Study On Nano-SiO₂ Stabilized Foam Enhanced Removing Nitrobenzene From Groundwater

In recent years,the unreasonable disposal and discharge of a large amount of solid waste and organic wastewater have caused extremely serious environmental pollution.Because of its stable structure,nitrobenzene is not easily biodegraded in the environment.It can enter the human body through direct contact,respiratory inhalation,etc.,it is a typical organic pollutant with high toxicity and refractory degradation.Many countries list it as one of the“priority pollutants”.The repair of nitrobenzene-contaminated groundwater is one of the hot issues that need to be solved urgently.Surfactant-enhanced remediation technology is a simple,quick-acting and short-term repair method,but the surfactant is easy to produce channel effect when using,that the eluent will preferentially flow along the channel with higher permeability,while the area with low permeability has limited repair effect.In addition,because of the leaching enhances the fluidity of the contaminants,it also increases the possibility of an enlarged contaminated area.Many scholars have prepared surfactants into foams,replacing the eluent in the form of a gas-liquid mixed system of foam.The foam has the advantages of low density and easy control,thereby avoiding the pore effect and the enlargement of the contaminated area.At present,most of the researches are carried out on the scale of macroscopic simulation columns and simulated tanks.,but the research on the migration of foams and the process of removing nitrobenzene has not been studied.In addition,in the study of the effect of strengthening the repair of foam,the foam is mostly used as a carrier to carry the repairing agent,and there is little research to improve the performance of the foam itself.The experimental research in this paper consists of two parts:first,the medium-pore model was used to study the migration behavior of foam in porous media and the mechanism of removing nitrobenzene,and based on this,a method for strengthening foam repair was proposed;secondly,using hydrophobically modified nano-SiO₂ to improve the stability of foam,research the migration of stability foam in porous media and the ability to remove contaminants.The main conclusions are as follows:?1?The formation,destruction and migration of foam in porous media occur simultaneously;the formation includes three modes:liquid film lag,neck separation and film segmentation;Gas diffusion is the main way of foam collapse;The foam is mainly transported in the form of a bubble chain,and most of the foam is trapped by the pores of the medium.?2?Compared with surfactant solution,foam has a larger spreading area in porous media and is more capable of removing nitrobenzene.Foam removes pollutants by blocking,emulsifying and stripping,of which plugging is the most important way to remove them.?3?Nano-SiO₂ can enhances the stability of the foam.The reason for the enhancement is that the hydrophobic properties of the nanoparticles change their relative positions in the foam,and it is easy to form a dense shell film on the surface of the liquid film,thereby weakening the gas diffusion;Nitrobenzene has less effect on hydrophobic SiO₂-stabled foam.?4?When the foam migrates in the porous medium,the pressure at each point changes linearly,and the pressure value tends to a stable value with the increase of the foam injection;The injection pressure of the foam is independent of the injection rate of the foam and the concentration of SiO₂,while the particle size is related.The larger the particle size is,the smaller the injection pressure is,and the smaller the particle size is,the larger the injection pressure is.The injection pressure will eventually become a stable value with the injection of foam.The faster of the injection and the larger of the concentration of SiO₂ is,the faster the stability is achieved.The nano-SiO₂ is used as a stable material and the foaming liquid to form a foam into the porous medium,which has little effect on the permeability of the porous medium.After the stable foam injection,the permeability of the porous medium coefficient becomes 85-90%of the original.?5?The main way in which foam removes contaminants is displacement,followed by dissolution.Water,Separate Surfactant,Foam and Nano-Silica Stabilized Foam,the ability to remove Nitrobenzene:SiO₂ Foam>SDS Foam>SDS>Water;When the injection flow rate is low,the ability of SiO₂ foam to remove nitrobenzene is stronger than when the injection flow rate is higher,because the lower the flow rate,the more chance the foam has more contact with the contaminants,thereby improving the removal efficiency;SiO₂ foam requires different injection pressures in different media,and the ability to remove pollutants nitrobenzene is different,and the removal ability is:gravel>coarse sand>medium sand>fine sand.