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Pink tinge to sodium hypochlorite solution

Pink tinge to sodium hypochlorite solution

Pink tinge to sodium hypochlorite solution

(OP)
At one of our plants we are regularly seeing a pink tinge or worse in our sodium hypochlorite solution. The chemical is tankered in from a supplier , but the same supplier and often the same tanker goes to our other plants and the problem is not apparent there. The solution in the tank has a slight yellow color about it as usual but when we collect a sample from the dose pump manifold bleed point it often has a pink or red color in the solution. We thought for a start that the hypochlorite had leached the color out of the thread seal tape but this has been happening for some time now.
Does anyone have a suggestion about the cause of this?

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

RE: Pink tinge to sodium hypochlorite solution

Not mentioned is the materials of construction of your hypochlorite pumping system. Review and compare the materials of construction. For example, corrosion of stainless steel will generate rust and an off color.

RE: Pink tinge to sodium hypochlorite solution

I've known iron contamination to make this type of coloration which is maybe what bimr is alluding to. The pdf I attached has a graph relating color to iron concentration. This link has an interseting cause identified for this family of solutions, maybe it can provoke a eureka moment? Have you locked down all the phenolphthalein? lol

RE: Pink tinge to sodium hypochlorite solution

(OP)
Thanks for your response.

The system comprises of an opaque PE storage tank located in a enclosed dark climate controlled room maintained at about 23 degrees C. The pipe work is very similar to what we use in our other plants, grey UPVC with chemical service PVC ball valves and fittings mostly in the 25mm or 1 inch size. Any flexible connections are made using tubing and fittings supplied by the dose pump manufacturer's in this case Grundfos. We do not see a constant pink stream but merely a cup full from the sample point off the end of the suction manifold. If you drained it today it might be a day or two before you would see it again. Sometimes it can be quite red other times just pinkish. The hypo in the tank is not discolored.

We have no control over the manufacture of the sodium hypochlorite solution as this is supplied from a plant about 3 hours away. All of our plants have been supplied by the same manufacturer for more than 10 yrs.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

RE: Pink tinge to sodium hypochlorite solution

Do you occasionally get pink sodium hypochlorite downstream of the pump after the contamination builds back up or is it always confined to the suction side sampling point?

RE: Pink tinge to sodium hypochlorite solution

(OP)
I have never seen it but it is a closed dosing system so you would rarely get the chance to see the chemical.
The sampling point is on a short dead leg maybe 100mm /4 inches or so.

The pink tinge does not settle out if left to sit.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

RE: Pink tinge to sodium hypochlorite solution

Hard to say what the cause it if everything is non-metallic. Maybe there is a piece of metal or debris that was left in the pipe when the system was constructed.

RE: Pink tinge to sodium hypochlorite solution

(OP)
Just as a follow up we submitted samples to a lab today and may have some results in the next few days. The trouble is we don't know exactly what to look for.
I also had a discussion with one of the top guys at the manufacturer of the hypochlorite. I have known this guy for many years and he has been in the business longer than i am old. He said he had never seen or heard anything like this, but he is guessing that it will be a metallic substance that is causing the issue.

However lets see what the lab turns up.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

RE: Pink tinge to sodium hypochlorite solution

Do the other sites take samples at the equivalent location in the same frequency and haven't seen the problem or have they not checked?

RE: Pink tinge to sodium hypochlorite solution

I would look for metals first- ICP spectroscopy is sensitive and economical. If the culprit is organic it can be a tiny trace causing the color and identification very tricky. Good luck, and do let us know if you find out.

RE: Pink tinge to sodium hypochlorite solution

(OP)
Some sites would check occasionally, and has never been an issue.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

RE: Pink tinge to sodium hypochlorite solution

(OP)
Just an update on this.

We have collected samples and sent them to two different labs for testing.
One is testing the hypochlorite and one is going screen for various metals and organics.

The lab doing the work on the hypochlorite has come back and said its normal, in terms of strength and chemical constituents , pH, SG etc.

We will have to wait and see what the other lab comes up with.

The problem appears to have gone away however.

Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

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