I've been thinking about copper...

[thilbert]

Some time this week a post was made about copper in poolwater. The general consensus was that once there, it's impossible to remove unless you drain the pool.

This got me to thinking about using the principles of electroplating to remove copper from poolwater. So I fire up google and perform a search on "Copper removal" and found a page by a young college guy who was doing experiments with copper.

After briefly viewing his page, I fired off this email:

Tim,

I am a pool owner that has a slight problem as it relates to copper and upon
trying to discover a permanent solution to copper disolved in pool water, I
came upon your site.

Folks tell me that there is no way to permanently remove
copper from pool water. They tell me that I can bind it up so that swimmers
won't get green hair; however it is a very temporary fix.

If the bather load in the pool is high, at the end of the swim it is typical to
"shock" the pool with large amounts of chlorine (I use 6% laundry bleach for
this purpose) which then causes the copper to precipitate out of solution. Thus leading one to add a chemical to bind it up again. Catch-22.

I am hoping you can tell me if there is a way to permanently remove copper
by electrolysis and if there is, would you be so kind as to describe how to go
about it?
------------------------------------------------------------------

And I recieved a prompt reply

(next post...)

[thilbert]

> I am hoping you can tell me if there is a way to permanently remove
> the copper by electrolysis and if there is, would you be so kind as
> to describe how to go about it?

Yeah, you could hook up a 5V supply to a couple of electrodes, minding that the positive will corrode so you want to use something corrosion-resistant like sheets of solid graphite (probably not terribly cheap). Copper will plate out on the cathode (negative).

The pool guys probably say you can't because either there's a constant source, or there simply isn't enough to remove it from solution. Even copper metal has some solubility in water, and concievably a lot could dissolve in a whole swimming pool. And that's just pure water; you have all kinds of salts and chlorine and stuff to keep it clean. The chlorine tends to oxidize copper to cupric ions, usually a deep green (concentrated) or light blue (dilute) color
(probably easy to miss against water's normal blue color). Especially if the
pool is acidic, you could hold a lot of copper in solution.

The other problem is the source. First of all, what did it come from? Copper
plumbing? I'd bet it's still there, so to fix it, you need to fix the cause,
too.

So lemme see... you can try to find a stronger, insoluble complex. EDTA (lemme see if I remember that, ethylene diamine tetracetate, yeah think so) is used to complex heavy metals in food and blood, to help prevent spoilage or cure heavy metal poisoning. You should be able to dump in a few ounces or pounds, run the filter and see if that clears it up.

Other ways to remove copper are to raise the pH, precipitating copper hydroxide as a green or blue sludge (if it isn't present as a complex that's soluble in basic pH!), or to add a reducing agent (such as sodium sulfite) that converts it to cuprous ions, or metallic copper. Cuprous ions are less soluble and will precipitate as either white cuprous chloride (which turns green in moist air because it would rather be the oxidized form!) or yellow to orange to brick red cuprous oxide, otherwise known as the mineral cuprite.

Tim
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This seems promising so I fired off another email to Tim

(Next post...)

[thilbert]

Tim,

Thank you very much for the quick response.


---- Tim Williams wrote:
>Yeah, you could hook up a 5V supply to a couple of electrodes, minding that the positive will corrode so you want to use something corrosion-resistant like sheets of solid graphite (probably not terribly cheap). Copper will plate out on the cathode (negative).

Not being a trained chemist / scientist, would both the anode and cathode
consist of graphite? By the way, I think I can find a relatively cheap source
for solid graphite: fishing rods / golf clubs (OK maybe not the latter). What
type of amperage are we talking here? I am assuming that you are talking about DC, yes? This is, perhaps, the most promising solution for reasons I state below.


> The pool guys probably say you can't because either there's a constant source, or there simply isn't enough to remove it from solution. Even copper metal has some solubility in water, and concievably a lot could dissolve in a whole swimming pool. And that's just pure water; you have all kinds of salts and chlorine and stuff to keep it clean. The chlorine tends to oxidize copper to cupric ions, usually a deep green (concentrated) or light blue (dilute) color
(probably easy to miss against water's normal blue color). Especially if the
pool is acidic, you could hold a lot of copper in solution.

