Co-transport of chromium(VI) and bentonite colloidal particles in water-saturated porous media: Effect of colloid concentration, sand gradation, and flow velocity

The transport of pollutants inside the groundwater system is profoundly affected by absorption and transmission via colloid or soil particles. Therefore, it is essential to investigate the significant pollutants (Such as hexavalent chromium (Cr(VI))) transfer in the presence of colloid particles that can facilitate or retain this transfer. For this purpose, an experiment is carried out in a saturated porous media column to study the bentonite concentration, flow velocity and sand grain size effects on co-transport of Cr(VI) with bentonite. The results of this study demonstrated that the colloid particles facilitate the transfer of Cr(VI) by 30% in 200 mg/l bentonite colloids concentration. The amount of transmitted Cr(VI) is decreased by increasing the bentonite colloids concentration from 200 mg/l to 300 mg/l. As the flow velocity increased from 2 cm/min to 3.3 cm/min, the amount of transferred Cr(VI) increased by 7%. The results show that with reducing the sand grain size, the amount of transmitted bentonite and Cr(VI) is reduced that this effect is more sensible in bentonite transport. As a result, it can be noted that the bentonite colloidal particles according to its concentration and experimental conditions, may facilitate or retain the Cr(VI) transport and sand gradation has a significant impact on colloid and pollutant transmission.