Co-transport characteristics of graphene oxide and pentavalent arsenic in modified porous media

Arsenic is one of the main elements of heavy metal pollution in farmland soil. In the process of remediation of arsenic-contaminated farmland soil, it is often overlooked that nanoparticles can re-release the bound arsenic, leading to an increase in the effective arsenic concentration. Due to its high specific surface area and strong adsorption capacity, Graphene Oxide (GO) can be used as a carrier of pollutants to carry pollutants and migrate in groundwater environments. However, researches on the transport behavior of anions Arsenic (As(V)) and GO have not been reported. Clay minerals are more active solid components in the soil and play an important role in affecting the migration and transformation of pollutants. Exploring the influence of clay minerals in the soil on the transport behavior of GO and As(V) in porous media is of great significance for improving the theory and model of the fate and transport of nanoparticles and As(V) in the soil, and protecting the soil-groundwater environment. In this study, the influence of clay minerals on the transport behavior of GO and pentavalent As(V) in porous media was investigated. The montmorillonite and kaolinite were used to modify the quartz sand, and the surface characteristics of the modified quartz sand were characterized by a scanning electron microscope and energy dispersive spectrometer. The migration behavior of GO, As(V) and GO-As(V) in 0%, 10%, 30%, and 50% montmorillonite and kaolinite modified quartz sand column was systematically studied by sand column transport experiment. The difference of the effect of different addition ratios on the transport of As(V) and GO was analyzed with the t-test (paired sample test), and the transport behavior of GO colloids in porous media was explained with Darjaguin-Landau-Verwey-Overbeek (DLVO) theory. The research results showed that the kaolinite particles coated on the surface of quartz sand were separated between particles, and the size was different. The montmorillonite particles coated on the surface of the quartz sand were stacked layer by layer in the shape of an amorphous sheet with a pore-shaped structure. GO and As(V) alone had high mobility in porous media. GO and As(V) both had high mobility in pure quartz sand column, and the recovery rates were 96% and 94%, respectively. The proportion of kaolinite and montmorillonite modified quartz sand added was increased to 10%, 30%, and 50%. The migration ability of GO and As(V) all showed a decreasing trend, there were significant differences in the migration curves of GO and As(V) under different conditions (P<0.05). The recovery rate of GO in the 50% kaolinite modified quartz sand column was 14% lower than that of the quartz sand column, and the recovery rate in the montmorillonite modified quartz sand column was reduced by 17%, while the As(V) decreased by 15% and 12% respectively. When both GO and As(V) existed in the solution, the Zeta potential of GO decreased from -21.3 to -26.7 mV. The presence of As(V) increased the negative charge carried on the GO surface and increased the repulsive force with the surface of the medium. On the other hand, it showed that GO could be used as a carrier of As(V) to carry As(V) for migration. Therefore, the migration ability of GO and As(V) in kaolinite and montmorillonite modified quartz sand was greater than their transport alone. The analysis showed that the mobility of As(V) in the montmorillonite modified quartz sand column was greater than that of kaolinite modified quartz sand, while the mobility of GO was opposite. When both GO and As(V) existed in the solution, the mobility of both in the medium was greater than their transport alone. The transport behavior of GO in packing modified quartz sand with different proportions was consistent with the DLVO theory. This study showed that they could accelerate the transport of As(V) and caused the expansion of soil arsenic pollution after GO and As(V) being released into the porous media.