Optimization And Verification Of Nanoparticles Transport Model In Medium

Nanomaterials have been widely used in the fields of life science,soil remediation,water treatment,agricultural fertilizer and energy due to their special physical and chemical properties.However,most of them will eventually enter the soil,groundwater and other natural environments,which may inevitably present potential environmental risks.Therefore,it is of great significance to study the transport,fate and factors affecting the migration of nanoparticles in these natural media for the protection of soil and groundwater environment.And nanomaterials have a wide application prospect in soil pollution remediation.The transport of nanoparticles in porous media such as soil is currently predicted by models that are simply based on single-collector removal efficiency(?).The single-collector removal efficiency(?) is influenced by many factors,such as the properties of nanoparticles themselves,the properties of porous media and the properties of fluids.And this efficiency only considers the collecting effect of a single solid matrix,and does not consider the trapping effect of the pore space between the porous media.In view of this,this thesis focuses on the pore characteristics of porous media to study the transport of nanoparticles in porous media.Firstly,the limitations of the classical transport model(T-E model) in application are revealed and analyzed.The experimental results show that the relationship between the impact efficiency(?₀) of nanoparticles in porous media and porosity(f) is not the one-to-one correspondence as thought in the T-E model for the same porosity.Instead,the same porosity(f)corresponds to different collision efficiency(?₀).This is mainly because the T-E model ignores the effect of the pore characteristics of porous media,namely the arrangement of porous media.In order to quantify the effect of pore characteristics on nanoparticle transport,water retention capacity(f_r) was used to quantitatively reflect the pore characteristics of medium particles.It was found that when the porosity(f) of the porous media was the same,the penetration rate of nanoparticles to the porous media was still different,but was negatively correlated with water retention capacity(f_r).On this basis,the T-E model was modified by introducing the pore characteristic parameter F(F=f_r/f).The collector contact efficiency by the interception mechanism(?_I)is adjusted to be dependent on both porosity(f)and water retention capacity(f_r).Thus,the original model was optimized.The new model fully considers the effect of pore characteristics on the transport of nanoparticles in porous media.At the same time,the rationality of the data after the optimization model was compared through the transport experiments of nano-silica(nSiO₂),nano-iron oxide(nFe₃O₄) and nano titanium dioxide(nTiO₂) in sand column.In this study,the effects of the pore characteristics on the mobility of nanoparticles were investigated by adjusting the pore characteristics of porous media by earthworm movement and stirring.The validity of the model was evaluated by comparing the stability of attachment efficiency(?) obtained from different transport experiments.The attachment efficiency of nanoparticles in porous media calculated by the optimized model are all close to a certain value.It was proved that the optimized model is more accurate in predicting the transport of nanoparticles in porous media.Finally,the transport experiments of nano-sized titanium dioxide(nTiO₂) in porous media were taken as an example.Under the condition of clear water retention capacity(f_r) and porosity(f),the influence of various factors was investigated.The results of transport experiments showed that the increasing degree of agglomeration and concentration of nanoparticles led to a decrease penetration rate.The porous media with rough surface could attach more nanoparticles,thus reducing the penetration rate of nanoparticles.The porous media with small particle size led to a lower penetration rate of nanoparticles.The penetration rate of nanoparticles was higher with higher flow rates.And the higher ionic strength condition could reduce the penetration rate of nanoparticles.