Potable Water

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.¹

Wastewater

If selenium is oxidized, it is present as the anion selenate (SeO₄^2-) 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 AmberSep™ 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, AmberLite™ HPR9200 Cl Resin is recommended. For solutions with higher levels of sulfate or chloride, you may want to use the Type II anion exchanger, AmberLite™ HPR4100 Cl Resin.

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

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.^2,3,4

Selenium can also be selectively removed with chelating resins loaded with oxyanions.⁵

References

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.