Remediation of Explosive-Contaminated Soils: Alkaline Hydrolysis and Subcritical Water Degradation

Abstract

Alkaline hydrolysis and subcritical water degradation were investigated as ex-situ remediation processes to treat explosive-contaminated soils from military training sites in South Korea. The addition of NaOH solution to the contaminated soils resulted in rapid degradation of the explosives. The degradation of explosives via alkaline hydrolysis was greatly enhanced at pH ≥12. Estimated pseudo-first-order rate constants for the alkaline hydrolysis of 2,4-dinitrotoluene (DNT), 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in contaminated soil at pH 13 were (9.6 ± 0.1)×10−2, (2.2 ± 0.1)×10−1, and (1.7 ± 0.2)×10−2 min−1, respectively. In the case of subcritical water degradation, the three explosives were completely removed at 200–300°C due to oxidation at high temperatures and pressures. The degradation rate increased as temperature increased. The pseudo-first-order rate constants for DNT, TNT, and RDX at 300°C were (9.4 ± 0.8)×10−2, (22.8 ± 0.3)×10−2, and (16.4 ± 1.0)×10−2, respectively. When the soil-to-water ratio was more than 1:5, the extent of alkaline hydrolysis and subcritical water degradation was significantly inhibited.