Expandability-layer stacking relationship during experimental alteration of a Wyoming bentonite in pH 13.5 solutions at 35 and 60(omicron)C

The reaction of a Wyoming-type bentonite with pH 13.5 solutions was investi gated experimentally at 35 and 60 degreesC for periods of 1 to 730 days. So me crystal properties of the starting montmorillonitic clay remain unchange d, i.e, stability of the octahedral sheet, total cation exchange capacity ( CEC) and CEC after neutralization of the octahedral charge, full expandabil ity in the Ca-saturated state, and size distribution. Other properties are changed, e.g. there is an increase in the expandability after octahedral ch arge neutralization; a slight increase in the average layer charge; a decre ase of the total surface area; and a particle morphological change from fla kes to hexagonal shape. The composition and the structure of the smectite layers did not change sig nificantly during the reaction. The increasing number of expandable layers after octahedral charge neutralization is attributed to modifications in th e stacking sequence. The number of interlayers surrounded by two charged te trahedral sheets increases with reaction time.