Transport Of Vegetable Oil Modified Nano-iron And Influence Factors On Nitrobenzene Reduction

Nitrobenzene (NB) is an important chemical basic material formanufacture of aniline and aniline derivatives, rubber, pesticides, dyes, drugsand other fields. Once released into the subsurface environment, NB willdistribute between soil and water, rendering NB a long term threat to theenvironment and human health.Nanoscale zero-valent iron (NZVI) present a new promisingenvironmental remediation technology that could provide cost-effectivesolutions for remediating groundwater contaminated. Nanoscale iron has agreat number of reactive sites and can be directly injected in contaminantsource areas due to its small particle size. However, these nanoscale particleschange over time when exposure to natural environment in groundwater,decreasing or entirely losing its reactivity. In addition evidence suggests thataggregation and deposition of NZVI limit the delivery of iron in aquifer.Vegetable oil modified nano-iron (VOMNI) is made from food-gradesurfactants, vegetable oil and water, which form emulsion droplets that containthe NZVI particles in water surrounded by an oil-liquid membrane. Theoil-liquid membrane enhances colloidal stability by excluding ionic and polarsolutes from entering the reaction aqueous core. Nano-iron surface coated filmcan effectively enhance the antioxidant capacity and dispersion properties ofnanoscale iron. VOMNI not only has good removal ability to the dissolvedphase of NB, but also its emulsion can increase the contact between theinsoluble NB and the NZVI within the droplet.In this paper, the perspective of using VOMNI in in-situ remediation isconsidered. The kinetics of NB reduction with VOMNI and effects ofgroundwater geochemical constituents(pH、Ca2+、Fe2+、Cl-、SO42-)on removalof organic pollutants have been investigated. Moreover, the transport mechanism and characteristics of VOMNI in porous media throughone-dimensional simulation experiments were analyzed. The research resultsare as follows:(1) The kinetics of NB reduction by VOMNI follows a pseudo-first-orderkinetics; the observed rate constant of NB reduction, kobs, is0.0783min-1. TheNZVI has a higher reactivity in NB reduction.(2)The geochemical constituents of groundwater have significant effect onthe VOMNI reactivity and the NB reduction. The lower pH can induce asignificant increase of the reduction of NB. Chloride and sulfate ions had aslight positive effect on the NB reduction and the formation of AN. The ferrousion can promote electron transfer leading to a promoted on the degradation ofNB. The calcium has inhibitory effect on the NB reduction.(3)The modification of nanoscale zero-valent iron by emulsified oilimproved the transportability of iron, the migration distance of VOMNI was2~3times compared with NZVI, The excess of emulsified oil in VOMNIsuspension would transport out first with the groundwater, forming tworeaction zones.(4)Larger size of the aquifer medium was good for the transport ofVOMNI, the migration distance in coarse sand was about1.9times than in thefine sand. when the injection speed of VOMNI was3cm/min, the slurryconcentration was2g/L, the migration has a maximum value, the geochemicalconstituents of groundwater have little effect on the VOMNI transport ability.