Information on selenium, selenium waste disposal issues and related topics. Sponsored by Perma-Fix Environmental Services, Inc., www.perma-fix.com.
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.
ATSDR (Agency for Toxic Substances and Disease Registry) Public Health Statment for Selenium. Good general overview of properties, sources (natural and man made) and commercial uses, as well as toxicology issues.
USGS Minerals Information, overview as a commodity. This USGS Minerals Information Site also provides statistics and information on the supply, demand, and flow of minerals and other materials.
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 carcinogenic.
Toxicity/Carcinogenicity of some selenium compounds: National Toxicology Program Web Site - click on "Search" and then enter "selenium".
Selenium exists in many oxidation states, making it difficult to develop one general treatment method.
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.
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.
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).
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.