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Salinity effect on swelling characteristics of compacted bentonite

Shirazi S. M., Wiwat S., Kazama H., Kuwano J., Shaaban M. G.

Environment Protection Engineering

2011

Vol. 37, nr 2

65-74

Swelling characteristics of compacted bentonite is the most important factor for nuclear waste disposal facilities. Salinity effect on swelling behaviour of compacted bentonite was investigated experimentally. A series of one dimensional swelling deformation tests have been performed. The tests were conducted for various initial dry densities from 1.33 g/cm3 to 1.90 g/cm3 for compacted bentonite saturated with NaCl of various concentrations in solution from 0 to 4.0 M. It was found that initial dry density and concentration of NaCl strongly influence the swelling rate of bentonite. The swelling rate of bentonite decreases with increasing the concentration of NaCl. Swelling rate depends on the concentration of NaCl more than on initial dry density and loading effect. Bentonite may change from highly swelled material to coagulate in saline water. Liquid limit of bentonite is also remarkably decreased with the change of liquid from distilled water to saline one, while the plastic limit is slightly increased.

Effect of Initial N,N'-Methylene Bisacrylamide Concentration on the Swelling Behaviour of Acrylic-based Superabsorbent Polymers

Mucientes A., Santiago F., Delgado A.

Polish Journal of Chemistry

2005

Vol. 79 / nr 5

897-905

Aseries of superabsorbent polymers based on acrylic acid has been synthesized by a solution polymerization technique at 60°C. The effect of the N,N_-methylene bisacrylamide concentration on the swelling behaviour of these hydrogels in deionized water and saline solution was investigated. Experimental results indicate that the absorbance in deionized water or saline solution decreases on increasing the concentration of crosslinker. Moreover, the amount of swelling in 0.2 wt% NaCl(aq) is smaller than that in deionized water, a result that is due to the decrease in the osmotic pressure (ionic pressure) difference between polymer and external solution at high ionic strength. High swelling and appropriate absorption kinetics can be obtained by altering parameters such as initial monomer concentration, range of neutralization, temperature, initiating system and range of crosslinker concentration. These changes were studied but are not reviewed here. Rates of swelling for these absorbents were found to fit the Voigt expression. Relationships were also established between the ultimate degree of swelling and the ratio of crosslinker to monomer. The results of the investigation involving water or saline solution diffusion in hydrogels approximate to Case II sorption in the early stages of the swelling process and to Case I in the later stages.