Information on selenium, selenium waste disposal issues and related topics. Sponsored by Perma-Fix Environmental Services, Inc.,
General Scientific; Occurance
Selenium is a semimetallic element, symbol Se and atomic number 34. It exists in several powder and crystalline forms (a property called allotropy). It is found naturally in a few mineral ores, often in sulfide ores. It may also be unintentionally introduced into the environment by human activity, including burning of coal or oil, and in commercial wastes.
Selenium is commercially produced, primarily as a by-product of the refining of copper-sulfide ores. Selenium and its compounds have many uses, including in electronics, photo conductors, optics, glass, ceramics, plastics, paints, anti-dandruff shampoos, and in nutritional supplements for animals and humans.
Selenium is an essential nutrient for humans and animals, however, it can be toxic if
ingested over periods of time at amounts only 5-10 times higher than
those required for normal functioning. Some selenium compounds are
Treatment and Disposal Issues
Selenium exists in many oxidation states, making it difficult to develop one general
The Environmental Protection Agency has determined the "Best Demonstrated Available
Technology" for the pre- and final treatment of many listed and characteristic hazardous
wastes is chemical stabilization.
Treatment of Industrial Waste Water
A number of technologies have been developed or are under development for treatment of waste water contaminated with selenium (see below). Issues with industrial water include complexity of the waste stream (multiple contaminants) and large volume. Technologies developed for drinking water treatment typically are either technologically unable to handle complex waste and/or too expensive for large volumes.
Waste water treatments or potential treatments include reverse osmosis, emulsion liquid membranes, nanofiltration, precipitation, adsorbtion, reduction processes including bioreduction (see Twidwell et. al. below for a recent review of the literature and brief discussion of the technologies)
Perma-Fix Environmental Services, a commercial waste treatment, storage and disposal corporation, has developed a cost effective, efficient broad treatment solution. The two-step procedure separates, by precipitation, selenium from the waste water stream to the point the water can be disposed of by deep well injection (at Perma-Fix's Tulsa Facility). The remaining filter cake sludge is treated with the Perma-Fix Process so that it meets land ban restrictions to allow inexpensive disposal.
- Twidwell, L.G., J. McCloskey, P. Miranda, M. Gale, Technologies and Potential Technologies for Removing Selenium from Process and Mine Wastewaters, Proceedings Minor Elements 2000, SME, Salt Lake City, UT., Feb. 2000, pp 53-66. (At Department of Metallurgical and Materials Engineering
Montana Tech of The University of Montana).
- Emulsion Liquid Membrane Extraction (abstract)
- Research on Agricultural Drainage (1994, L. Berkeley National Lab research)
Treatment of Soils, Solids
Perma-Fix Environmental Services, a commercial waste treatment, storage and disposal corporation, has developed a proprietary, cost-effective process which is effective on a variety of selenium contaminated waste streams and exceeds current EPA standards. The Perma-Fix Process applied to soluble (TCLP) selenium chemically reduces it to an insoluble, non-toxic form. This method is operated at ambient temperature and atmospheric pressure. The waste container itself is used as the chemical reactor. The waste is slurried with water and the reagent thoroughly mixed. The conversion is confirmed in real time by conducting an endpoint test with a wet chemistry method.
Following conversion and analytical confirmation, the material is hydrolyzed (chemically dried) into a compliant form appropriate for safe disposal as a non-hazardous solid waste. Soluble selenium is regulated when present greater than 1 mg/L. Disposal requires treatment to below 5.7 mg/L.
Beath Selenium Database at the University of Wyoming. Articles.
Selenium related WWW sites (link list) at the University of Idaho.