No, there is no constant source. This winter, our outdoor fire pit (copper
bowl) got blown into the pool. I didn't realize it until very recently. I am
positive that this is the source as all the pool plumbing is PVC. And it's true
that the pH of the water was slightly acidic over the winter (about 6.8 or so). I noticed the green effect when I began to open the pool: adjust ph to ~7.2 and dumped in a boat load of 6% bleach, in effect getting about 20 ppm of chlorine to kill off algae (this level of chlorine was maintained for about a week). At first, I thought it *was* the algae, but as the shocking continued, the pool cleared up but stayed green. I am guessing that since I brought the pH into nominal for pools and then dumped in the chlorine the copper precipitated out of the water and attached itself firmly to my pool liner.


> So lemme see... you can try to find a stronger, insoluble complex. EDTA
(lemme see if I remember that, ethylene diamine tetracetate, yeah think so) is used to complex heavy metals in food and blood, to help prevent spoilage or cure heavy metal poisoning. You should be able to dump in a few ounces or pounds, run the filter and see if that clears it up.

I googled EDTA and it turns out that the main component of "Metal Out",
mentioned previously, is EDTA with a twist, MSDS lists its chemical name as:
Ethylenediaminetraacetric Acid Tetresodium Salt. Salt being the difference.
Could this possibly cause the chemical in "Metal Out" to be weaker than other
sources? The problem here is that even though this works, it's temporary as
indicated in my earlier email. As I understand it, my pool filter (diatomaceous
Earth) filters particles no smaller that 5 microns when clean and presumably
when EDTA binds with the copper in solution the particles are smaller than I can filter. Can you shed light on that?


> Other ways to remove copper are to raise the pH, precipitating copper
hydroxide as a green or blue sludge (if it isn't present as a complex that's
soluble in basic pH!), or to add a reducing agent (such as sodium sulfite) that
converts it to cuprous ions, or metallic copper. Cuprous ions are less soluble
and will precipitate as either white cuprous chloride (which turns green in
moist air because it would rather be the oxidized form!) or yellow to orange to brick red cuprous oxide, otherwise known as the mineral cuprite.

Yes, this is my experience. Unfortunately it precipitates right onto the liner
of my pool and no amount of scrubbing takes it off.

As you can see, this is a perplexing problem for pool owners and someone could make a mint off of a permanent solution. Which of course leads me to believe that a.) there isn't one and b.) it's too expensive for pool owners. Of the two, I have to think "a" is the answer because we spend WAY TOO MUCH money in general.

So, having bored you to death by now, a method to remove the copper via
electrolysis seems to have some promise.


Tim,

Thanks again for taking the time to help me solve a problem pool owners have been dealing with (unsuccessfully -- as in not permanent) forever. I truly appreciate the effort, especially considering we are total strangers. It's
great to live in the information age, where a guy looking to fix his pool can
get advice from an expert.

Best regards,

Troy

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His response follows

[thilbert]

The cathode can be a generic piece of sheet metal, non galvanized. Or
copper, or better yet, titanium, but I doubt you have any of that on hand

> By the way, I think I can find a relatively cheap source for solid graphite: fishing rods / golf clubs (OK maybe not the latter).

- Not the right form. Those are carbon fiber, which may or may not be
graphite as such. The usual form is a slab of industrial graphite. A
single crystal slab would probably be even better but would be just a bit
more expensive...if even produced.

> What type of amperage are we talking here? I am assuming that you are
> talking about DC, yes? This is, perhaps, the most promising solution
> for reasons I state below.

Ya, probably 10 amps. You want more surface area and circulation than you
do current. The problem you'll have is running out of copper atoms to
remove from a given volume of solution around the electrodes.

> No, there is no constant source. This winter, our outdoor fire pit
> (copper bowl) got blown into the pool.

Hmm, seems to me that couldn't possibly provide much copper, unless the
whole thing disappeared... I might be underestimating the strength of colors, though. (Potassium permanganate for instance makes solutions so strong you can see parts per million in solution!)

> I didn't realize it until very
> recently. I am positive that this is the source as all the pool plumbing
> is PVC. And it's true that the pH of the water was slightly acidic over
> the winter (about 6.8 or so).

