Experiment on Influence of Flow Velocity and Medium Particle Size on As(Ⅲ)Migration
To understand the influence of groundwater velocity and medium particles on As(Ⅲ)migration in the riparian zone,natural river sand is selected as the medium,and groundwater solutions containing As(Ⅲ)as commonly seen in some riparian zones are prepared to carry out batch experiments and dynamic column experiments.Combing with the characterization analysis,the influence and mechanism of velocity and medium particle size on As(Ⅲ)migration are discussed.The results show follows:(1)The adsorption equilibrium time of As(Ⅲ)is longer for the smaller particle size of river sand.The equilibrium adsorption capacity(Qe)of As(Ⅲ)on the river sand decreases with the increase of its particle sizes(except for river sand with a particle size of 0.15-0.18 mm),and the maximum amount(Qm)of monolayer adsorption shows a decreasing trend with the increase of particle size.(2)As(Ⅲ)migration in the column filled with river sand is significantly affected by the particle size and velocity.On one hand,the river sand of the smaller particle size has a larger specific surface area,which usually leads to longer interaction time between aqueous solutions and solid medium,thus limiting the groundwater flushing rate.This is not conducive to the migration of As(Ⅲ)in river sand.On the other hand,the higher flowing velocity leads to a stronger hydraulic shear force in the void channel.Meanwhile,the increase of turbulence intensity reduces the thickness of the retained boundary layer,which is conducive to the migration of As(Ⅲ)in river sand.
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