Engineering Considerations for Hydroxide Treatment of Training Ranges

The use of hydrated lime has the potential to be an effective in situ technology for the destruction and containment of explosives contamination. This was proven with the results from the SERDP project CU-1230, where it was shown to rapidly degrade RDX and TNT. However, prior to field deployment of this technology additional experimental work was required to address concerns regarding the mechanism of the alkaline hydrolysis reaction, the character of the final products of the reaction, the potential for biodegradation of the reaction products, and the amount of lime required for alkaline hydrolysis in different soils. The results can be summarized as follows. First, spectroscopic studies of the TNT alkaline hydrolysis reaction identified two well-resolved and spectrally distinct reaction intermediates. A single radical species was formed during the TNT–hydroxide reaction that correlated with the second reaction intermediate. Second, TNT and RDX degraded rapidly through alkaline hydrolysis at pH 12.5. The end products of the reaction were low water-soluble molecular weight compounds that included nitrate and formate. No polymer formation was observed under these reaction conditions. Third, anaerobic and aerobic incubation of neutralized hydrolysis reaction mixtures with range soil showed that there is a high potential for biodegradation. This was evidenced by mineralization of reaction end products (production of [14C]-labeled carbon dioxide) and a decrease in nitrite and nitrate concentrations. Fourth, a simple method to predict the lime required by different soils under different environmental and contamination conditions was developed based on current ASTM methods for raising soil pH. A guidance document was prepared to provide site managers a means to easily and inexpensively determine the lime dosage required to raise pH to levels required for munitions and metals remediation. The results presented in this report indicate that a field demonstration of the alkaline hydrolysis technology is feasible. Data indicated alkaline hydrolysis followed a first order reaction mechanism that did not create side-chain reactions that could potentially form toxic by-products. This process efficiently degraded both nitroaromatic and nitramine explosives such as TNT and RDX to small molecules that were then used by inherent soil bacteria as carbon and nitrogen sources, indicating the reaction products were not harmful to soil microbes. In order to facilitate technology transfer, a guidance document concerning lime dosage was included in the report. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.