| In recent years,nanoscale zero valent iron(nZVI)attracts more and more attentions in contaminated environment remediation field.Nanoscale zero valent iron(nZVI)has numerous advantages including strong reducibility,absorbability and great reactivity,which contributed to the appliances of reducing refractory organic pollutants such as nitrobenzene,halogenated hydrocarbons and polychlorinated biphenyls.Due to the gravity and channel effects,it is difficult for the traditional nZVI to cover the entire contaminated area,which affects soil remediation.With the characteristics of low density,good fluidity and strong carrying capacity,colloidal gas aphrons(CGAs)could be a better underground carrier to improve the repairing effect instead of traditional carriers.In this research,we studied a continuous generator to produce CGAs continuously and evaluated its performance.And then we analyzed the influenced factors of CGAs stablization and the ability of CGAs to carry nZVI.Through the simulated column and dimensional experiments,CGAs and CGAs-nZVI transport pattern sand the variable principle of pressure in the soil system have been defined.Finally,we comprehensively evaluated the remediation efficiency of CGAs-nZVI for nitrobenzene contaminated soil.The mainly conclusions of this study are as follows:(1)Study on CGAs stability and capacity of nZVI-carryingThis study designed a continuously generating device for CGAs,which effectively solved the problem of temperature rising caused by continuous high-speed stirring process and ensured the stable output of CGAs and CGAs-nZVI.CGAs had a good capacity for carrying nZVI and the existence of nZVI did not influence the stability of foam.(2)CGAs migration characteristics and the change of pressure in the systemWith the increasing of particle size and water content of the medium,the pressure in the system was decreased.Besides,the results of the CGAs injection into soil from a single point on one side of the simulated tank indicated that the migration traces in the medium is nearly semicircular and CGAs distributed uniformly in the coverage area,overcoming the influence of gravity to its distribution in the medium.With the increasing of medium grain size,the CGAs sweep efficiency increased first and then decreased.The increase of water content in the medium also stimulated the increase of the sweep efficiency.(3)Temporal and spatial variation of transport and distribution of CGAs-nZVI in soilCGAs effectively enhanced the migration of nZVI in the medium and the ability of CGAs to transport nZVI is relatively weakly affected by the particle size,when the particle size is bigger than 1.0 mm.With the increasing of injection rate,the ability of CGAs for transporting nZVI has also been enhanced.CGAs-nZVI could overcome the influence of gravity to a large extent,so that nZVI presented a relatively regular semicircular distribution,but the distribution of nZVI is still affected by gravity which content was higher in the bottom of the soil than the top layer.(4)Study on the remediation effect of CGAs-nZVI on nitrobenzene contaminated soilCGAs-nZVI had a good removal effect on nitrobenzene in soil,and its removal rate reached 95.44%.The mechanism of remove process of nitrobenzene included liquid phase washing,vapor phase evaporation and nZVI reduction.The total removal rates of nitrobenzene using nZVI carryed by water and SDS solution to repair nitrobenzene contaminated soil were 45.65% and 65.64%.The main removal mechanism was liquid leaching and nZVI did not play a important role in reduction. |
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