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TNT sorption and fate in munitions-contaminated soil: Implications for abiotic remediation
Abstract
Explosives-contaminated soil and water is a serious problem and remediation is required to insure public health and safety. Long-term TNT sorption, availability, and fate in soil were characterized and the potential use of zero-valent iron (Fe$\sp0$) to remediate munitions-contaminated soil and water was determined. TNT sorption on Sharpsburg soil was concentration-dependent and best described by the Freundlich model. Prolonged equilibration with soil revealed a gradual increase in TNT sorption and bound residue formation. After 168 d, 93% of the added TNT (70 mg L$\sp{-1}$) was adsorbed by uncontaminated surface soil and 79% was adsorbed on subsurface soil. In the presence of crystalline TNT, sorption in surface soil decreased to 79%. Readily and potentially available fractions decreased rapidly with equilibration time and about 40% of the sorbed TNT was irreversibly bound after 7 d. TNT adsorption-desorption exhibited biphasic kinetics. Desorption was slower than adsorption and exhibited hysteresis. A negative free energy change ($\Delta G\sp\circ$) indicated spontaneous adsorption. Enthalpy changes, $\Delta H\sp\circ$ and $\Delta H\sb{i}$, for TNT adsorption were negative and their magnitude ($\Delta H\sp\circ$ = -8.34 to -16.57 kJ mol$\sp{-1}$; $\Delta H\sb{i}$ = -9.16 to -13.87 kJ mol$\sp{-1}$) indicated that adsorption was primarily due to weak dispersion (van der Waals) and electrostatic attractions (hydrogen bonding). As little as 1% Fe$\sp0$ (w/v) removed 70 mg TNT L$\sp{-1}$ within 8 h and 32 mg RDX L$\sp{-1}$ solution within 72 h. Treating highly contaminated soil slurries with 10% Fe$\sp0$ reduced CH$\sb3$CN-extractable munitions below USEPA remediation goals of 17.2 mg TNT and 5.8 mg RDX kg$\sp{-1}$ soil from the former Nebraska Ordnance Plant. Sequential treatment of TNT (70 mg L$\sp{-1}$) solution with 5% Fe$\sp0$ and 1% H$\sb2$O$\sb2$ (added after 1 h) resulted in 48% mineralization within 8 h; 52% of the RDX (32 mg L$\sp{-1}$) was mineralized when H$\sb2$O$\sb2$ was added after 4 h. Fe$\sp0$-treated TNT was also more biodegradable. Results indicate that TNT-contaminated soils can be remediated by Fe$\sp0$ which promotes detoxification through enhanced bound residue formation.
Subject Area
Environmental science|Agricultural chemicals
Recommended Citation
Hundal, Lakhwinder S, "TNT sorption and fate in munitions-contaminated soil: Implications for abiotic remediation" (1997). ETD collection for University of Nebraska-Lincoln. AAI9725124.
https://digitalcommons.unl.edu/dissertations/AAI9725124