IMPACT OF OZONE ON STABILITY OF MONTMORILLONITE SUSPENSIONS

A sodium montmorillonite (NaM) suspension (150 mg/liter) was treated with various ozone doses up to 97 μM (0.65 μmol O3/mg NaM). Suspension stability increased with increasing levels of ozonation as evidenced by increases in critical coagulation concentration (CCC) values of Na+, Ca2+, and La3+. The increase in induced stability of NaM was found to be most pronounced with Na+ as an indifferent electrolyte and least noticeable when La3+ was used. The enhanced stability of NaM can in large measure be attributed to an increase in the surface charge as a result of ozone-induced transformations. The conductivity of the suspending medium (water) was found to increase with ozonation indicating a leaching of ions from the crystal structure. DLVO theory was utilized to interpret the stability behavior of NaM suspensions; however, it underestimated CCC values. This discrepancy was attributed to an additional force resulting from hydrogen-bonding interactions. These interactions were found to be repulsive (hydration pressure) in nature. Hydration pressure increased with ozonation while Liftshitz-van der Waal forces remained largely unaffected. Electrostatic forces were found to be the major component responsible for increased stability of NaM as a result of ozonation, supporting a crystal dissolution hypothesis. © 1992.