I am using Ion Exchange Resins (Anions and Cations) for the very first time and upon carrying out a little research on it, I found out certain terms and processes that I will need anyone with some experience to through practical light on them.
1. how is regeneration carried out?
2. is backwashing the same as deionization, either ways how are these processes carried out? (seen some discussion on whether to use brine or bleach)
3. are there any pre-treatment methods, that enhance usage apart from just wahing with DI water?
Dear Sir. Concerning your issue about the best methods to regenerate, backwash and de-ionize Ion Exchange Resins. an ion-exchange resin in industrial use is usually regenerated every 12 to 48 hours. Depending on the use of the resin, this can be done in several different ways, each with their own advantages and disadvantages depending on both chemical and economic factors. Complete deionization (i.e. demineralisation) can be achieved by using two resins. The water is first passed through a bed of cation exchange resin contained in a vessel similar to that described for softeners. This is in the hydrogen ion form brought about by the use of a strong acid regenerant (either hydrochloric or sulphuric). During service, cations in the water are taken up by the resin while hydrogen ions are released. Thus the effluent consists of a very weak mixture of acids. The water now passes through a second vessel containing anion exchange resin in the hydroxide form for which sodium hydroxide is used as the regenerant. Here the anions are exchanged for hydroxide ions, which react with the hydrogen ions to form water. Such twin bed units will reduce the total solids content to approximately 1-2 mg L-1. The backwash cycle expands the resin bed from its settled and packed condition, and cleans the resin by flushing out any suspended solids that may have been filtered during the service run. Resin particles can act as effective filter media because they have ionic charges, which can coagulate fine particles. During the backwash, the resin beads rub against each other, and this scrubbing action helps clean accumulated dirt or iron from the surface of the beads. The backwash flow also removes any broken resin particles or resin fines. In addition, the backwash cycle classifies the bed with the larger resin beads on the bottom and the finer resins on top. This provides the best conditions for a good uniform flow of brine, rinse and service. I think the following below links may help you in your analysis:
https://nzic.org.nz/ChemProcesses/water/13D.pdf
https://www.wqpmag.com/resin-regeneration-fundamentals
http://www.academicjournals.org/article/article1379433623_Al-Sabti.pdf
Thanks
Really appreciate your input Sir, Isam Eldin Hussein Elgailani. Will go through the materials as well. Thank you.
Regards
Ion exchange is a phenomenon based on concentration gradients.
Typical ion exchange resins have a working capacity of 1equivalent per liter of resin. The idea is to create a driving force strong enough to reverse the original attraction.
- Backwash removes suspended solids. You can have a very well filtered feed stream and use a counter current service/regen mode packed bed for better kinetics.
- For strongly acidic and basic resins, you need to provide 2-4 equivalents of counter ion (H+ or OH- or Na+ or Cl-) within about 2 bed volumes at 0.25 -0.33 gpm/ft3 resin. You typically end up with a 5% acid or caustic solution. In case of softeners, saturated brine at 10-11% is used.
- For weak acid and weak base resins, you need to just provide enough counter ions to neutralize the resin. Thus these resins regenerate with very little excess chemical. Typically 20% more than stoichiometric requirement.
- A slow rinse cycle removes chemical from resin bed. Typically 3-5 bed volumes of a slow rinse at maybe 0.33 gpm/ft3 of resin is usually required.
- A fast rinse of service flow rate, 2-4 bed volumes reclassifies the bed, and removes residual chemicals, making bed ready for service.
- Packed bed counter current regenerations are slightly different, and can end up saving quite a bit of chemicals.
Hope this helps.
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