Dissolution of amorphous aluminosilicate zeolite precursors in alkaline solutions. Part 2.—Mechanism of the dissolution

Abstract

The influence of the initial mass of the solid phase and concentration of NaOH on the kinetics of dissolution of an amorphous aluminosilicate precursor having an Si : Al molar ratio of 1.178 : 1 has been studied by measuring the change in the aluminium and silicon concentrations in the liquid phase during dissolution at 80 °C. Analysis of the results obtained indicated that only the outside surface and not the internal surface (pore system) is relevant in the dissolution process. The process of dissolution is controlled by two reactions: a forward one, whose rate is proportional to the outer surface area, S, of the solid phase exposed to the action of OH^– ions from the liquid phase, and a backward one, whose rate is proportional to the surface area, S, and to the concentration of reactive silicate and aluminate species from the liquid phase.