Potable Water: Selenium can be selectively removed with ADSORBSIA™ arsenic removal media due to the chemical similarities of selenium and arsenic. ADSORBSIA has an excellent capacity for Se(IV) (selenite) while Se(VI) (selenate) is not removed. If you have a commercial selenium removal application, please Contact Us via the link on this page. Please include information about your particular selenium removal application.
Wastewater: If Se is oxidized, it is present as the anion selenate SeO4-2 that can be removed from solution with an anion exchange resin. There are three ion exchange options to consider; DOWEX™ M-43, DOWEX 21K XLT and DOWEX™ MARATHON™ A2 resins. The DOWEX M-43 is a weak base resin and will remove weak acids, like selenate from water. The influent should be weakly acidic, pH of 2-5. The resin will also remove other weak acids like carbonic acid. If the stream is not acidic, then a strong base resin like DOWEX 21K XLT resin will be required. Here the resin will remove all of the anions along with the Se. For streams that have a high organic content and are prone to surface fouling, DOWEX MARATHON MSA resin is recommended. For solutions with higher levels of sulfate of chloride, you may want to use the Type II anion exchanger DOWEX MARATHON A2.
Selenium also exists as selenium dioxide or the hydrated selenite; SeO3-2 or HSeO3-. While selenite is anionic, it is a weaker acid so it is more difficult to remove from solution. In some cases, removal may be improved by fully oxidizing the selenium.
Selective Selenium Removal has been described using a metal hydroxide loaded ion exchange resin. This approach is particularly valuable in high salt streams like brines. See reference below (1,2,3). Selenium can also be selectively removed with chelating resins loaded with oxyanions (4). Selective adsorption of Selenite has also been demonstrated on ADSORBSIA media.
NF membranes have also been described to remove selenium from ground water. In laboratory tests, 95+% of the selenium from a sample of water obtained from the San Joaquin Valley was removed with a nanofiltration membrane. The Se+6 (99%) was preferentially removed vs. the Se+4 (~40%). However, since the predominate selenium species is the Se+6, the majority of the selenium was removed. The proportion of water that can be decontaminated by nanofiltration will vary depending upon its chemical composition. However, 90+% is expected. Cost of removal is in the range of $1/1000 gallon or $325/acre foot. See reference below (5).
1. "Method of purification of salt solution for electrolysis", Oohara, C.; Matsuoka, T.; Kishi, T. and Okuno, T. of Chlorine Engineers Corp., Ltd. European Patent Application EP 0 987 221 A1 (1999).
2. US Patent 4,415,677 "Removal of sulfate ions from brine using composite of polymeric zirconium hydrous oxide in macroporous matrix" Lee; John M. ; Bauman; William C. Assignee: The Dow Chemical Company (1983).
3. US Patent 4,415,678 "Removal of sulfate ions from brine using amorphous polymeric zirconium oxide formed within a macroporous polymer matrix" Lee; John M. ; Bauman; William C. Assignee: The Dow Chemical Company (1983).
4. Removing selenium(IV) and arsenic(V) oxyanions with tailored chelating polymers. Ramana, Anuradha; Sengupta, Arup K.. ERM Inc., Exton, PA, USA. J. Environ. Eng. (N. Y.) (1992), 118(5), 755-75.
5. Removal of Selenium from Contaminated Agricultural Drainage Water by Nanofiltration Membranes, Yousif Kharaka, Gill Ambats, Theresa Presser, and Roy A. Davis, US Geological Survey, Applied Geochemistry, Vol 11, No. 6. Pp. 797-802.
|Selenium - Se
Selenium is below sulfur on the periodic chart so it forms many of the same compounds. Selenium is an interesting compound as it is classified as an essential nutrient so it appears in all kinds of health food supplements and yet there are severe limitations on the discharge of this compound. Selenium forms as many as five different oxidation states. Some are anions, some are neutral and some are cations.