Transport Of Nano Materials And The Effect Of Nano Materials On Transport Of Cd²⁺ In Saturated Porous Media

With the development of nanotechnologies and the wide use of nanomaterials,nanomaterials could inevitablely enter the natural environment. It is still not clear whether theunique particle sizes and surface characters of nanomaterials will change the transport processof some materials in the soil environment or not. Therefore, in this research, two typicalinorganic nanomaterials----Carbon nanotubes (CNTs) and nano-SiO2(nSiO2) were chosen asthe study objects. The adsorption characteristics of amino modified nSiO2for Cd2+in aqueousenvironment have been discussed by batch experiments. The column tests have beenconducted to study the transport behavior of nanoparticles, and the effect of nanoparticles onthe transport of Cd2+in saturated porious media was investigated as well. This research issignificant for discussing the transport and retention of nanomaterials in the environment. Themain results could be concluded as following:(1) Silane reagents3-(2-Aminoethylamino) propyl]-trimethoxysilane and EDTA wereused to modify nSiO2to get amino and EDTA modified nSiO2(2N-nSiO2, EDTA-nSiO2).The particle size, specific surface area, porous size and porous volumn of modified nSiO2hadchanged while the regular spherodial appearance of nSiO2did not change. The amino andcarboxyl on the modified nSiO2contribute to more active adsorption sites for Cd2+adsorption,which increased the adsorption ability of nSiO2for Cd2+in aqueous environment. Theadsorption ability of modified nSiO2for Cd2+was higher than the raw nSiO2and themaximum adsorption amount of2N-nSiO2and EDTA-nSiO2for Cd2+were0.07and0.12mol/L respectively.(2) Different concentrations of NaNO3, acetic acid, tartaric acid and citric acid wereadded to the MWCNT and nSiO2suspension to study their effect on the transport of MWCNTand nSiO2in saturated porous media. The results showed that the transport of MWCNT wasvery sensitive to the solution chemistry. The mobility of MWCNT decreased with theconcentrations of NaNO3, acetic acid, tartaric acid and citric acid increasing. Compared withother three organic acids, acetic acid had the weakest influence on the transport of MWCNT.As for the nSiO2, NaNO3had significant influence on its mobility while the organic acids hadno remarkable effect unless under high concentrations. (3) The effect of2N-nSiO2on the transport ot Cd2+study showed that when the2N-nSiO2adsorbed Cd2+or transported together with Cd2+, their mobility of2N-nSiO2reduced and its retention increased with the increase of Cd adsorbed on the surface of2N-nSiO2or in the solution. When the Cd transported together with2N-nSiO2, its mobilityalso decreased and this decrease was more obviously with the low Cd concentration. Becauseof the adsorption ability of2N-nSiO2, there were less Cd transporting through the columnwhen the sand loaded some2N-nSiO2. At the same time, the2N-nSiO2can also desorb Cdfrom the sand during its transportation through the sand column.