Transport and Reactivity of Lactate-Modified Nanoscale Iron Particles in PCP-Contaminated Soils

Remediation of sites contaminated by toxic chlorinated organic compounds by using nanoscale iron particles (NIP) has received great attention owing to their high reactivity resulting from small size and large reactive surface area. However, adequate delivery of NIP into the contaminated zones for in situ remediation applications is difficult because of NIP agglomeration and sedimentation. Different surface modifications of NIP are suggested to enhance the transport of NIP in soils. This study investigated the transport and remediation efficiency of bare NIP and lactate-modified NIP (LMNIP) in field sand contaminated with pentachlorophenol (PCP). Soil column experiments were conducted to investigate the reactivity and transport of NIP and LMNIP at different concentrations (1 and $4\mathrm{g}/\mathrm{L}$ ) under two different constant hydraulic gradients, and the consequent degradation of PCP in the soil. Bare NIP was transported only to limited distances and its distribution through the soil was nonuniform; however, LMNIP was transported uniformly throughout the soil column. Surface modification with aluminum lactate retarded agglomeration and sedimentation of NIP, but the reactivity of NIP decreased. Permeability of the soil was not impacted at low concentrations of NIP; however, at higher concentrations, NIP appeared to clog the pores, reducing soil permeability. LMNIP did not clog the pores even at higher concentration and maintained higher flow, indicating no impact on the permeability. The degradation of PCP was 53.2 and 54.8% with bare NIP at concentrations of 1 and $4\mathrm{g}/\mathrm{L}$ , respectively, whereas the degradation of PCP was 61 and 51.6% with LMNIP at concentrations of 1 and $4\mathrm{g}/\mathrm{L}$ , respectively. The removal of PCP from the soil on the basis of effluent analysis ranged from 6 to 14%. The low degradation of PCP may be attributed to varying reactivity depending on the dissociation and desorption of PCP from soil as a function of soil pH changes, as NIP is transported through the soil. Surface coating with lactate in LMNIP also may have hindered the direct contact of PCP with NIP during the initial stages of transport, but the reactivity of LMNIP increases to the same level as bare NIP at later times.