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

The rates of dissolution of silica gel in aqueous alkaline solutions c ontaining 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 o f silica-gel dissolution increased with increasing pyrocatechol concen tration. Four moles of pyrocatechol were needed to dissolve one mole o f SiO2. The rate of dissolution was first order in solid SiO2 concentr ation. Langmuir-type adsorption of pyrocatechol to the silica-gel surf ace was assumed to explain the rate dependence on the pyrocatechol con centration.