Help - Hypochlorites effects on chelating towers

[lenin_yuweh]

I need help.

In my work place (we mainly treat copper contaminated water), our downstream are pointing the chlorine content of our water for the cause of their copper concentration going up after the waste has gone through their chelate towers. This chlorine content shows no visible indication in the water so it's tough to point out.

The hypochlorites comes from the downstreams scubber towers which mainly cleans the air of HCl fumes. They put liquid chlorine to remove the smell and the water goes to us mixing it with acidic waste water containing [Cu] less then 1000ppm.

The question is, can hypochlorites disable the chelate resins to release the copper instead of absorbing the copper? Also, at what concentration of hypochlorites does it happen?

We have hypochlorite concentration ranging from 600 to 5 ppm. We used Metabi sulfite to treat the hypochlorite and hydrogen peroxide content in the waste that causes floating slurry. However, we only specify the flowrate and concentration of metabi sulfate solution for hydrogen peroxide and not for hypochlorite.

To test the hypochlorite concentration, we use a pack test which my supervisor said is not reliable since it can also detect Cl- and Cl2. Also, using the low grade and high grade of ClO- pack test shows different results. This maybe due to ClO- being really sensitive.

Additional to that question, can Cl- and Cl2 also disable the absorbing abilities of the chelate resins? Is there a more reliable testing to be done to check the hypochlorite content?

 

[chemisttree]

I don't see how hypochlorite could hurt the resin unless the levels are extreme. Remember that the ion exchange resins exchange all positive ions. If you introduce a source of sodium (as in sodiummetabisulfite or sodium hypochlorite) the sodium will happily exchange with copper to some degree. Same is true if the pH is lowered by adding liquid chlorine (Cl2). It forms hypochlorous acid... the proton can exchange with the copper as well. It depends on the nature of the chelate resin.

Dow has developed relatively pH-insensitive resins (http://www.dow.com/liquidseps/prod/pt_cu.htm" for example) that are better suited for that situation.

 

[lenin_yuweh]

From what I understand with our downstream's chelate towers, it only absorbs the Cu2+ ions and not exchange ions with the waste. They said that since hypochlorite is an oxidixing agent, it makes the resins release the copper ions already absorbed by the resins. I find it dubious considering what reaction would happen between Cu2+ and ClO-.

Our currently solution being done (which is causing us more sweat, tears and money) is to accept that hypochlorite does weaken the absorbing power of the chelate towers. Also, we have to add AgNO3 in the solution. If it reacts, my boss said that there's real Cl when using the ClO- pack test. Which really is confusing. Does he mean that Cl causes the weakening of the resin?

 

[chemisttree]

Your test with silver tests for chloride as well as some other anions. It isn't specific for hypochlorite at all. You are measuring Cl^-.

The resin might be 'specific' for copper but if a little hypochlorite can cause it to release the copper, it isn't specific at all.

Find out what resin they are using in the chelate tower.

 

[dadgad]

Lenin
I did my PhD on hypochlorite chemistry ( a good while ago now). We tried to modify its reactivity by letting it interact with transition metals chelated in macrocycles. Some of these macrocycles bind the metal so strongly that you can stabilise extreme oxidation states such as copper (III). We thought they would act as catalysts to add specificity to hypochlorite oxidation. Didn't work! In every case the hypochlorite destroyed the macrocycle and dumped out the metal, usually as an insoluble oxide/hydroxide. So it wouldn't surprise me that hypochlorite affects your ion exchange resin. The ligands that were most affected were those with R-NH or R-OH groups and it might be that ether groups R-O-R would be more stable. So find out what's in the ion exchange resin. One suggestion for a solution might be to warm the hypochlorite containing water: my memory is that temperatures over 60C cause it to dissociate.
Hope this helps!

 

[lenin_yuweh]

Wow! Thank you dadgad, that really helps. From the information I got downstream, the chelating resins are a styrene-divinylbenzene copolymer introduced iminodiacetate.

The structure is basically a R-COONa.

Added question, do reducing agent such as sodium metabisulfite affect the chelating resins as well? Considering oxidizing agent affects the resins as well.

