Influence of hydrodynamic factors on the migration of arsenic in river sand: Column experiment and models

The riparian zone is a typical groundwater-surface water interaction zone, and there are few research reports on the behavior of arsenic in this interaction zone under different hydrodynamic conditions. In this study, the river sand samples from the riparian zone are collected to carry out indoor column experiments, the influence of different hydrodynamic factors (including flow velocity and particle size) on the migration of arsenic in the river sand are analyzed, and related models are established. The results show that (1) at a flow rate of 0.5 mL/min, the adsorption rate of the river sand on As(V) and the time required to reach an equilibrium state are both faster than those on As(III), and the smaller the particle size, the more obvious the phenomenon; at a flow rate of 1.0 mL/min, the adsorption rate of the river sand with different particle sizes on As(V) increases with the increasinng particle size, but there is no significant difference in the adsorption of As(III). (2) In a packed column filled with sand of the same particle size, the adsorption capacity of the river sand for As(III) and As(V) decreases with the increasing flow velocity. (3) Under the conditions of different flow rates and particle sizes, the migration processes of As(III) and As(V) in the sand column are more in line with the Thomas model, and the fitting R² are higher than those of the Yoon-Nelson and Adams-Bohart models under the same conditions. Among them, at low flow rates, the Thomas model fitting R² (≥0.94) to the migration processes of As(III) and As(V) in the particle size of 0.15−0.25 mm are significantly better than that of the larger particle size of 1.00−2.00 mm. At high flow rates, the model has little difference in fitting R² to the migration process of arsenic in different particle sizes.