Impact of organic contaminant viscosity and cation hydrated radius on the rheological properties of sodium-bentonite: experimental and numerical investigations

Abstract

Soil contamination by organic and hazardous substances is a critical environmental issue, particularly in developing countries. This study investigates the limitations of double-layer theory for bentonite–organic contaminant interactions through experimental and numerical analysis. Using NaCl and KCl as salts and acetone, isopropyl alcohol, and glycerol as organic contaminants, the research explores the rheological properties of Na-bentonite dispersions. The double-layer theory, particularly Stern's model, has limitations in accurately representing the interaction between bentonite and organic contaminants. The research aims to validate the double-layer equations and investigate the impact of viscosity and cation hydrated radius on the rheological properties of Na-bentonite. The novelty lies in introducing a range of viscosities into the pore fluid to challenge existing double-layer equations. Numerical calculations based on double-layer theory were used to analyze the total interaction energy. The study found that without salt, bentonite showed similar rheological behavior in acetone and alcohol but higher yield stress in glycerol. NaCl up to 0.1 M increased yield stress, while 0.5 M reduced it. KCl had a more pronounced effect on rheological properties than NaCl, highlighting the importance of cation hydrated radius. In soil-organic mixtures, lower viscosity organic chemicals increased yield stress. Despite similar dielectric constants, acetone showed higher yield stress than glycerol at lower concentrations, but at higher concentrations, dielectric constant differences became dominant. The study confirms the limitations of double-layer theory in bentonite–organic contaminant interactions, particularly regarding pore fluid viscosity, though it remains reliable at high contaminant concentrations.