Ion exchange resin An ion-exchange resin is an insoluble matrix (or support structure), normally in the form of small (1-2mm diameter) beads, fabricated from an organic polymer substrate on the surface of which are sites with easily trapped and released ions. There are multiple different types of ion-exchange resin which are fabricated to selectively prefer one or several different types of ions. They are used extensively for water purification and water softening. They were developed as a more flexible alternative to the use of natural or artificial zeolites There are four main types: strong acid strong base weak acid weak base There are also specialised types: chelating resin Uses Water Softening In this application ion-exchange resins are used to replace the magnesium and calcium ions found in hard water with sodium ions. When the resin is fresh, it contains sodium ions at its active sites. When in contact with a solution containing magnesium and calcium ions (but a low concentration of sodium ions), the magnesium and calcium ions preferentially migrate out of solution to the active sites on the resin, being replaced in solution by sodium ions. This process reaches equilibrium with a much lower concentration of magnesium and sodium ions in solution than was started with. The resin can be recharged by washing it with a solution containing no magnesium and calcium ions, but a high concenration of sodium ions (e.g. it has large amounts of common salt dissolved in it). The calcium and magnesium ions migrate off the resin, being replaced by sodium ions from the solution until a new equilibrium is reached. This is the method of operation used in dishwashers that require the use of 'dishwasher salt'. The salt is used to recharge an ion-exchange resin used to soften the water so that limescale deposits are not left on the cooking and eating utensils being washed. Water Purification In this application, ion exchange resins are used to remove poisonous (e.g. copper) and heavy metal (e.g. lead) ions from solution, replacing them with more innocuous ions, such as sodium and potassium. Note that this is why it is not recommended to prepare artificial milk (infant formula) with softened water, as the increased levels of sodium and potassium in the diet can be deleterious to nursing infants. Ion exchange resins do not remove chlorine and organic contaminants from water - this is usually done by using an activated charcoal filter mixed in with the resin. Domestic water purification is not usually recharged - the resin is discarded when it should no longer be used. Sources http://www.remco.com/ix.htm http://www.rohmhaas.com/ionexchange/IP/faq_general.htm FAVORITE ARTICLES: History of the World    History of the United States    History of Europe    Ancient History    History    Military History    World War I    Bombing of Dresden    California    US Constitution    Frank Sinatra    Boston    Marbury v. Madison This article is licensed under the GNU Free Documentation License at http://www.gnu.org/copyleft/fdl.html You may copy and modify it as long as the entire work (including additions) remains under this license. You must provide a link to http://www.gnu.org/copyleft/fdl.html To view or edit this article at Wikipedia go to http://www.wikipedia.org/wiki/Ion_exchange_resin