While many of us have heard of ion exchange (IX) resins, few of us have a grasp on how the technology actually works. Whether you’re weighing potential treatment strategies, looking for ways to get the most out of your existing IX resins, or simply curious about IX chemistry, you may be asking “What is ion exchange resin and how does it work?”
No matter your goals, this article will help you to make better decisions on the right water treatment strategies for your facility by helping you to better understand IX resin technology, and how it serves a variety of water treatment and separation needs.
Ion exchange is a reversible chemical reaction where dissolved ions are removed from solution and replaced with other ions of the same or similar electrical charge. Not a chemical reactant in and of itself, IX resin is instead a physical medium that facilitates ion exchange reactions. The resin itself is composed of organic polymers that form a network of hydrocarbons. Throughout the polymer matrix are ion exchange sites, where so-called “functional groups” of either positively-charged ions (cations) or negatively-charged ions (anions) are affixed to the polymer network. These functional groups readily attract ions of an opposing charge.
The geometric shape, size, and structure of IX resins can vary from one type to the next. Most IX exchange systems employ a resin bed consisting of tiny, porous microbeads, though some systems, such as those used for electrodialysis, use a sheet-like mesh resin. IX resin beads are usually small and spherical, with a radius measuring just 0.25 to 1.25 millimeters in size. Depending upon the application and system design, the resin beads may have a uniform particle size or a Gaussian size distribution. Most applications use gel resin beads, which have a translucent appearance, and offer high capacity and chemical efficiency. Macroporous resins, which are recognizable due to their opaque white or yellow appearance, are typically reserved for demanding conditions, since they have comparatively greater stability and chemical resistance.