Deionizing resin to remove iron?

[TreeFiter]

I have posted several times about a pool with serious iron staining, and how I have been trying to remove the stains with products like the CuLater. It just so happens that the tenant renting this house for the summer is a chemist who knows a fair amount about water treatment. So needless to say, this pool has become a bit of a science experiment, and has started many interesting discussions about pool chemistry. The other night, I was talking to him, and he brought up the idea of a dionizing resin. I had never heard mention of this, and I'm wondering why this isn't something used to remove Iron from pools. My guess is that it just gets too expensive, but for people with iron problems, pouring money into chemicals that don't really get rid of the iron can get pretty expensive as well.

So is there a reason deionizing resins won't work for pools?

 

[Patrick_B]

Typically, softener resins are made to exchange salt and hardness, and even though they will catch a fair amount of some Iron forms, it isn't their primary purpose. In time, they become fouled with Iron and lose some (or a lot) of ability to exchange salt and hardness as well as they did. There are specific exchange media that target Iron, such as Greensand, but it's not commonly used. Completely removing Iron from water is not as simple a process as removing hardness, but systems exist, and can absolutely be used for that purpose.

 

[stev32k]

Resin will work very well. It is used to produce ultra high purity water for high pressure boilers and laboratory use. In addition to removing iron it will also remove Calcium, Magnesium, and other cations. The draw back is that it's very expensive and you need to monitor and adjust pH as the cations are removed. It's been many years since I last bought any resin, but the price used to be in the range of $200 per cu ft. The resin needs to be monitored and replaced or regenerated as it gets depleted. It's capacity to remove iron is limited depending on how much is used and the type so you have to measure the iron levels into and out of the resin to know when it's time for replacement or regeneration.

I have a feeling that the cost might be prohibitive for a residential pool.

 

[TreeFiter]

Resin will work very well. It is used to produce ultra high purity water for high pressure boilers and laboratory use. In addition to removing iron it will also remove Calcium, Magnesium, and other cations. The draw back is that it's very expensive and you need to monitor and adjust pH as the cations are removed. It's been many years since I last bought any resin, but the price used to be in the range of $200 per cu ft. The resin needs to be monitored and replaced or regenerated as it gets depleted. It's capacity to remove iron is limited depending on how much is used and the type so you have to measure the iron levels into and out of the resin to know when it's time for replacement or regeneration.

I have a feeling that the cost might be prohibitive for a residential pool.

Do you have any idea how much iron one cu. ft. might remove?

I have a feeling you are right about the cost being prohibitive, at least for most people. In the long run, it might break even, but most people shy away from the lump sum investments even though they will be cheaper in the long run.

 

[Richard320]

Treefiter, did you happen to catch this thread: Just got Taylor-2006 Test Kit. Want to verify what I should add.

Check out the pictures in 8 and 9.

 

[TreeFiter]

Treefiter, did you happen to catch this thread: Just got Taylor-2006 Test Kit. Want to verify what I should add.

Check out the pictures in 8 and 9.

I haven't seen this one specifically, but I have seen a few posts regarding home made iron traps. Very clever, but I think with these filters, only the oxidized (insoluble) iron is being picked up. Sometimes this gets most of it, since we add strong oxidizers like chlorine to the water, but the situation I'm dealing with is a bit different.

Its really kind of interesting. The pool was a nightmare, and nobody could figure out how to clear it up. Finally it landed in my lap, and I got it straightened out. Strange things were happening in this pool. The pool guy before me knew the pool had a history of iron problems, so he tried to "fix" them with a sequestrant. The sequestrant caused all of the calcium to precipitate, and cloud the water. So I approached the cloudy water as an algae issue, and it didn't seem to get much better until I blind vacuumed the pool and saw that in the middle of this pool was a pile of white (saw it coming out the waste line). We stopped using the sequestrant, and a few days later, the pool started to clear up. Then we saw that the entire liner was orange. So we hit it again with the sequestrant, which did lift the iron stains, but it turned the water cloudy again due to the calcium precipitate. This was how we figured out that it was the sequestrant causing the cloudiness. At that point I started looking for other ways to deal with iron. We never had the typical greenish or rusty looking water. We barely had a rusty backwash. The iron just kept coming back on the liner.

I found out about the CuLater, and decided to try that along with a citric acid treatment. Citric acid treatment would lift the stains, but even with the CuLater, they keep coming back. I have seen the CuLater work in other pools, but for some reason, this pool just doesn't want to cooperate. The other really strange thing about this pool is that we have never been able to get a positive result for iron when tested. The only explanation I have found for this is that the iron I am seeing is within Iron Bacteria. The bacteria is staying on the liner, and isn't really in the water, so it doesn't show up in any tests. I'm not sure I'm convinced of this, but I'm currently trying a different approach that was reccomended by the people at CuLater to kill the Iron Bacteria and free up the iron so the CuLater can remove it. There is a post on TFP somewhere discussing the same issue. It sounds like they were successful in that case.

Anyway, this long and painful journey with this one pool has brought about numerous conversations and brainstorming sessions about how to get iron out of a pool. The most recent one took us down the path to Deionizing Resins. I don't think it will fix the problems I've had with this particular pool, but it would be nice to find a few options that might work for normal iron situations.

 

[stev32k]

Do you have any idea how much iron one cu. ft. might remove?

I have a feeling you are right about the cost being prohibitive, at least for most people. In the long run, it might break even, but most people shy away from the lump sum investments even though they will be cheaper in the long run.

Unfortunately the resin capacity does not depend on iron alone, but on the total exchangeable ions in the water and on their ionic state. The water would need to be tested by the resin manufacturer (or an analytical lab) to determine which resin to use and how much would be required to get rid of the iron. There are many different resins and they vary widely in cost, efficiency, and capacity. It could be that a regular water softener would work in your situation, but testing would still be needed to find out.

 

[TreeFiter]

Unfortunately the resin capacity does not depend on iron alone, but on the total exchangeable ions in the water and on their ionic state. The water would need to be tested by the resin manufacturer (or an analytical lab) to determine which resin to use and how much would be required to get rid of the iron. There are many different resins and they vary widely in cost, efficiency, and capacity. It could be that a regular water softener would work in your situation, but testing would still be needed to find out.

I'm starting to see why this isn't commonly used for pools. It sounds like its not something the average homeowner would be able to handle.

 

[chem geek]

Probably more practical in terms of filtration of iron is a greensand filter. It is composed of glauconite greensand with a special coating of manganese oxide that oxidizes manganese and iron when in contact with the filter. It is used as a pre-filter before filling. The filter is backwashed to remove the iron and it is regenerated with potassium permanganate. However, as I noted, this works best as a pre-filter BEFORE chlorine is added to the water because chlorine will oxidize the iron.

By the way, as for your CuLator experiment, let us know how it works out and if you run into any trouble contact the company. As you pointed out, this thread described special procedures adding copper to the pool to kill iron bacteria and then using CuLator to remove both the iron and the copper which worked for that user (doubleOKevin).

 

[stev32k]

By the way chem greek's post reminded me that chlorine is a bad no-no when using an ion exchange resin. The resin is easily oxidized by the chlorine and will be destroyed at even low chlorine concentrations. So nearly all resin systems use a carbon filter in front of the resin to remove any traces of chlorine.