Ion exchange is a remediation process that removes dissolved metals and other inorganic chemicals (e.g, perchlorate) from liquids. An ion is an atom or group of atoms that has lost an electron (making it positively charged) or gained an electron (making it negatively charged). Liquids are passed over a resin bed where ions (i.e., cations and anions) in the resins and in contaminated materials are exchanged. The resins attract the metallic ions. After the resin capacity has been exhausted, some can be regenerated for re-use, while others are meant for single use.
Limitations and Concerns
Oil and grease in the groundwater may clog the exchange resin.
The acidity or alkalinity of the incoming water may limit ion exchange capability. This can usually be controlled.
Oxidants in groundwater may damage the ion exchange resin.
Wastewater is generated during the regeneration step and requires additional treatment and disposal.
The process does not destroy the contaminants; it transfers them to a different medium which must be treated or disposed of.
If the system is designed as a single-use system, resin must either be disposed in a landfill or incinerated.
Stakeholder concerns include location of the treatment facility, facility size, potential odors, noise generation associated with the treatment facility, and sometimes the choice of a single-use resin or a regenerable resin.
Ion exchange can remove dissolved metals (chromium) and radionuclides from contaminated liquids. It can also be used to remove non-metallic compounds such as perchlorate, nitrate, and ammonia.
Technology Development Status
This technology has long been used in industry and is commercially available. Specific resins must be designed for specific contaminants.
See http://www.itrcweb.org/Documents/PERC-2.pdf (Section 5.1) for a description of Ion Exchange for removal of perchlorate from water. This section includes a list of ion exchange projects involving perchlorate.
See http://www.osti.gov/bridge/product.biblio.jsp?query_id=3&page=1&osti_id=770689 for a uranium remediation project at Fernald. The project was successful in that an efficient method for regenerating resins was developed that was comparable to using new resins.