Encapsulation/Fixation (E/F) Mechanisms.

The objective of this project was to examine the chemical and/or physical bonds created in the process of encapsulating/fixing AAP-type sludges. Typical sludge compositions were selected for detailed study on review of sludges generated during wastewater treatment and related operations at 22 Army facilities. Candidate fixatives included polysilicates, amine-cured polyepoxides and polysulfides. A limited study was also conducted using ion-exchange resins of the non-ionic type for sludges containing TNT and rdx; and cationic exchangers with specific chemically reactive groups for sludges containing heavy metals. The measure of effectiveness of the AAP sludge-fixative combination was EPA's EP Toxicity Test. Instrumentation characterization methods included optical microscopy, infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray analysis, and X-ray diffraction. Polysilicates were found to fix heavy metals as a consequence of the highly alkaline-buffered media they provide. Nitrocellulose was observed to react with epoxy ingredients with the possible removal of nitrato groups. Studies with polysulfides and ion-exchange resins were encouraging, resulting in chemically fixed sludges of high contaminant density and resistance to leaching.