We have a well that delivers hard water and we do not have a water softener. (There was a “green sand filter” that utilizes permanganate to oxidize other metals on the system, but it has been disconnected.) Analysis of the well water shows the presence of iron in noticeable amounts. No other metal ions were specifically identified. The system does have an ozonator to oxidize Fe(II) to Fe(III). Over the last couple of years, the porcelain toilet bowls have developed a blue ring at the air/water interface. When you scrub on the blue ring, it doesn’t feel like there is a deposit present (like normal hard water deposits). The ring is unresponsive to ammonia (household), strong acid (6 M HCl) or strong base (Drano), as well as to hydrogen peroxide (30 %). (We haven’t tried a good reducing agent yet.) So, my question is, does anyone have an idea of what is causing the blue color? Is it possible that porcelain reacted chemically with salts, urea, uric acid, oxygen, etc? Not an earth-shattering theoretical question, but I’m chemically curious as to what this could be if anyone has any ideas.
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I know this may seem silly...but I've spent several hours looking up information on colored salts, colored complexes, and trying to find out some information about the reactivity of porcelain and nothing has been useful. And the site has been asking for more questions..... – Janice DelMar May 11 '12 at 05:15
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are you in NC or Georgia? – Chris May 11 '12 at 10:34
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I'm actually in California. – Janice DelMar May 11 '12 at 15:07
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1The blue color is copper from some copper or brass plumbing, presumably. The "bulk" of the deposit is SiO2 (hydrated), doped by Copper. – Georg May 15 '12 at 12:52
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@Georg, if this is the case then why is there only a blue ring? – Chris May 15 '12 at 22:07
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@JaniceDelMar, do you know the pH of your drinking water? – Chris May 15 '12 at 22:10
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1I second the idea that the blue is from copper. What part of California do you live in Janice, the Valley? Very hard water around there. – Pat May 16 '12 at 01:49
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@Chris The pH of our drinking water is 6.7 pre-ozone and 7.4 post ozone and the ozonator is currently on most of the day. I live in Sonoma county. Copper pipes are supposed to be less prone to corrosion when in hard water, so would there be appreciable copper ions present? And how do they dope the porcelain under such mild conditions? (Do you have any references? I can't find anything relevant.) I've used porcelain crucibles and spot plates with various salts and not had discoloration under much harsher conditions. Thanks for any ideas. – Janice DelMar May 16 '12 at 05:36
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What about some silikate in Your water? My idea is some silikate deposit, not copper in the porcelain enamel (which is not possible). Copper does not come from pipes, but more from taps, esp. perlator mesh at water/air interface. – Georg May 21 '12 at 21:40
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@Georg If it is a copper (II) silicate deposited on the porcelain, shouldn't it be soluble in strong acid? We've tried 6M HCl on it without effect. Is there a simple test you know of that could confirm your suggestion that it's a copper silicate? Thanks. – Janice DelMar May 28 '12 at 06:12
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Electronics people sometimes use ferric chloride to etch copper off PCB blanks. I hope your freshly oxidized Fe(III) ions aren't slowly etching away your plumbing! – Bernd Jendrissek Jul 13 '12 at 20:55
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As just a quick tip - it could be some kind of ferrous chelate (cyanide, aminoacidic) ? – java_xof Jul 20 '12 at 12:07
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Have you tried mixing hydrogen peroxide with sulfuric acid in the bowl? Powerful etchant. – Chris Jul 24 '12 at 06:20
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I found these instructions: Copper Stains: Combine one cup of white vinegar with 1 tbsp of salt and boil until the salt dissolves. Then dip a cotton rag or towel in the liquid and place directly on top of the copper stain. I repeated this process twice and got rid of ALL our copper stains. – Thawn May 25 '16 at 19:03
2 Answers
Toilet bowls are made of ceramics which can contain feldspar. Toilet bowls also often have a feldspar glaze. There is a study that disolved Cr(VI) can be removed by feldspar.
Studies on the removal of Cr(VI) from waste-water by feldspar http://onlinelibrary.wiley.com/doi/10.1002/jctb.280530204/abstract
The IMA currently recognizes 90 Cr bearing minerals. 16 minerals if you only count those that contain also Si. Feldspar can be either K, Na or Ca-Feldspar. Of those 16 minerals 6 contain Na, 2 K and 5 Ca. Reading those papers might even narrow the choices down to a couple of minerals that can form in standard-toilet-bowl-conditions.
Mineral database that lets you select minerals by their chemistry: http://rruff.info/ima/
I think that unless you are willing to donate your toilet bowl to science that the answer won't get any more precise than this.
Edit: Cu would be the favorite choice for a blue color mineral (Azurite, ...). There is also a study about the removal of copper by feldspar:
Experimental studies of the interaction of aqueous metal cations with mineral substrates: Lead, cadmium, and copper with perthitic feldspar, muscovite, and biotite http://www.sciencedirect.com/science/article/pii/S0016703797001178
Again there are 603 Cu-minerals. Cu+Si=32 minerals. With the common Feldspar cations your left with about 10 each. I don't think the minerals could be recognized visually. The favorite method would be x-ray diffraction of a powder sample of the blue stuff.
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Thanks for the information..now I need to take some time to go through it. It would be nice if there were some simple solubility tests to ascertain whether this approach has merit...without sacrificing the toilet bowl to science. (Although maybe when redecorating time rolls around....) An interesting idea, at any rate. – Janice DelMar Sep 13 '12 at 03:47
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XRD of a glaze will not yield any results as glazes are glasses, not crystalline. – A.K. May 22 '16 at 05:02
I heard it is a high acid content in the water which is eating away at by he copper pipes. The copper turns blue when oxidized like the statue of liberty, the copper residue stains the toilet bowel. This was very rare until fracking started.
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