Eh, I don't know that that's enough. But I don't have a pool, either.

> I am guessing that since I brought the pH into nominal for
> pools and then dumped in the chlorine the copper precipitated out of the
> water and attached itself firmly to my pool liner.

That could certainly do it. I've ran experiments where copper compounds
precipitated on the plastic container wall. Glass is much better for the
most part. Not that that helps you any.

> I googled EDTA and it turns out that the main component of "Metal Out",
> mentioned previously, is EDTA with a twist, MSDS lists its chemical name
> as: Ethylenediaminetraacetric Acid Tetresodium Salt. Salt being the
> difference.

Ah, that'll do fine, too. You also see calcium disodium EDTA a lot. I
should've mentioned, all that matters is the EDTA molecule is there and not
attached to anything stronger than it attaches to the things you want to
remove (copper or iron in this case). It does form a salt with sodium and
calcium, but it doesn't complex with them nearly as strongly as with iron or
lead.

> Could this possibly cause the chemical in "Metal Out" to be
> weaker than other sources? The problem here is that even though this
> works, it's temporary as indicated in my earlier email. As I understand
> it, my pool filter (diatomaceous Earth) filters particles no smaller that
> 5 microns when clean and presumably when EDTA binds with the copper in
> solution the particles are smaller than I can filter. Can you shed light
> on that?

I would think the stuff would make the ions precipitate, but if there are
few ions in solution, I suppose it would be kind of hard for the molecules
to clump together and form large particles.

> Yes, this is my experience. Unfortunately it precipitates right onto the
> liner of my pool and no amount of scrubbing takes it off.

You might be able to rub it off with a mild hydrochloric acid solution. Use
lightly around grout, if any. Don't really know how you could do that
without draining the pool, though.

> Thanks again for taking the time to help me solve a problem pool owners
> have been dealing with (unsuccessfully -- as in not permanent) forever.

You're welcome.

Tim

[thilbert]

> The cathode can be a generic piece of sheet metal, non galvanized. Or
> copper, or better yet, titanium, but I doubt you have any of that on hand

I found a pure commercial grade titanium basket for $44:
http://www.coleparmer.com/catalog/pr...sp?sku=5940100

Do you think this would be sufficient for the cathode?

> - Not the right form. Those are carbon fiber, which may or may not be
> graphite as such. The usual form is a slab of industrial graphite. A
> single crystal slab would probably be even better but would be just a bit
> more expensive...if even produced.

I also found a pretty good resource for industrial graphite. It's surprising
that it can be had for so cheap!
http://www.andale.com/store?view=CAT...=176000&mode=1

What I was thinking is to get the titanium basket and put the graphite in the
center of it, Apply electricity and wait. What do you think?

> Ya, probably 10 amps. You want more surface area and circulation than you do current. The problem you'll have is running out of copper atoms to remove from a given volume of solution around the electrodes.

10 AMPS?!!!?!????!!!?? Wow. Would a reduction in the amount of amps cause a significant performance penalty? My pool pump can recirculate the entire contents of my pool about 5 times a day, therefore I don't think that I would run out of copper atoms.

> Hmm, seems to me that couldn't possibly provide much copper, unless the whole thing disappeared...


It was a rather big bowl. I would say about 4 feet in diameter. Lot's of
surface area.


Would electrolysis work to also remove the iron in my pool using the same
materials (graphite and titanium)? If not, what should I use?


Here is the process I am considering taking:

1.) Drop pH to 6.8 -- any more and I risk damaging pool components (pump etc.)
2.) Add citric acid to bring iron into solution.
3.) Add EDTA to bind up the Iron and Copper
4.) Insert electroplating device into pool
5.) Test copper and iron levels regularly

Plausible? Or should I just live with the copper?


Thanks again,

Troy

[thilbert]

> I found a pure commercial grade titanium basket for $44:
> http://www.coleparmer.com/catalog/pr...sp?sku=5940100
>
> Do you think this would be sufficient for the cathode?

Hmm, that would be pretty nice.

