In water demineralization, when I have the following anions in mixture: chloride, fluoride, nitrate, nitrite, arsenate, sulfate, phosphate, when the resin is getting saturated, what is the sequence in which they come out?
The sequence of elution on an anion exchange column should be: fluoride, chloride, nitrite, nitrate, phosphate, sulfate and arsenate.
Depends on the anion exchange resin, but if this is a strong-base resin,the most widely used one, the expected sequence in which these anion should come out is
Fluoride < chloride < nitrite < phosphate < arsenate < nitrate < sulfate
Thank you each one of you for your valuable input.
Which is the cheapest, with long life for use in rural India? or any rural area?
How can I ensure that F and As are retained most?
How does the villager know that the toxic F and As are coming out and it is time to regenerate the resin?
Pl advise. Many people are suffering Fluorosis..
Dear Bapuji Maringanti,
If you want to retain F and As, you must use F and As selective resins. For example, F selective ion exchange resin (chelating resin loaded with aluminum ions) is manufactured by LANXESS. Regrettably, these type of resins tend to be more expensive than the commonly used resins... As to your last question, the villagers cannot know that the F and As are coming out since they, only slightly if at all, are changing the organoleptic properties of the water at already toxic concentration levels... Hope this, answers to your questions.
are there insoluble indicators to detect F and As in water? That may solve the problem I raised?
There are some, but they are semi-quantitative (by comparison of color). You can consult http://www.merckmillipore.com/PT/en/product/Arsenic-Test,MDA_CHEM-117917#anchor_PI and, perhaps, if you have some further concerns, ask for help on that the responsible governmental bodies in India.
Depends on the nature of the anion exchange resin. With a strong base- resin, the likely sequence of elution should be as follows:
Flouride
Alum does not remove fluoride with any appreciable efficiency.
Can you use a conductance reading (similar to deionizer systems) that is just a light? It goes out if the resin is exhausted. You will get breakthrough of fluoride significantly sooner than arsenate or arsenite, so the ion you really want to detect is fluoride.
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