Mechanisms And Influencing Factors Of The Transport Of Carbon Nanotubes In Porous Media

Carbon nanotubes (CNTs) have the potential to be released into the environment during their life-cycles which may pose contamination risks to the underground water and soil. Assessing the risks of CNTs in the environment requires an understanding of their transport in the environment. Soil is the center of whole ecosystem, contacting with the hydrosphere, atmosphere and lithosphere and soil properties such as soil grain size, texture, types of minerals and organic matter content could affect the transport of CNTs. In this study, we firstly used quartz sand simulating soil environment to explore the transport of multi-walled carbon nanotubes (MWCNTs) suspended by three kinds of surfactants (sodium dodecylbenzene sulfonate-SDBS, octyl-phenol-ethoxylate-TX-100and cetylpyridinium chloride-CPC) and the influence factors of the MWCNTs transport; then, we conducted the laboratory column experiment to assess transport and retention of the MWCNT suspended by the three surfactants in four natural soil-packed columns, and focused on the effect of soil grain size, soil texture and the content of organic matter on the MWCNT transport. The main results are as follows:(1) Three surfactants-CNT could break through the sand-packed columns and the transport ability had an order of CPC-CNT> SDBS-CNT> TX-100-CNT; however, CPC-CNT could hardly break though all the soil-packed columns (including laterite of Hainan-HN, loess of Xian-XA, sediment of Hangzhou-HZ, black soil of Heilongjiang-HLJ) while SDBS-CNT and TX-100-CNT could transport through the HN, HZ and HLJ columns but none of them could transport through the XA column.(2) The MWCNT transport increased with increasing grain size and decreasing clay content of the soil samples; high flow velocity was favorable for the transport of MWCNTs, while high Ca2+concentration and low pH were unfavorable for the transport; soil organic matter (SOM) could inhibit the transport of positively charged CPC-CNT while it had insignificant effect on the transport of SDBS-CNT and TX100-CNT.(3) Electrostatic interactions could affect the transport of MWCNTs in the porous media columns, the adsorption of the positively charged CPC-CNT on the negatively charged porous media occured owing to electrostatic attraction and the elute of CPC-CNT concentration kept slow rising because of site blocking; MWCNT aggregates deposited on the surfaces of porous media and in the pore throats because straining occurred in the small pores, which further decreased the transport of MWCNTs and made the breakthrough curves present parabolic because of ripening.