10:45 AM - 12:15 PM
[AGE27-P13] Effects of Cation Exchange on Colloidal Particle Behavior near Solid-Water Interface
Keywords:colloid, cation exchange, interaction force, microfluidic channel
Nano and micro scale particles (colloidal particles), including clay minerals and humus, exist in soils. These colloidal particles are known to act as a carrier for pollutants and various ions, leading to colloid-facilitated contaminant transport. Therefore, it is essential to understand the transport behavior of colloidal particles in soils. Previous researches have revealed that the behavior of colloidal particles in porous media is affected by various factors such as the properties of the colloidal particles, solution chemistry in pore water, and flowing condition. However, the colloidal behavior during the cation exchange reaction occurring on the collector (i.e., grain) surface is not well understood. In this study, colloidal particle behavior near the solid-liquid interface during the cation exchange reaction was investigated by measuring the interaction force between colloid and collector surfaces using an atomic force microscope (AFM) and colloidal transport experiments using a microfluidic channel.
In this study, fluorescent carboxylate latex (CL) was used as model colloids. In the AFM measurements, the interaction forces between the silica plate and probes with a CL particle attached to the cantilever were measured. The force-distance curves of colloidal particles during approach and separation were obtained in four solutions: 10 mM NaCl solution, 2 mM CaCl2, MgCl2, and ZnCl2 solution. After obtaining force-distance curves in 2 mM CaCl2 solution, force-distance curves were also obtained by exchanging the solution with 10 mM NaCl solution. The microfluidic model had a channel 60 mm long, 1.4 mm wide, and 0.05 mm deep, with pillars 0.2 mm in diameter at 0.11 mm intervals. The CL suspension (4.55×107 particles mL-1) was prepared by adding CL particles with a particle size of 1 micron to the solution (2 mM CaCl2, 2 mM ZnCl2, and 10 mM NaCl). The CL suspension was injected to the microfluidic channel at a constant flow rate of 0.50 mL min-1, followed by the solution without CL, deionized water (DI) water, 10 mM NaCl solution, and DI water.
The AFM measurements showed that adhesion forces between CL particles and silica plate were present in Ca and Zn solutions, which were not observed in Na solutions. Furthermore, electrostatic repulsion increased with solution exchange from Ca to Na solutions. In the microfluidic channel experiments, the incremental increase of the average number of colloids deposited per pillar, representing CL deposition efficiency, was higher in the Ca and Zn solutions than in the Na solution. In addition, the deposition efficiency was higher in the lower pH condition. These results were consistent with the measurement of electrostatic repulsion between CL particles and silica plate using AFM. No release of deposited CL particles was observed during solution exchange from Ca to Na solution (i.e., cation exchange reaction) or during DI water injection. It was suggested that hydrodynamic drag force was significant in the microfluidic channel, resulting in less colloidal deposition under Ca solution and the attractive force between the colloidal particles deposited under these conditions and the pillar surface was so strong that the cation exchange reaction was unaffected.
In this study, fluorescent carboxylate latex (CL) was used as model colloids. In the AFM measurements, the interaction forces between the silica plate and probes with a CL particle attached to the cantilever were measured. The force-distance curves of colloidal particles during approach and separation were obtained in four solutions: 10 mM NaCl solution, 2 mM CaCl2, MgCl2, and ZnCl2 solution. After obtaining force-distance curves in 2 mM CaCl2 solution, force-distance curves were also obtained by exchanging the solution with 10 mM NaCl solution. The microfluidic model had a channel 60 mm long, 1.4 mm wide, and 0.05 mm deep, with pillars 0.2 mm in diameter at 0.11 mm intervals. The CL suspension (4.55×107 particles mL-1) was prepared by adding CL particles with a particle size of 1 micron to the solution (2 mM CaCl2, 2 mM ZnCl2, and 10 mM NaCl). The CL suspension was injected to the microfluidic channel at a constant flow rate of 0.50 mL min-1, followed by the solution without CL, deionized water (DI) water, 10 mM NaCl solution, and DI water.
The AFM measurements showed that adhesion forces between CL particles and silica plate were present in Ca and Zn solutions, which were not observed in Na solutions. Furthermore, electrostatic repulsion increased with solution exchange from Ca to Na solutions. In the microfluidic channel experiments, the incremental increase of the average number of colloids deposited per pillar, representing CL deposition efficiency, was higher in the Ca and Zn solutions than in the Na solution. In addition, the deposition efficiency was higher in the lower pH condition. These results were consistent with the measurement of electrostatic repulsion between CL particles and silica plate using AFM. No release of deposited CL particles was observed during solution exchange from Ca to Na solution (i.e., cation exchange reaction) or during DI water injection. It was suggested that hydrodynamic drag force was significant in the microfluidic channel, resulting in less colloidal deposition under Ca solution and the attractive force between the colloidal particles deposited under these conditions and the pillar surface was so strong that the cation exchange reaction was unaffected.