> I also found a pretty good resource for industrial graphite. It's
> surprising that it can be had for so cheap!
> http://www.andale.com/store?view=CAT...=176000&mode=1

Hmm, be nice if they had cheaper though (i.e. no need for +/-0.005"
tolerance or tighter!).

Surface area is what reacts, so you need to maximize surface area,
especially with such a large volume of water. For the same reason, you need
to circulate the water pretty quickly, too.

> 10 AMPS?!!!?!????!!!?? Wow. Would a reduction in the amount of amps cause
> a significant performance penalty?

I don't know, it depends on how much copper is available for the electrodes
to remove. You could probably get away with an amp or less, especially if
your pump is slow.

Relax, 10 amps at 5V is only 50W. Your computer monitor consumes double
that.

Remember you're adjusting voltage to change current. You'll need a variable
power supply of some sort, and an ammeter. Remember to keep the connections
out of the water, especially on the anode side, else you'll defeat the whole
purpose of using graphite in the first place

> My pool pump can recirculate the entire contents of my pool about 5 times
> a day, therefore I don't think that I would run out of copper atoms.

I don't know about that. I'm thinking you'll be able to remove "all" the
copper roughly around the electrodes (maybe, ehrr.. 10 gallons worth?) in a
couple minutes, so you'd want the water flowing through, as systematically
as possible, to remove the copper.

In fact, the best solution might be to pump all the pool's water through a
section of 3" PVC pipe containing the apparatus. If you somehow have
another pool to empty the processed water into, you can systematically
process the entire pool without the cleaned product diluting what's there,
slowing the process down a lot.

> It was a rather big bowl. I would say about 4 feet in diameter.
> Lot's of surface area.

Ah, then that could do it.

> Would electrolysis work to also remove the iron in my pool using the same
> materials (graphite and titanium)? If not, what should I use?

It might, if the iron is in solution. Again, insoluble stains are best
treated with, well, stain removers...

> Here is the process I am considering taking:
>
> 1.) Drop pH to 6.8 -- any more and I risk damaging pool components (pump
> etc.)
> 2.) Add citric acid to remove iron in pool
> 3.) Add EDTA to bind up the Iron and Copper
> 4.) Insert electroplating device into pool
> 5.) Test copper and iron levels regularly
>
> Plausible? Or should I just live with the copper?

I would skip the EDTA, since you want the copper freely available for the
electrolysis.

Oh- one thing I forgot to think of, graphite tends to erode under
electrolysis. It shouldn't be a problem if you keep current density low,
but if you see black stuff flaking off that doesn't want to filter very
well... you might want to try a different method!

Tim
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I am drawing up some plans to build a device to do this. For those of you who are experts here, what do you think. Does this sound like something that is doable?

Drawbacks?

Troy

[waterbear]

> I googled EDTA and it turns out that the main component of "Metal Out",
> mentioned previously, is EDTA with a twist, MSDS lists its chemical name
> as: Ethylenediaminetraacetric Acid Tetresodium Salt. Salt being the
> difference.



Tim

Some thoughts:

EDTA is a the chelating agent that is used as the tritrant in the calcium hardness test (reagent #3). It complexes with the calcium (or metals) in the solution. The complex is a large molecule but to filter it out the question becomes how fine a filter medium do you need. Some type of millipore filter medium might work.

There is also a material called poly filter
( http://www.poly-bio-marine.com/ )
that is used in water purification and aquarium use that is very efficient at removing copper. Perhaps this might be an easier experiement to try. Filtration through active carbon first would help remove the chlorine which might interact with it. I have much first hand experience with using this product to remove copper from aquarium water when it has been used for treatment of ick.The main problem would most likely be cost since quite a lot would probably be required to filter a pool! might be an intersting route to try!

[thilbert]

The complex is a large molecule but to filter it out the question becomes how fine a filter medium do you need. Some type of millipore filter medium might work.

I agree; however DE filters can handle about 5 microns, what else can handle a better level of filtering and not cause pressure issues (obviously using only your pool equipment)

The main problem would most likely be cost since quite a lot would probably be required to filter a pool!

Cost is, to me, a deal breaker. I was looking for alternative methods to negate that factor. I think that, providing it works, that I can build this for a (relatively) small cost and it can be re-used.