Reactivity of Aluminum Lactate-Modified Nanoscale Iron Particles with Pentachlorophenol in Soils

Due to the hindered transport of nanoscale iron particles (NIP) in the subsurface caused by the agglomeration and adsorption of NIP during transport, the NIP surface has to be modified to improve the transport of NIP in the subsurface. This study assessed the effectiveness of surface-modified NIP for in situ degradation of contaminants using aluminum lactate as the modifying agent, where aluminum lactate had been earlier shown to be an effective dispersant for enhanced transport of modified NIP in the subsurface. The reactivity of bare-NIP and lactate-modified NIP (LM-NIP) was investigated using pentachlorophenol (PCP) as a representative chlorinated hydrophobic organic contaminant in kaolin and field sand as low permeability clayey soil and high permeability soil, respectively. Kaolin and field sand were spiked at 100 mg/kg PCP and at 89 mg/kg PCP, respectively. NIP dosages of 4, 10, 20, 50, 75, and 100 g/L were applied for a reaction period of 24 h. For the bare-NIP dosage of 100 g/L, PCP degradation of 98% and 99% was obtained in 24 h for field sand and kaolin, respectively. The effect of reaction time on reactivity of bare-NIP and LM-NIP was evaluated using a lower NIP dosage of 4 g/L for 1, 2, 4, 7, and 14 days. After 14 days, greater PCP degradation occurred in bare-NIP systems than in LM-NIP systems, where 95% and 99% degradation was obtained for field sand and kaolin with bare-NIP, respectively, whereas 90% and 91% degradation was obtained for field sand and kaolin with LM-NIP, respectively. Differences in PCP degradation between bare-NIP and LM-NIP diminished with time more rapidly for field sand than for kaolin. For both field sand and kaolin, nearly complete dechlorination of PCP to phenol occurred with bare-NIP with a more rapid dechlorination in field sand than in kaolin.