Fluoride removal in the presence of organophosphates: application to chemical warfare agent destruction

Abstract

New international policy and the inherent danger of chemical weapons storage has produced an unprecedented demand for the destruction of chemical warfare agent (CWA) stockpiles. In the face of bitter opposition to the use of incineration for disposal, policy makers have been forced to examine other, more environmentally sound alternatives. One such alternative is the use of a combined chemical and biological treatment system. Sarin (GB), one of the more prevalent nerve agents stockpiled by the U.S. and Russia, undergoes a hydrolysis reaction in the presence of water and sodium hydroxide to form isopropyhnethylphosphonic acid (IMPA) and sodium fluoride. IMPA can. be degraded biologically to form methylphosphonic acid (MPA) and eventually phosphate. The purpose of this study was to identify what currently available technology could separate fluoride from a waste stream containing these GB degradation products. Chemical precipitation, ion exchange, and adsorption were examined for their ability to remove fluoride from the matrix. While poor separation was achieved by chemical precipitation and ion exchange, activated alumina was able to effectively separate fluoride from MPA and IMPA. Activated alumina was shown to exhibit a strong affinity for alumina, even at high pH, and in the presence of IMPA and MPA. A design using multiple columns containing fluidized beds of alumina placed prior to biological treatment was chosen as a likely reactor configuration. By placing the fluoride removal system ahead of biological treatment, this design would protect microorganisms from fluoride toxicity. The use of a fluidized bed prevented the clogging often associated gravity beds, and maximized the fluoride capacity of the alumina.