5:15 PM - 6:30 PM
[AGE27-P14] Effects of Cation Exchange on Colloid Transport in Saturated Porous Media
Keywords:Colloidal Particle, Porous Media, Cation Exchange, DLVO Theory
Many studies on the transport of various colloids transports in natural soils have been reported. There are different findings about retention and release of colloidal particles induced by cation exchange reactions at the surface of collector particles. Torkzaban et al. (2013) showed that quantum dot nanoparticles (diam. 1~10 nm) injected to a sand repacked column were released during the cation exchange reaction between calcium ion (Ca2+) and sodium ion (Na+). On the other hand, Bradford and Kim (2010) have indicated that soil colloids (diam. 360 nm) were retained on repacked quartz sand during the Ca2+-Na+ cation exchange reaction. This study investigates the transport behavior of colloidal particles during Ca2+-Na+ cation exchange reaction in the repacked saturated porous media.
One-dimensional column experiments with carboxyl latex (CL) as a model colloid were conducted using repacked Toyoura sand. Experimental procedure for the experiments was as follows. First, a colloidal suspension (2 mmol L-1 CaCl2 solution) with 10.25 mg L-1 was injected to the column (diam. 5 cm, height 6 cm), followed by a colloid-free CaBr2 solution. Then pure water, 10 mmol L-1 NaCl solution, and pure water were sequentially injected. In the experiments, CLs with 500 nm were used as injected colloids. Experiments using NaCl solution with higher concentration (50 mmol L-1) to increase the amount of exchanged cation, and using CLs of smaller particle size (200 nm) were also conducted. Effluents were collected at two minutes interval to determine pH, EC, CL concentration, and ion concentrations. Interaction energies between colloidal particle and sand particle at different solution chemistry were analyzed based on DLVO (Derjaguin-Landau-Verwey-Overbeek) theory.
In all experiments, the effluent concentration remained low when NaCl solution was injected, but it increased rapidly when pure water was introduced. The DLVO calculations suggested that the CLs deposited at the secondary minimum in the total potential energy even when cation exchange occurred. In addition, based on the DLVO calculations, it was suggested that repulsive force between CLs and Toyoura sand surface was dominant during pure water injection and deposited CLs will be released from the Toyoura sand surface.The obtained effluent concentrations of CL showed that even when the extent of exchanged cation was increased (i.e., experiments using 50 mmol L-1 NaCl) or colloid’s particle size was reduced (i.e., experiments using CLs with 200 nm) , colloids did not detach from the sand surface with the cation exchange reaction.
One-dimensional column experiments with carboxyl latex (CL) as a model colloid were conducted using repacked Toyoura sand. Experimental procedure for the experiments was as follows. First, a colloidal suspension (2 mmol L-1 CaCl2 solution) with 10.25 mg L-1 was injected to the column (diam. 5 cm, height 6 cm), followed by a colloid-free CaBr2 solution. Then pure water, 10 mmol L-1 NaCl solution, and pure water were sequentially injected. In the experiments, CLs with 500 nm were used as injected colloids. Experiments using NaCl solution with higher concentration (50 mmol L-1) to increase the amount of exchanged cation, and using CLs of smaller particle size (200 nm) were also conducted. Effluents were collected at two minutes interval to determine pH, EC, CL concentration, and ion concentrations. Interaction energies between colloidal particle and sand particle at different solution chemistry were analyzed based on DLVO (Derjaguin-Landau-Verwey-Overbeek) theory.
In all experiments, the effluent concentration remained low when NaCl solution was injected, but it increased rapidly when pure water was introduced. The DLVO calculations suggested that the CLs deposited at the secondary minimum in the total potential energy even when cation exchange occurred. In addition, based on the DLVO calculations, it was suggested that repulsive force between CLs and Toyoura sand surface was dominant during pure water injection and deposited CLs will be released from the Toyoura sand surface.The obtained effluent concentrations of CL showed that even when the extent of exchanged cation was increased (i.e., experiments using 50 mmol L-1 NaCl) or colloid’s particle size was reduced (i.e., experiments using CLs with 200 nm) , colloids did not detach from the sand surface with the cation exchange reaction.