Hydraulic Properties of Polymerized Bentonites

Abstract

With the goal of increasing the swelling pressure and lowering the permeability of ordinary sodium bentonite with high concentration cation solutions, the optimum conditions for producing polymerized bentonite (PB) were examined through a series of laboratory tests. Based on the test results, the proposed optimum conditions for using the free radical polymerization are using sodium acrylate as the monomer and potassium persulfate (KPS) as the initiator, pH of 7, the initiator (I) to monomer (M) ratio, I/M, of .2 and the monomer content of 1%. Then, the PB produced using the proposed conditions was further investigated on the microstructure and the hydraulic properties. The results of X-ray diffraction (XRD) patterns indicate that the sodium polyacrylate did not modify the interlayer spacing of the bentonite particles, but the scanning electron microscopy (SEM) image shows that the PB particles have rounder edge compared with that of the untreated bentonite (UB) particles because the bentonite particles were coated by the polymer. For the hydraulic properties, the results of a swelling pressure test show that with comparable initial dry density, PB had higher swelling pressure than that of the UB. Under the identical void ratio, the PB had much lower permeability (k) than that of the UB with aggressive .6 M NaCl and .6 M CaCl2 solutions. Based on the test results, the PB produced using the proposed conditions can be used as a barrier material against high concentration cation solutions. The proposed optimum condition can be a useful guideline for further investigations on the other properties of the PB.