Separation of Selenium from Liquid Media

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Se

Potable Water

Selenium can be selectively removed with ADSORBSIA™ As600 Arsenic Removal Media due to the chemical similarities of selenium and arsenic. ADSORBSIA As600 has an excellent capacity for Se4+ (selenite) while Se6+(selenate) is not removed.

This resin may be subject to drinking water application restrictions in some countries. Please check the application status before use and sale. For more information see our regulatory information.

Nanofiltration (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 Se6+ was preferentially removed (99%) vs. the Se4+ (~40%). However, since the predominant selenium species is the Se6+, 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 below1.

Wastewater

If selenium is oxidized, it is present as the anion selenate (SeO42-) that can be removed from solution with an anion exchange resin.

AMBERLYST™ A21 Weak Base Anion Resin will remove weak acids, like selenate from water. The influent should be weakly acidic, pH of 2-5. This weak base anion 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 or chloride, you may want to use the Type II anion exchanger, DOWEX MARATHON A2 Resin.

Selenium also exists as selenium dioxide or the hydrated selenite; SeO32- 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

Selective selenium removal has been described using a metal hydroxide loaded ion exchange resin. This approach is particularly valuable in high salt streams like brines2 3 4

Selenium can also be selectively removed with chelating resins loaded with oxyanions5.

Selective adsorption of selenite (Se4+) has also been demonstrated on ADSORBSIA™ As600 Arsenic Removal Media.

1 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.

2 "Method of purification of salt solution for electrolysis" by Oohara, C.; Matsuoka, T.; Kishi, T., and Okuno, T. of Chlorine Engineers Corp., Ltd. European Patent Application EP 0 987 221 A1 (1999).

3 US Patent 4,415,677 "Removal of sulfate ions from brine using composite of polymeric zirconium hydrous oxide in macroporous matrix" by Lee, John M.; Bauman, William C. Assignee: The Dow Chemical Company (1983).

4 US Patent 4,415,678 "Removal of sulfate ions from brine using amorphous polymeric zirconium oxide formed within a macroporous polymer matrix" by Lee, John M.; Bauman, William C. Assignee: The Dow Chemical Company (1983).

5 “Removing selenium(IV) and arsenic(V) oxyanions with tailored chelating polymers” by Ramana, Anuradha; Sengupta, Arup K. ERM Inc., Exton, PA, USA. J. Environ. Eng. (N.Y.) (1992), 118(5), 755-75.

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.