Soils and sludges contaminated with energetic materials present handling problems during recovery and reuse operations. USAEC has established a guideline that soils containing greater than 10% energetic materials by weight should be considered explosive during handling and transportation. As a general rule, soils and sludges containing less than 10% energetic materials by weight pass USAEC's nonreactivity tests. Reuse/recycle options are more feasible for contaminated soils and sludges meeting the nonreactivity criteria because they can be removed, transported, and handled using conventional equipment, which could provide a substantial cost savings.
Solvent Extraction: Solvent extraction is a technology that the Army originally determined to be infeasible for treating explosives-contaminated soils. The technology, however, might have potential for treating these soils if a few lingering technical issues can be resolved. In 1982, the Army conducted laboratory-scale solvent extraction on explosives-contaminated lagoon samples from a number of sites. Each sample was washed with a solution of 90% acetone and 10% water. This process achieved greater than 99% contaminant removals.
In 1985, the Army conducted a pilot-scale engineering analysis to determine the feasibility of full-scale solvent extraction. This analysis indicated that, for solvent extraction to be economically feasible, the number of required washes would have to be reduced, and acetone would have to be recovered and reused. Currently, the only available technology for recovering acetone is distillation, which exposes acetone to heat and pressure. Exposing a solvent that has been used to extract explosive contaminants to heat and pressure raises serious safety considerations. In fact, the distillation column used to recover acetone often is referred to as an 'acetone rocket.' Nevertheless, the Army believes that full-scale solvent extraction would be feasible if a safe, efficient, alternative recovery method were developed.
Soil Washing: A soil washing procedure, termed the Lurgi Process, currently is being developed in Stadtalendorf, Germany. Although no data have been published on the effectiveness of this process, initial reports suggest that the process can reduce levels of explosive contamination in soils to low ppm levels. As with all soil washing technologies, the Lurgi Process produces secondary wastes, such as washwater and concentrated explosives.
In the Lurgi Process, contaminated soils are excavated and processed in an attrition reactor, which detaches the explosive material from the soil particles. The remaining material undergoes a second process, which separates clean from contaminated particles. Clean particles are dewatered, separated into heavy and light materials, and returned to the site.
Solar Detoxification: Experimental work conducted by the DOE and elsewhere has shown that photocatalytic oxidation can be used to successfully destroy a wide range of organic compounds in water. The process does not require the addition of other reagents such as ozone or hydrogen peroxide and can operate under sunlight or lamps, so it has the potential to be of lower cost than others that have been studied. The relative costs of photons from lamps and sunlight have been compared, and the solar option is competitive at sites throughout the U.S.
The photocatalytic process uses a semiconductor catalyst such as titanium dioxide (TiO2) in conjunction with near UV light to generate strongly oxidizing and reducing species. Use of the process to destroy TNT in water has been shown with mixed results. While some research has produced evidence for effective removal of TNT, others have found only partial success. The difference may lie in the susceptibility of TNT and related compounds to both oxidation and reduction. Preliminary experimental results support this idea. Reductive chemical processes have received very little attention so this opens a new pathway for solving the pink water problem.