Carbonate is added periodically to maintain the buffer.
For reasons I am not really sure of, it is considered beneficial to have at least 120ppm of bicarbonate ions to protect the plumbing. Likewise, CaCl2
is added to keep Ca levels around 200ppm. This protects mortar and plaster. Not sure why it is recommended for polymer or fibreglass pools. Other
common additives are algecides: I use benzalkonium chloride.
So, nothing inherently wrong with sodium percarbonate per se. It just needs to have acid additions to balance pH.
I did do a quick test. I added a little sodium percarbonate. It seemed to have a large effect on pH and seemed to have only a minor effect on
oxidative potential. I did not test the water beforehand, so my observation is indicative only. I will try again, but I think I can see why it is not
used.
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paulll
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"I guess dosing intervals may be quite short (relative to TCCA) so more effort would be required."
Was what I was going for. Where a peroxide would be chucking out oxygens for minutes or hours, a chlorine agent can be serving up chlorides for hours
or days. Weekly vs daily.
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