Re: Used Hydrogen Peroxide for Removing Metal Stains - Resul
chem geek,
I know "I'm like a dog with a bone" or perhaps a "A bad penny that keeps coming back."
Anyway here I go again.
First some housekeeping, I made corrections regarding the incorrect mention of "organic phosphates" when I should have written "orthophosphate(s)" in the post above, thank you for pointing it out. I called "Palintest" at 1-800-835-9629, Thorium Nitrate solution does expire after 1 year, so my solution is 2 months overdue for replacement. As it is quite expensive costing about $50 from Palintest and more from Jack's, for just shy of half a liter, I might wait. As I understand it, Thorium Nitrate degrades quite slowly. The very pleasant lady said she would email me tomorrow after emailing the UK where it is manufactured to see what the time degradation amounts to in percentage per year, I will then advise in a later post. I called BASF in Hawaii, but they are not the BASF chemical company, I will work on that later.
Now onto what I have discovered.
I "Googled" many sources such as:
"Hydrogen Peroxide Degradation pH"
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1149288/
"Hydrogen Peroxide Degradation temperature"
"Hydrogen Peroxide HEDP"
http://books.google.com/books?id=QL...=hydrogen peroxide decomposition hedp&f=false
"Hydrogen Peroxide Calcium"
"Hydrogen Peroxide Wood Pulp Calcium"
http://www.tappi.org/Downloads/unsorted/UNTITLED---pulp981157pdf.aspx
"Hydrogen Peroxide Phosphates
"Hydrogen Peroxide Calcium Oxalate"
http://x.havuz.org/viewtopic.php?p=28892
http://www.amjbot.org/content/84/8/1042.full.pdf
From this I came up with some obvious answers:
It works better at a pH below 7.0, to remove iron, phosphates and other metals, all the way down into the 4.6 range, the lower the better, generally speaking. That is what I found to be true when I used Ascorbic Acid (AA). Although in many of their processes to remove metals from waste water they use Acetic Acid (vinegar) which has a pH of 4.76. In the processing of pulp they mainly use sulfuric acid, and sometimes Muriatic Acid.
And generally speaking HP works best at removing iron, phosphates and other metals, at temperatures below 70 F, and slows down rapidly at higher temperatures unless a lot of acid is used. That is maybe why I did not see such a great drop in the phosphate test on the 4th try as the pool temp was 77 F, versus around 68 F to 70 F in the 3 other treatments and my pH was 7.0.
Iron and particularly manganese are great catalysts to help us remove phosphates, this we know.
Now for the more interesting stuff:
HEDP is superior to EDTA in sequestering iron, this we know But what I did not know was that EDTA in the presence of HP will only allow HP to sequester for about 25 minutes or so before it depletes the HP (it might be the other way round - no matter it will not work), HEDP will sequester iron, phosphates, other metals, AND CALCIUM (more on that below) for about 7 to 7.5 hours if more than 13 ppm of HEDP are present.
And now for the really, really, interesting stuff:
"The Hydrogen Peroxide Method" in a pH below 7.0 (the lower the better) with HEDP in doses above 13 ppm, and in the presence of manganese (best) and/or iron, (OR IF IRON ETC ARE NOT PRESENT) IN ORTHOPHOSPHATES (IF IN SUFFICIENT QUANTITIES - quantity unknown) DOES SEQUESTER CALCIUM, CALCIUM CARBONATE AND CALCIUM PHOSPHATE to CALCIUM OXALTE
YEE-HAW!
But nobody, even the top scientists and chemists in the wood pulp industry know EXACTLY why this occurs, so chem geek you are in very good company when you stated you were not sure how this might occur. Although it is known that HP can sequester carbon and its compounds. It is actually a big problem for them as it gums up their filters removing minerals etc they do not want to remove in certain quantities. As I understand it they want to remove a certain amount but the calcium is removing too great an amount. It precipitates as Calcium Oxalate.
That is why despite the filter removing a large amount of calcium the third time I did the HP method overnight, even more went to the filter once the suction side cleaner was re-attached, it was sucking up more Calcium Oxalate crystals mixed possibly with the phosphates, and conceivably iron, which fell to the bottom of the pool. Although the second backwash was not as heavy a load.
Post-Mortem:
So it seems that while I do have iron in my pool the greater problem was created by the breakdown of HEDP to orthophosphate in such large quantities(above 45,000 ppb when it should be below 10,000 ppb), above the threshold limit mentioned in the Dow Chemical paper (see here the graph labeled - "Figure 2.12 Critical phosphate concentration under various pH at 25°C"):
http://msdssearch.dow.com/Published...8.pdf?filepath=/609-02023.pdf&fromPage=GetDoc
That it also created "Calcium Phosphate Scale", which looks a lot like iron staining. My guess is that I had a lot more "Calcium Phosphate Scale" than I had real iron stains. Certainly by the amount of what might be a form of Calcium Oxalate dumped out of the filter in the two backwashes on the 3rd try using HEDP, Ascorbic Acid and Hydrogen Peroxide. Please bear in mind I reached 35,000 when I kept the ppm of the HEDP sequestrant at a very conservative 10 ppm, only upping it to over 20 ppm when it reached that number a few months ago. The raising to the higher levels of 40, 60, and 100 ppm only occurred in the last month or so.
