| As a vital part of water resource, groundwater is an important resource formunicipal, industrial and agricultural water supply. Groundwater resources play animportant role in human’s manufacture and daily life, as well as the development ofnational economy. Groundwater contamination is a slow process that is hard to befound. In recent years, dense non-aqueous phase liquids (DNAPLs) entered thegroundwater and soil environment through accidental spills, improper disposalpractices or leaking from storage system. As a kind of chemical material,nitrobenzene has been considered as a significant groundwater contaminant due to itswide usages in national defense, pharmacy, dyeing and other industries. Nitrobenzeneis difficult to be biodegraded and poses harm to human health and environment, so itis listed as priority pollutant by American Environmental Protection Agency (EPA).Nitrobenzene presents at contaminated site as DNAPL sources and/or as dissolvedphase in a plume. Because its low solubility, the DNAPL source in aquifer presents aseparate water immiscible phase that slowly dissolves and acts as a constant and long-term (hundreds of years) groundwater contamination source.In situ reactive zone using nanoscale zero-valent iron (NZVI) slurry is a veryeffective technique for the remediation of organic solvents polluted soil andgroundwater. The nanoparticle water slurry can be injected to the contaminated sourceto remedy polluted groundwater directly, which poses a great advantage over thetraditional pump and treat technology or PRB applications. However, because of itshigh surface energy and intrinsic magnetic forces, bare NZVI is unstable and couldnot be effectively transported through water-situated porous media. Bare NZVIpresents low efficiency in reducing DNAPL source zone. Emulsified nanoscale zero-valent iron (EZVI) is desired as a modification of bare nano particle. EZVI iscomposed of food-grade surfactant, vegetable oil, water, and NZVI, it is an emulsionthat contain the NZVI particles in water surrounded by an oil-liquid membrane. Themodification of reactive iron particles by the oil film has shown some advantages overbare NZVI. Firstly, the surfactants and oil contained by EZVI are utilized to increaseits stability and improve its transport in water-saturated porous media by enhancingsteric and electrostatic repulsions which are attributed to prevent aggregation andattachment to sand grains. Additionally, location of iron particles within oil membrane may limit corrosion during delivery by protecting iron from groundwaterconstitutes, such as inorganic ions. Secondly, the exterior emulsified oil-liquidmembrane contains both hydrophobic and hydrophilic blocks. The hydrophobicproperties are similar to that of DNAPL, therefore, EZVI may be applied to promotenonpolar interaction by improving intimate contact between DNAPL and reactive ironparticles. Thirdly, some findings have demonstrated that emulsified oil containingfood-grade surfactant and vegetable oil may serve as long-term electron donors andpromote the anaerobic biodegradation of the organic contaminants in the subsurfaceenvironment.This paper intends to provide valuable insights to the application of nanoscalematerials in in-situ remediation. In this research, EZVI is produced and characterizedby XRD, BET, and TEM. The stability, reactivity and transportability of EZVI werediscussed.(1) In this research, EZVI is produced by coating an emulsified vegetable oilmembrane on the surface of Fe nanoparticles and characterized by XRD, BET, TEM.A stable and good dispersive EZVI suspension was synthesized. XRD and TEMresults suggest that the EZVI yielded a mean value of diameter100±50nm, and itsmain component was α-Fe0.The NZVI was uniformly surrounded by an oil-liquidmembrane, few aggregations were observed.(2) EZVI could provide significant removal of nitrobenzene through adsorption andreductive reaction. The Kinetics of nitrobenzene reduction by EZVI followed apseudo-first-order kinetics; the observed rate constant of nitrobenzene is0.0942min-1.The addition of EZVI may produce an increase in pH and decline in solutionoxidation-reduction potential, which is beneficial to stimulus anaerobic degradation insubsurface. The oil concentration used to modify NZVI has significant influence onthe performance of EZVI, and the oil concentration of1%and2%tended to bepreferred then that of0.4%and5%. The content of iron is crucial for the nitrobenzeneremoval, the rate of nitrobenzene degradation and aniline formation increased as theincrease of Fe: NB mole ratio. The initial pH has profound effect on the nitrobenzenereduction. The removal efficiency were64.82%,63.27%,66.63%,68.75%,71.38%atpH value of4,5.5,7,8.5,10, respectively. Lower pH is favorable to the nitrobenzenereduction by EZVI. (3) The modification of nanoscale zero-valent iron by oil emulsion improved thestability of iron suspension, no obvious sedimentation was observed in30min. Thestability decreased as the increase of iron concentration, while increased as theincreasing dose of surfactants.(4) The modification of nanoscale zero-valent iron by oil emulsion improved thetransportability of iron emulsion, compared with bare NZVI suspension, the transportdistance improved from4cm to11cm. The iron and oil phase got separated throughthe porous media, which is favorable to the in-situ application. |
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