Solute Breakthrough Curves for Processed Kaolin at Low Flow Rates

• Published in: Journal of geotechnical engineering Vol. 121; no. 1; pp. 17 - 32
• Main Authors: Shackelford, Charles D, Redmond, Patrick L
• Format: Journal Article
• Language: English
• Published: New York, NY American Society of Civil Engineers 01.01.1995
• Subjects: Applied sciences; Buildings. Public works; Diffusion in solids; Effluents; Electric resistance measurement; Exact sciences and technology; Flow of fluids; Freshwater; Geotechnics; Hydrodynamics; Mathematical models; Mechanical permeability; Sodium chloride; Soil testing; TECHNICAL PAPERS; Water effect, drainage, ground water lowering, filtration; Hydrology; Electrical conductivity; Chemical transport; pH; Clay soil; Hydraulic conductivity; Kaolinite; Porosity; Diffusion; Sodium chloride; Breakthrough curve; Ground water
• ISSN: 0733-9410; 1944-8368
• DOI: 10.1061/(ASCE)0733-9410(1995)121:1(17)

Solute breakthrough curves for a 0.01-M NaCl solution permeated through two compacted test specimens of processed kaolin soil are measured at two volumetric flow rates (2.65 × 10 −4 cm 3 s and 2.65 × 10 −5 cm 3 s) using a flow pump system. Regression analyses of the effluent solute concentrations with two analytical models resulted in hydrodynamic dispersion coefficients D ranging from 1.49 × 10 −6 cm 2 s to 3.95 × 10 −6 cm 2 s for chloride and from 2.11 × 10 −6 cm 2 s to 8.74 × 10 −6 cm 2 s for sodium indicating that diffusion dominated the transport process in the two column tests. The effluent electrical conductance values measured immediately after sampling also tend to reflect the dominance of diffusion on the solute migration process. An observed decrease in effluent pH from between 4.8 and 5.5 during permeation with distilled water to about 4.5 during subsequent permeation with the NaCl solution is consistent with Na + for H + exchange at relatively low pH previously reported for studies involving kaolinite soils. The results of this laboratory study tend to confirm previous field studies that indicate diffusion-dominated transport at the low flow rates common in fine-grained barrier materials.