Wednesday, August 17, 2011

Common Cation Ion Exchange Resin Foulants

We are often asked to help with an ion exchange system that no longer has the same run length as when it was new. Typically, this is the result of either reversible or non-reversible fouling of the cation and/or anion ion exchange resin. These are some of the common foulants:

Clear Water Iron (ferrous iron) can be removed through a softener. As long as iron stays in the ferrous form, regenerating a softener with a salt brine solution will remove the iron off the resin. When ferrous iron becomes oxidized into ferric iron (small solid iron particles), this type of iron will coat the surface of the resin, as well as, penetrate the internal matrix of the resin bead. Two common oxidizing agents, which can be present in water during the service cycle, are chlorine and oxygen that can cause the ferrous iron to form into ferric iron.

Aluminum can be found in water due to the carryover of using Alum or Aluminum Sulfate in water treatment to remove suspended solids and turbidity. Aluminum will coat the resin and penetrate inside the resin bead causing poor exchange sites and reduce capacity.

Barium is a metal that can be removed by softening resin. If Barium precipitates into Barium Sulfate where the Sulfate is greater than two ppm and the Barium is less than one ppm, this will foul the cation resin and reduce it’s capacity.

Oil fouling typically occurs from leaks in oil-lubricated pumps. This will coat the resin causing short service cycles and poor product water quality. Dirt particles and broken resin beds will stick to oil and grease which also causes channeling of the resin bed.

Hardness Salts (Calcium & Magnesium):
This type of fouling occurs from improper resin regeneration. In a demineralizer or deionizer using sulfuric acid regeneration, calcium sulfate can form when the sulfuric acid regenerant is at too high a concentration or at too low a flow rate. This will lead to a gradual build up of hardness ions on the surface of the resin beads and within their structure. Once this occurs, regenerating the resin becomes more difficult which causes shorter service runs and reduces the resin life.

How Do I Figure out what the problem is?
The best way is to take a representative resin sample and have it tested. Please note, this may not be cost effective on small softeners because the labor cost of taking the sample and the resin analyses cost may be more than simply replacing with new resin. If you decide to have your resin tested, please fill out our Resin Analysis Submittal Form so we can start to figure out what the problem is. After that Mike Polito will have an RMA # issued so the resin sample can be received at Res-Kem.

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