Effect of pH Variations on the Yield Stress of Calcium Bentonite Slurry Treated with pH-Responsive Polymer

Hyunwook Choo,Changho Lee,Woojin Lee,Youngmin Choi

doi:10.3390/ma13112525

Abstract

The pH-responsive polymers, such as polyacrylamide (PAM), show distinct conformational states according to the pH of their environmental groundwater. Therefore, the interactions between clay–polymer and polymer–water molecules, which determine the yield stress of bentonite–polymer composites, can be affected by the pH of groundwater. This study aims to evaluate the effect of pH variation on the yield stress of calcium bentonite treated with PAM. The yield stresses (τy) of untreated and PAM treated clays were measured with varying volume fractions of solid (VF = 10–23%) and under varying pH conditions (pH = 7.6–9.6). In addition, the zeta potential was measured for both untreated and treated clays to figure out the change in the surface charge of the mineral surface due to PAM treatment. The results of this study demonstrate that τy for treated clay is higher than that for untreated clay at a given VF, because van der Walls attraction dominates electrostatic repulsion in the case of treated clay. Due to the change in conformational states of PAM and the consequent change in surface charge that comes with varying pH, the pH-dependent change in τy of treated clay is significantly different from that of untreated clay.

Highlights

Bentonite slurry has been widely used for various engineering purposes, such as slurry walls, grouts, and boring fluids, due to its low hydraulic conductivity and high swelling characteristics. sodium bentonite is widely used due to its superior engineering performance, natural deposits of calcium bentonite are globally more common than those of sodium bentonite [1,2]
To satisfy engineering requirements, a low-quality calcium bentonite is typically admixed with additives, such as phosphate [8,9,10], sodium carbonate [11], and polymer [3,12]
For the PAM treated specimen, the peak stress was not observed in the stress–time curve under the tested solid contents and pH

Summary

Introduction

Bentonite slurry has been widely used for various engineering purposes, such as slurry walls, grouts, and boring fluids, due to its low hydraulic conductivity and high swelling characteristics. sodium bentonite is widely used due to its superior engineering performance, natural deposits of calcium bentonite are globally more common than those of sodium bentonite [1,2]. Bentonite slurry has been widely used for various engineering purposes, such as slurry walls, grouts, and boring fluids, due to its low hydraulic conductivity and high swelling characteristics. To satisfy engineering requirements, a low-quality calcium bentonite is typically admixed with additives, such as phosphate [8,9,10], sodium carbonate [11], and polymer [3,12]. When the bentonite slurry is employed as a grout material, its rheological properties, such as yield stress and viscosity, are very important. It is well known that the yield stress of bentonite slurry can be affected by a number of parameters, including the clay concentration, type of bentonite, molar ratio of Na/Ca, microstructure, electrolyte concentration, and pH [9,11,17,18,19,20]

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Conclusion