Structural Change of Montmorillonite by Sulfuric Acid Treatment.

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Ca-montmorillonite from Vici, Oklahoma, U.S.A. is treated with 15% and 35% sulfuric acid at 70°C for 36 hours. With increasing hours, chemical change and morphological alteration are estimated as follows. At first stage, the primary 40Å micropores develop with the extraction of interlayer Ca. At second stage, larger micropores are made as the result of the leaching of octahedral Mg, Fe and Al. The specific surface area becomes maximum of 500m2/g at about 24 hours in case of 15% sulfuric acid treatment and 360m2/g at 9 hours in case of 35% sulfuric acid treatment. At final stage, the primary 40Å micropores disappear and secondary larger micropores remain. As the result, the specific surface area decreases from 360 to 300m2/g in case of 35% sulfuric acid. It is considered that this alteration is caused by the decomposition of montmorillonite structure and the formation of amorphous silica during sulfuric acid treatment.
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