Role of expandable clays in the environmental fate of trinitrotoluene contamination. Final report

A primary goal of the US military cleanup effort is to develop technologies that can expedite the remediation of explosive contaminants in soils. Nitroaromatic explosives are known to be strongly adsorbed by soils, with as much as 20 to 50 percent of radio-labeled explosives not extractable in controlled degradation studies. This suggests that adsorption of explosives and explosives degradation products onto soil components renders them unavailable to conventional extraction methods. The mechanism of sorption to soil components has been investigated in order to properly address the ultimate fate of explosives contamination. Trinitrotoluene undergoes reductive degradation in which nitro groups are animated to produce aminotoluene compounds. The final compound predicted by this reduction scheme is triaminotoluene. This reaction pathway results in intermediate degradation products of trinitrotoluene which act as weak bases. Protonation of these weak bases produces organic cations which are capable of sorption onto soil components. Sorption experiments were performed to determine the behavior of explosives and explosive by-products on pure clay minerals. X-ray diffraction studies measuring the interlamellar distance of expandable clays show an expansion as contaminants are bound to the clay, indicating displacement of interlayer cations. This intercalation of compounds of environmental interest within the interlamellar regions ofmore » expandable clays is an important geochemical event with implications toward a number of environmental disciplines including subsurface contaminant transport, risk assessment, contaminant bioavailability, site remediation, and natural attenuation.« less