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

The order of elution of divalent / trivalent ions is dependent on the ionic strength of the feed, the nature of the resin and the level cross-link. At a certain cross over point, sulfate usually comes out first close to chloride on strong anion exchangers. The order of elution is little hard to predict in your case. Fluoride is least retained.

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.

Dear Bapuji, Lot of work has been done to remove fluoride and arsenate by low cost adsorbents/ coagulants rather than expensive resins. Can the villagers use tried and tested alum to clean the water? Alum can remove fluoride to some extent as well. Please read these:

http://www.epa.gov/ncer/events/calendar/2013/aug13/lawler.pdf

http://www.sswm.info/sites/default/files/reference_attachments/HERING%20ET%20AL%201997%20Arsenic%20Removal%20from%20Drinking%20Water%20During%20Coagulation.pdf

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.

Thank you all again. MrFarooq: I will be in Houston from end Feb for a few months visiting my daughter. Can I see your labs? Pl give your details to [email protected].