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Mixed bed De-ionization: How to regenerate, rinse, & separate cation resin from anion

Q. When we do regeneration of Cation and Anion resin, final step is rinsing of resin with water to adjust its desired ph with slow and fast rinse..
My question is that in counter flow regeneration method either this slow rinse and fast rinse will be in same direction as with regeneration or on opposite direction?
Means if we add regenerant from bottom and leave from top, then slow rinse and fast rinse also follow same direction from bottom to top or rinsing should be done from top to bottom?

Muhammad basit
Student Employee - Karachi pakistan
August 11, 2023

Q. My question is that, as mentioned many experts that use salt water to separate Cation resin from Anion Resin. I have tried same but in a concentration of 25% NaCl solution Cation sinks better in the bottom but Anion resin does not move upward 100%,some Anion also sink in the bottom with Cation resin as well.. how can i achieve 100% separation of Anion resin from Cation resin??? What should I do?

Muhammad basit [returning]
Student Employee - Karachi pakistan
August 17, 2023

⇩ Related postings, oldest first ⇩

Q. I am an operator of a mixed bed deionizer (MBD). Since the mixed bed resin is so expensive I intend to regenerate the resin but according to the expert the resins must be separated then each will be regenerated with acid and caustic. My question is how to separate both resins? Is there a device or methods how to do it?. FYI before this MBD are cation and anion then followed by activated carbon. The TDS of incoming water to MBD is about 10 ppm
And finally the TDS out from MBD is zero. But the life time is too short. Is there something wrong to my cation and anion which are regenerated with HCl 5% and NaOH 4%? What is the normal TDS of output? Resin vol. by cation is 50 lt, anion is 50 lt and MBD is 25 lt.
Please your kind help.

Prima Mitrau
operator - Jakarta, dki, Indonesia
June 23, 2010

simultaneous replies

A. It is my understanding that the resins have a different density, so they use salt water of a concentration where one resin will float and the other one will not.

I think that your regeneration chemicals are not strong enough. The manufacturer can give you guidance on this.

Are you aware that you need to do considerable rinsing with very good quality water to remove the trash ions with the residue of the chemical.

You rarely will get as good a life out of a regeneration that you do compared to a professional regeneration.

Talk to your vendor about training aids that you can get from them or the OEM.

James Watts
- Navarre, Florida

A. MB resins are separated by careful, upflow fluidization in a separator vessel with one or more sight glasses. Since the anion resin has a lower density than the cation resin, it will be at the top of the fluidized bed and can be sluiced off to a separate vessel for regeneration. The two resins are usually slightly different color, so it is possible to see the separation in a sight glass. Next, the cation resin is put in a separate vessel and regenerated.

Typical chemical use is 6 lbs of acid or caustic per cubic foot of resin at a strength of 4-6 %.

After regeneration and rinsing , the resins are recombined into a single vessel, remixed by bubbling compressed air through them (with minimal water above the surface of the resin), and then transferred back to the service vessel.

It is a little difficult to do this without the proper equipment.

Lyle Kirman
consultant - Cleveland Heights, Ohio

thumbs up sign Dear Sirs,
Thank you very much for your kind help.

Q. 1. I could separate them with a lot of difficulties, but it's done well. After they are separated I just regenerated it by immersing in different bowl which are already with HCl of 5% and NaOH of 4%, stirring them slowly for 20 minutes then rinse until pH is normal(6). I will be mixing them and I will see the result soon.
2. Here sometimes it's not so easy to get the right information from the maker, because they don't have it too. Or we got it but it doesn't work at all. So we have to find another way like what I am doing right now.
3. My question is: To regenerate the cation (50 ltr resin) after the back washing step I just prepared the regenerant (water 4 ltr + 1 ltr HCl of 30%) and suck into the bed by vacuum system, then after all is in wait for 25 minutes then start rinsing and stop if the TDS of effluent is already equal or less then TDS of the input water. Then the same steps are done for anion. Is this ok ?
Thank you Sirs.

Prima Mitrau [returning]
- Jakarta, Indonesia
July 18, 2010

Can't separate anion and cation mixed bed resins

Q. Hi. I am a student of engineering physics and I have to research about wire cut di resin regeneration.

I had a sample of those kinds of resins and I tried to separate the anion and cation by using their density differences: I threw it in a bottle of water but all of them sank in to the bottom!
Why did it happen? Please help me.

mitra gh
- iran, karaj
August 20, 2014

A. You increase the specific gravity of the water with salt to a point where only one resin floats. Voila-separation.

James Watts
- Navarre, Florida

thumbs up signThanks a lot dear James Watts, it worked :)

mitra gh
- karaj, iran

A. There is also usually a controlled resin bead size that facilitates the separation. The most common method to separate the resins is a carefully controlled upflow backwash and to verify the separation visually.

Lyle Kirman
Consultant - Cleveland Ohio USA

A. Use 25% NaCl solution by weight at 25-30 °C.; the lighter resin will float in this concentration.

gregorita mae
- rosario cavite, philippines

Q. Can we use direct compressed air line to mix resins in mixed bed, instead of air blower?

mp mishra
- gandhidham, India
April 13, 2016

A. The function of using air blower in resin mixing process is to utilise the big air flow which makes the mixing more efficient.

If we introduce compressed air line directly to the vessel that will make tunnels through the resin by force of the air pressure which means bad resin mixing, in addition to the possibility of causing crushing for the resin.

Ismail Rawashdeh
Takreer - Amma Jordan
October 10, 2016

A. Either compressed air (hopefully oil-free) or a blower may be used to mix mixed bed resins after regeneration. For best results, you should have minimal water above the level of the resins when mixing.

Lyle Kirman
Consultant - Cleveland Heights
December 12, 2016

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