KINETICS OF GLASS DISSOLUTION AND ZEOLITE FORMATION UNDER HYDROTHERMAL CONDITIONS

Abstract--After a temperature-dependent p riod when little dissolution occurs, the dissolution of rhyolitic glass can be described by dC/dt = k(Cs- C), where Cs is the concentration f dissolved silica at saturation, C is the instantaneous silica concentration, and k is a rate constant equal to 1.6 • 10-5, 3.0 • 10-s, and 4.5 • 10-5 sec-1 at 115 ~ 130 ~ and 140 ~ respectively, in 2 M Na-K carbonate solution at 1 kbar pressure. At 130 ~ a C ~ value of 0.177 M SiO2 is reached in 30 hr, and phillipsite, clinoptilolite, and mordenite begin forming at 34, 64, and 76 hr, respectively, in 2 M CO3, 1:1 NaJK. During glass dissolution and zeolite formation, the concentration ofAI as AI(OH)4- is buffered at 3.7 x 10-4 M by an unidentified phase. The ratio of SiO2 to AI(OH)4- at the onset of zeolite formation is 475. In 2 M CO3 solution, phillipsite crystal