The Effect of Acid Neutralization on Analytical Results Produced from SW846 Method 8330 after the Alkaline Hydrolysis of Explosives in Soil

Abstract

Abstract : Alkaline hydrolysis has been used in several laboratory studies and field demonstrations for the treatment of energetic compounds (particularly, 2,4,6-trinitrotoluene (TNT), dinitrotoluene (DNT), and hexahydro-1,3,5- trinitro-1,3,5-triazine (RDX)) in soil. The application of alkaline hydrolysis for treatment of soil involves mixing a caustic source material with soil. Two caustic materials have been explored, calcitic hydrated lime [Ca(OH)2, HL] and sodium hydroxide (NaOH). Evaluation of explosives removal is routinely performed using SW-846 Method 8330. This method was developed before the advent of alkaline hydrolysis treatment, and recent studies have indicated that some errors can occur when this method is applied to alkaline hydrolysis samples. This report documents the results of a field study conducted to demonstrate the issue of false degradation in field-collected samples. The field study was followed by two laboratory studies: the first to confirm false degradation as a phenomenon and the second to develop an appropriate acid neutralization method. Results proved that false degradation can occur with alkaline hydrolysis (AH) samples, particularly if residual caustic material and moisture are present in the sample. Treatment systems using HL are more prone to extraction errors than systems using NaOH, although neutralization improves the accuracy of both treatment approaches. ERDC-EL has developed a neutralization method that can be used for alkaline hydrolysis approaches using up to 10% caustic addition (most systems are less than 5%) and a combination of H3PO4 and NaH2PO4. For remedial actions using alkaline hydrolysis, the scope of work for the action should include neutralization of all post- treatment samples, with appropriate control samples prepared in order to ensure that neutralization is achieved.