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How to separate cation resin from anion in a mixed bed

June 23, 2010

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

simultaneous June 23, 2010

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

June 24, 2010

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, Ohio

July 18, 2010

Q. Dear Sirs,
Thank you very much for your kind help.

1. I could separated 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%, steering them slowly for 20 minutes then rinse until pH 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 other way like what I am doing right now.
3.My question is : To regenerate the cation ( 50 ltr resin ) after the step back washing I just prepared the regenerant ( water 4 ltr + 1 ltr HCl of 30%) and suck into the bed by vacuum system, then after all in wait for 25 minutes then start rinsing and stops if the TDS of effluent is already equal or less then tds of the input water. Then the same steps done for anion. Is this ok ?
Thank you Sirs.
Prima Mitrau

Prima Mitrau [returning]
- Jakarta, Indonesia

Can't separate anion and cation mixed bed resins

August 20, 2014

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 21, 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

August 22, 2014

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

mitra gh
- karaj, iran

August 22, 2014

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

October 15, 2014

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

gregorita mae
- rosario cavite, philippines

April 13, 2016

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

mp mishra
- gandhidham, india

October 10, 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 interduce 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

December 12, 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

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