Abstract
2,4,6-Trinitrotoluene (TNT) is a major groundwater contaminant at military bases and ordnance manufacturing and testing facilities. Remediation methods to date are costly and invasive, often to a prohibitive degree. Application of nanoscale zero-valent iron (NZVI) particles for contaminant removal offers a more cost-effective, less invasive method of treatment. NZVI particles were synthesized using sodium borohydride and iron (III) chloride. A mass of 5 g/L of NZVI was found to degrade 75 mg/L of TNT completely in under 30 min. Diaminonitrotoluenes accumulated in solution and only 60.7% of initial TNT was recovered as final products. Aminodinitrotoluene reaction rates were three times slower than TNT reaction rates. Reaction kinetics suggested a pseudo first-order relationship between NZVI and TNT, with an average rate of 0.216 L/min, but as the NZVI particles were increasingly oxidized, second-order kinetics became significant. Through a respiking experiment where NZVI was repeatedly exposed to fresh TNT, the treatment capacity of nanoscale NZVI was determined. Based on modeling of the respiking experiment, 4.04 mg of NZVI was required to degrade each mg of TNT. This was 2.7 times the stoichiometric requirement for metallic iron as a reductant of TNT to DANT. Excess iron was required because once nanoparticle surfaces were oxidized, interior iron was likely not available for reduction.
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