Ion Exchange is a process in which ions of a species are displaced from an insoluble exchange material (ion exchange resin) by ions of a different species in water. The removal of target ions is achieved through commercially available ion exchange resins that exchange target anions for chlorine (Cl-) or hydroxide ion (-OH), and target cations for sodium (Na+) or hydrogen protons (H+).
The ion exchange resins are small polymer beads designed for large polymer-water contact areas where ion exchange takes place. The resin is placed in packed columns where it is placed in contact with water until the ion exchange capacity is exhausted. To remove solids and restore the resin ion exchange capacity, the resin is replaced or backwashed with a prepared solution of salt, acid, or sodium hydroxide solution. The backwash solution is prepared based on the resin.
Ion exchange systems will generate a waste brine containing the ions removed from the backwashed resin, and may require further treatment. Brine is normally disposed into a sewer or brine line.
Ion exchange systems are demonstrated technology in the removal of many ions and have proven their effectiveness in residential, commercial, and industrial water applications for the removal of hardness, inorganics (nitrates, perchlorate) and heavy metals. Ion exchange system selection, design, and specification will depend on the water chemistry, flows, initial concentrations and target concentrations. Many resins have been permitted for their use in drinking water applications.
Experience and Target Contaminants
Selection of an ion exchange resin and design of require knowledge of the flows, target chemicals and water chemistry. Ion exchange has often been selected as the preferred water treatment alternative in the treatment of water impacted with metals such as hexavalent chromium and selenium and inorganics such as perchlorate.
Ion exchange systems are sold as pre-packaged systems by ion exchange suppliers. These systems are easily purchased, delivered, pre-assembled or assembled on-site, which makes them easy to implement. Equipment suppliers rent ion exchange systems for temporary projects such as dewatering during construction.
Ion exchange systems are demonstrated, cost-effective process solutions proven for wide variety of applications. The cost will vary based on capital costs, process flow, raw water chemistry, required treated water quality, resin selection, brine disposal options, and resin replacement or regeneration.
Our project experience with ion exchange systems includes:
- Removal of selenium from groundwater and discharge to storm drain
- Hexavalent chromium removal from drinking water
- Perchlorate removal from drinking water
- Nitrates removal from drinking water