MECHANISM OF SILICA-GEL DISSOLUTION IN WATER IN THE PRESENCE OF PYROCATECHOL

The rates of dissolution of silica gel in aqueous alkaline solutions containing pyrocatechol were measured. At pH 10, all of the silica gel was dissolved in the presence of pyrocatechol at 25-degrees-C for 48 h (SiO2 0.3 g and pyrocatechol 0.04 mol in 15 ml of water). The rates of silica-gel dissolution increased with increasing pyrocatechol concentration. Four moles of pyrocatechol were needed to dissolve one mole of SiO2. The rate of dissolution was first order in solid SiO2 concentration. Langmuir-type adsorption of pyrocatechol to the silica-gel surface was assumed to explain the rate dependence on the pyrocatechol concentration.