Removing metals from water

[BlueWave8]

I am considering doing an AA treatment to (hopefully) remove some of the staining on my plaster pool. I am still trying to grasp an understanding of the process, but from my reading so far it appears that an AA treatment removes metals from plaster and suspends them in water via a sequesterant. Am I correct in thinking that these metals are not really removed by normal filtration? You have to keep adding sequesterant to keep them from redepositing on the plaster? Or until you drain the pool? How often would sequesterant need to be added to keep metals in solution? To me at least, it seems like we should be able to come up with a better solution...

I think that the metal staining in my pool is from the Carribean Clear system that was used by the previous owner for around twenty years. From what I can determined, the water has never been changed. I'm not crazy about draining the pool because a) I have a well and b) I have a well. a) refilling my pool would put a large demand on my well and I am unsure of the well's ability to meet that demand and b) I don't exactly have warm and fuzzy feelings about emptying 15,200 gallons of chlorinated water containing metals into my yard as I don't know what effect this would have on my groundwater.

So...

Since the chlorine level for an AA treatment is supposed to be 0 anyway, would some kind of carbon filtration be effective at removing metals suspended in the water? If so how much carbon would be needed and with what kind of exposure time? Would the type of sequesterant make a significant difference in how the carbon removes the metals from the water?

 

[JasonLion]

There are various ways to remove the metals but none of them work reliably and affordably. Some sequestrants will sometimes cause the metals to clump and be filtered out. Shocking can also cause that sometimes, though shocking runs the risk of redepositing the stains on the pool. In most cases the best you can do is to add a little more sequestrant weekly.

 

[BlueWave8]

Does anyone know from experience (or other) if carbon filtration works reliably?
This paper (attached as a PDF) would seem to suggest that it does, but my chemistry background isn't sufficient to digest it fully, as I am not sure what forms of copper are staining my plaster or what they would be in solution.

 

[tcm]

I was reading a post earlier that chemgeek had posted about a product called CuLator. He was asking if anyone had ever tried it before. I searched but there never was any follow up on this. I looked, the product sold at Amazon and a couple of other places. If the stuff works as advertised it would be great, "if" being the key word there. It's not cheap but not extremely expensive either. It may be worth a look considering there are not a lot of options out there for removing the metals.

 

[Pb2Au]

The CuLator product is a bag you add to the skimmer, They have 2 kinds one will remove 0.8 ppm of metal from 20,000 gallons of water. The other claims it is heavy duty and it will remove 1.0 ppm from 20,000 gallons. This product does remove the metal, not sequester or chelate it. Of course it can take up to a week or even two for it to work. www.periodicproducts.com.

 

[BlueWave8]

So this bag would be used after an AA treatment? Would sequesterant still need to be used?

 

[chem geek]

Yes, you would use this after an AA treatment since the CuLator will only remove metal ions circulating in the pool and will not do anything for existing stains. As for whether you need to use a metal sequestrant, that depends on how likely it is for the stains to return as chlorine is added and the pH goes back up. If that is likely, then add a metal sequestrant. The CuLator will remove metal ions even from a metal sequestrant since a sequestrant doesn't completely bind to all metal ions -- it's an equilibrium. So as metal ions are adsorbed in the CuLator more is released from the sequestrant, just like the chlorine/CYA equilibrium, and this happens quickly.

If you try this out, I suggest you get a metal ion test done after the ascorbic acid treatment (and sequestrant, if used) to see the level you are starting with. Then after using the CuLator for some time, especially after one month, measure the metal ion concentration again and also make sure there aren't new stains (which could cause the metal ion concentration to drop). That will tell you if the CuLator removed the metal ions. You should also be able to see the bag get somewhat colored and after you remove the CuLator you can open the bag and see the white pellets being colored instead. Most metals will color these pellets if the are adsorbed to them (see this link).

 

[BlueWave8]

Thanks for the response, Richard.

Could you suggest a reliable metal ion test? (I would like to stay away from strips at any reasonable cost. I feel the same way toward bromates and salinity)

As for the carbon I mentioned above, would this be an effective way to remove the metals in question? If it is close to or as effective as the CuLator product is supposed to be, then that would be ideal as it would be significantly less expensive. (Depending on how much metal a certain amount of activated carbon could adsorb...)

 

[JasonLion]

The carbon is going to be ridiculously expensive. It will absorb all kinds of things from the water, not just metals, and get saturated with stuff quickly. You would need a huge amount to get a significant amount of metal out of the water.

Taylor makes good metal tests. K-1716 for iron and K-1730 or K-1738 for copper.

 

[chem geek]

Yeah, if by carbon you mean activated carbon, that removes all chlorine from the water as well and I didn't think activated carbon removed iron (unless oxidized as particles, but then any reasonable filter will remove iron oxides that have precipitated). That is not a good option. An ion exchange system would work, but would be prohibitively expensive and painful (lots of recharging) for pool water volumes. Smaller metal filter systems are OK for filling spas, but pools have so much volume of water that such systems are generally impractical. You can read about various iron removal techniques in this link. For large volumes such as for pools, manganese greensand filtration is probably a reasonable option when fill water is high in iron.