 

[chemisttree]

...the chelating resins are a styrene-divinylbenzene copolymer introduced iminodiacetate.

The structure is basically a R-COONa.

Actually the structure includes a secondary amine which can react with active chlorine to make a chloramine. I think it will happen at any level of chlorine or hypochlorite.

If you consider the reactions:

Cl2 + H2O ----> HOCl + H+ + Cl-

HOCl <------> H+ + OCl-

OCl- + H2O2 -----> H20 + Cl- + O2

You can see that adding chlorine to water followed by hydrogen peroxide leads to oxygen (froth) and chloride which you measure with your AgNO3 test. If excess peroxide is added, you consume the excess with metabisulfite. If not enough is added you have residual hypochlorite which is passed downstream to the chelate towers.

 

[dadgad]

Lenin,
I agree with chemisttree that hypochlorite is likely to attack an iminodiacetate. One of the problems is that hypochlorite solutions usually end up as mixtures of hypochlorite ion, hypochlorous acid, hypochlorite radical, chlorides, hydroxide, chlorate, and dissolved chlorine. If one of them doesn't get you the others will! I was very glad to finish my PhD and go on to something 'simple' - like analysing radical reactive components in crude oil fractions!

There is a manual at http://www.dionex.com/en-us/webdocs/4296-OnGuard_DataSheet_V28_rele.pdf that discusses uses of Dionex resin that may be similar to yours. In the references there is a paper Adam, Luke C.; Gordon, Gilbert.
“Direct and Sequential Potentio-metric Determination of Hypochlorite, Chlorite and Chlorate
Ions when Hypochlorite Ion is Present in Large Excess”. Anal. Chem. 1995, 67, 535–540, which I suspect may be relevant.

On your second question I wouldn't expect mild reducing agents to affect the resin.

 

[lenin_yuweh]

Would you happen to know what would be the specific effect of chlorine to the chelate resins? Is it the formation of CuCl2 that would result to high Cu of the treated water of chelate? According to the manual for the resin my supervisor read, the effect of chlorine interchanges the selectivity of the metal ions.

Common Cu > Ni > Zn > Co > Cd > Fe > Mn > Ca
Cl- is highly present Cu > Ni > Co > Zn > Cd > Fe > Mn > Ca
(SO4)2- highly present Cu > Ni > Cd > Zn > Co > Fe > Mn > Ca

Is it possible that the ClO- would also react with the binded copper in the resin to form cucl2?
We use a pack test for checking of ClO-. Is it possible that it will also read the Cl-?
Would metabisulfite neutralize Cl-?

Here is the confusing part. Which would affect the chelate resin? Cl- or ClO- or both? Is Cl- considered as an oxidizing agent?

Added info, the downstream team only regenerate their resin with HCl and not with NaOH anymore so now their resin is in the H form, not Na form. What is the advantage of using the Na form resin as compared to H form resin?

 

[dadgad]

The chlorine/hypochlorite will attack any OH or NH bonds in the resin, as in chemisttree's post above. If copper is chelated to the resin it will probably be forced out of the chelate, either as a soluble chloride or an insoluble oxide/hydroxide.

Cl- (chloride anion) is not an oxidising agent (remember its in common salt!) and would not react with the resin as far as I could tell. I can't comment on your test pack or your regeneration procedures - you need to go through these with your team and also with the resin manufacturers. Someone needs to do a short basic controlled programme of tests to see what is actually happening. If you don't have in-house facilities, then a local university might help. hope this helps!

 

[lenin_yuweh]

Thank you for all the help.

We're coordinating with the downstream team to have a small-scale experiment with a mini chelate tower model. We're waiting for the downstream teams evaluation. Hopefully, the small-scale experiment will bear positive responses.

Our team is running around in circles trying to figure out the causes of the abnormal increase in copper discharged after sandfilter(I posted another thread about reaction within the sandfilter that may cause brown discharged) and chelates considering our discharges shows no visible diviation from normal specs nor out of specs copper concentration discharged to the downstream. Hopefully our downstream would be more cooperative instead of just pinpointing our system immediately without proof or even research.

Thank you again.