Cool. I am going to read through that stuff and try to learn some more.
From my limited knowledge I was under the impression that when you mix
an acid with sodium chlorite the reaction is pretty well instantaneous,
regardless of which acid is used. However it makes chlorous acid, not
chlorine dioxide. The the chlorous acid converts to chlorine dioxide,
the rate of conversion being something close to being proportional to
the concentration squared. Now, thinking about it, it seems that adding
the two teaspoons to 8 ounces of water first is not correct, they should
be added together first with no dilution to get as much conversion as
possible. That could be part of the problem.
Another thought comes to mind as well. Since the rate of conversion
goes up dramatically with concentration of chlorous acid it is possible
that the rate is dependent on the level of chlorine ions and not
chlorous acid specifically. In that case the use of hydrochloric acid
adds additional chlorine ions and that might increase the conversion as
well. So maybe if one were to use citric acid, but add some additional
sodium chloride, the conversion might go up as well. This is all
supposition and will require experimental testing to confirm or deny.
I hope I can test for chlorine dioxide levels after reading the
materials, of so, then I should be able to give information that is
conjecture but rather experimentally confirmed.
I do have a HACH scanning photospectrometer, so maybe I can use it to
get some very good information, if I can figure out how to calibrate it
for chlorine dioxide. Maybe I can use the test strips for calibration,
they may not be as accurate as desired, but once I have a calibration
point, it will all be relative.
Marshall
poast wrote:
Hello Marshall,
They are actual measurements.
Here is a link to a label for a sodium chlorite/chlorine dioxide product.
You should begin to get a feel for the difference between available and free
chlorine dioxide in solutions.
http://www.sanivex.com/pdf/EPA_Label.pdf
There are a lot of variables involved with mixing, so we usually use theory
to get into the ballpark, and then adjust according to actual measurements.
I have found the Brix scale in a refractometer is an accurate way to
determine the concentrations of citric acid and sodium chlorite solutions.
A calibrated PH meter is used to monitor the activation process, and from
that information tables can be produced to estimate the amount of free
chlorine dioxide released during the activation. Unfortunately these tables
are proprietarily so they are very difficult to find.
Free chlorine dioxide is best determined with a colorimeter, but they do
make test strips that give a very good approximation of what you have. I
believe LaMotte makes them in the 0 - 10 PPM and 0 - 500 PPM ranges. Please
note that these are different than chlorine test strips.
Just to touch on the general rules...
Sodium chlorite powder is only 80% pure. This means that you have to mix a
6.25% by weight solution to end up with a 5% sodium chlorite solution.
Sodium chlorite solutions activated with acids only yield about 60% of the
available chlorine dioxide. This means that a 5% sodium chlorite solution
that should have 50000 PPM available chlorine dioxide actually only ends up
having 30000 PPM available for use.
In general, activation with 10% citric acid will result in about 10% of the
available chlorine dioxide released as free chlorine dioxide. The proper
activation ratio when using 10% citric acid is 1:1, and the optimum
activation time is 10 minutes.
In general, activation with 50% citric acid will result in about 20% of the
available chlorine dioxide released as free chlorine dioxide. The proper
activation ratio when using 50% citric acid is 1:5. That is 1 part 50%
citric acid to 5 parts sodium chlorite. Once again the optimum activation
time is 10 minutes.
Activation with HCl is a little different. The concentration of HCl needs
to be 1.2 times the concentration of the sodium chlorite you are going to
activate. This means that if you have 5% sodium chlorite you would use 6%
HCl. The activation ratio is 1:1, and the activation time is under 30
seconds. HCl drives the PH of the sodium chlorite low enough to release all
of the available chlorine dioxide as free chlorine dioxide.
Those are some of the basics. From there you can explore a number of
possibilities and design a disinfecting system that fits your needs.
Chlorine dioxide can be used to stabilize bacterial growth, or it can be
used to kill off the bacteria. In water purification it is used as a
biocide whereas in food processing it is used as a biostat. In general,
chlorine dioxide technology deals in biocide applications and acidified
sodium chlorite technology deals in biostat applications.
Tom
----- Original Message -----
From: "Marshall Dudley" <[email protected]>
To: <[email protected]>
Sent: Saturday, March 27, 2010 7:25 PM
Subject: Re: CS>Sodium Chlorite and Nail Fungus
Please advise. Are the numbers you give below actual measurements, or
computed theoretical numbers? Where did you get the information that
only about 10% will convert under those conditions? Can you refer me to
a paper, or url which discusses this? I was unaware of the incomplete
conversion with weak acids, and if correct, then you are correct that
the use of citric acid would be ineffective. If you actually measured
the chlorine dioxide content, can you tell me what instrument or
protocol you used?
Marshall
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