Ion exchange (IX) systems are used across a variety of industries for water softening, purification, and separation purposes. While the chemistry of individual ion exchange reactions vary from one application to the next, IX is a treatment process where dissolved ions are replaced by other, more desirable, ions of a similar electrical charge.
If you’re wondering whether IX is right for your facility, you might be asking “What is an ion exchange system and how does it work?”
The following article offers a simple explanation of how IX technology works, what you can expect from an IX system, and how IX is used in common industrial applications.
What is an ion exchange system?
IX systems separate ionic contaminants from solution through a physical-chemical process where undesirable ions are replaced by other ions of the same electrical charge. This reaction occurs in an IX column or vessel where a process or waste stream is passed through a specialized resin that facilitates the exchange of ions. A common example is a water softening IX system, where the goal is to remove scale-forming calcium or magnesium ions from solution. When the solution is passed through an IX resin comprised of concentrated sodium ions, the calcium and magnesium ions are effectively captured from solution and held by the resin, while the sodium ions are released from the resin into the effluent stream.
What’s included in a basic ion exchange system?
A well-designed IX system conforms to the conditions of a specific application in both physical design specifications and in the chosen IX resin material. Common components of a basic IX vessel include:
- IX resin
- Inlet distribution system
- Regenerant distribution system
- Retention elements
- PLC, control valves and piping
IX resins are the most critical factor in IX system design. The substances present in the feed stream, as well as other process conditions, will determine the geometric shape, size, and material used in the IX resin.
How does ion exchange work?
By definition, ions are charged atoms or molecules. When an ionic substance is dissolved in water, its molecules dissociate into cations (positively-charged particles) and anions (negatively-charged particles). Taking advantage of this characteristic, IX selectively replaces ionic substances based on their electrical charges. This is accomplished by passing an ionic solution through an IX resin that serves as a matrix where the ion exchange reaction is allowed to take place.
Most commonly, IX resins take the form of tiny, porous microbeads, though they are sometimes available as a sheet-like membrane. IX resins are fashioned from organic polymers, such as polystyrene, which form a network of hydrocarbons that electrostatically bind a large number of ionizable groups. As the process or waste stream flows through the IX resin, the loosely-held ions on the surface of the resin are replaced by ions with a higher affinity for the resin material.
Over time, the resin becomes saturated with the contaminant ions, and it must be regenerated or recharged. This is accomplished by flushing the resin with a regenerant solution. Typically consisting of a concentrated salt, acid, or caustic solution, the regenerant reverses the IX reaction by replenishing the cations or anions on the resin surface, and releasing the contaminant ions into the waste water.
What contaminants do ion exchange systems remove?
The most common application of IX is sodium zeolite softening, though other popular applications include high-purity water production, dealkalization, and metals removal. IX can be an extremely effective strategy for removal of dissolved contaminants, though IX resins must be carefully chosen based on the substances present in the feed stream, as listed below.
Cation exchangers can be classified as either strong acid cation (SAC) resins or weak acid cation (WAC) resins, both of which are extensively used for demineralization. SAC resins are also commonly used for softening, while WAC resins are used for dealkalization applications. Contaminants removed by cation resins typically include:
- Calcium (Ca2+)
- Chromium (Cr3+ and Cr6+)
- Iron (Fe3+)
- Magnesium (Mg2+)
- Manganese (Mn2+)
- Radium (Ra2+)
- Sodium (Na+)
- Strontium (Sr2+)
Anion exchangers can be classified as either strong base anion (SBA) resins or weak base anion (WBA) resins. SBA resins are frequently used for demineralization, while WBA resins are often used for acid absorption. Contaminants removed by anion resins typically include:
- Carbonates (CO3)
- Chlorides (Cl–)
- Cyanide (CN–)
- Nitrates (NO3)
- Perchlorate (ClO4-)
- Perfluorooctane sulfonate anion (PFOS)
- Perfluorooctanoic acid (PFOA)
- Silica (SiO2)
- Sulfates (SO4)
While specialty IX resins are highly effective for specific industrial applications, their greater specificity generally means greater expense and narrower adoption than conventional IX resins. Chelating resins, for example, are used extensively for concentration and removal of metals in dilute solutions, such as Cobalt (Co2+) and Mercury (Hg and Hg2+). Similarly, magnetic ion exchange (MIEX) resins are often deployed for removal of natural organic matter from feed water.
How SAMCO can help?
SAMCO has over 40 years’ experience custom-designing and manufacturing IX systems for a range of industries and solutions, so please feel free to reach out to us with your questions. For more information or to get in touch, contact us here to set up a consultation with an engineer or request a quote. We can walk you through the steps for developing the proper solution and realistic cost for your IX treatment system needs.