What does this mean for the average HEDP Sequestrant user?
Quite simply your phosphate levels will keep rising if you are a regular user and may possibly fairly quickly reach the breakpoint level if you have iron or organics entering your pool via water or wind.
YOU HAVE TO HAVE A SEQUESTRANT TEST KIT AND A PHOSPHATE TEST KIT. And you need to consult the above graph to make sure you do not go above the threshold level FOR PHOSPHATES or you might get "Calcium Phosphate Scale" Use the HP method with the AA method to lower your phosphate levels, or lower your pH to 6.9 to save money and try and see how well just the HP method lowers phosphates, remember the colder the temperature the better it will work AND ALWAYS DO IT JUST AFTER DARK. In my case with 350 ppm calcium, and a pH of 7.3 the graph says I need to keep my phosphate levels below about 10,000 ppb. Remember 1 ppm of HEDP is 1000 ppb of potential orthophosphate, so levels can rise quickly.
Does this method replace the Ascorbic Acid Method?
Certainly not, but it is a good addition to it. One point that might be worth considering is not to use Algaecide 60 in the early part of the treatment, it is not needed and might interfere with the HP treatment, but put it in an hour or so before sunrise if you are planning on continuing the AA treatment another day, to avoid the potential for algae growth. Remember by morning the HP will have been completely used up and you may need to back wash your filter as calcium may be blocking it up. Then check your sequestrant level every 2 weeks and if you have an iron problem then maybe 20 ppm will do the job, if no iron issues maybe 15 ppm. I would check the phosphate level once a month and treat if needed. Also in the AA treatment it is recommended to up the chlorine level 1 ppm per day, until the target level is reached, I think that is an excellent idea to avoid iron separation from the sequestrant, also recommended is to hold the pH between 7.0 and 7.2 for a week or so this to will avoid iron separating out.
Does the level of phosphate really matter that much:
I think by what I have personally experienced this answer is a big yes.
Now I have to go back to all the people that I have helped with their pools and tell them "Yes, you really do need to know the phosphate level in your pool. I was wrong, we learnt something new". Just as Galileo tried to tell the world that he was wrong and that the earth is not the center of the universe but revolves around the sun. It is going to hurt and sting that I thought I knew it all, and told people that I have 35,000 ppb of phosphates in my pool and I have no algae, so I have no problems. Well I was wrong, very wrong. They do matter but not in the way that pool salespeople would have you believe, but in a different way. It would be extraordinarily expense to remove these breakeven levels of phosphate with lanthium, etc based removers, not to say time consuming, the HP method offers an inexpensive and quick solution and if you do have calcium scaling it might do that as well.
How to measure large amounts of phosphates:
In my phosphate test kit it will measure up to 1,000 ppb by filling the tube to a marked level, pouring in the powder and then shaking for one minute and comparing the blue color against the enclosed color chart. To measure 10,000 ppb one would first pour 9 tube measures of pool water into a glass container, then fill the tube to a marked level with additional pool water, pouring in the powder and then shaking vigorously for one minute, adding it to the glass container stirring vigorously and pour it back into the tube and compare the color. If the color was at the 500 ppm one would multiply that by 10, you will then know your phosphate level is 5,000 ppb. To measure 20,000 ppb you would do the same only you now need 19 measures of pool water plus the one you have shaken. Multiplying that by 20, and so on and so forth for higher levels.
Other Considerations:
1. It might be necessary to repeat the combined AA and HP process a number of times as the HP exhausts itself after 7 to 7 1/2 hours, to fully remove all calcium staining. This is best done once a week but not daily I would think.
2. After you have done the process(s) to your satisfaction you may still might find you have some remaining light stains, these are probably old organic stains, for some reason neither the AA or HP seems to do a great job on these. The reasons these might appear is that they may have been hidden by the calcium scaling if it were thick enough. You could raise your pool to shock level and keep it there for a week or two and this might do the trick, but you will have to wait at least 5 weeks before doing this or you could restain the pool with metals. Or you could hold the pool at non-shock but higher levels of chlorination and this could take days, weeks, or even months. None of this is guaranteed to work if the stains have been there a very long time and you may never get rid of them.
A wish to the Forum Administrators:
Above the Dow Chemical graph is a formula for working out exactly where one should not exceed the phosphate level at a given temperature, pH and hardness, could perhaps you chem geek or someone else put this into an Microsoft Excel spreadsheet or better still include it in the "Pool Calculator".
I realize Chem Geek that you might disagree with some of what I have written so I look forward to your comments. Years ago Oxalic Acid was a recommended chemical for stains but gave poor results, then someone came up with Ascorbic Acid which is really good at lifting iron, then someone on this forum talked about Hydrogen Peroxide for iron and yes iy is OK but only with lower levels of pH and works very well with AA, and in conjunction with AA it can improve overall results. I am sure in the future someone else will find an even better method. Let us hope so.
Thank you.
