On the dissolution of hydrated alumina in concentrated solution of sodium hydroxide

Abstract

The most industrial plants for the zeolite production have worked with a sodium aluminate which contains 3-4 wt. % of undissolved alumina. This affects not only the production yield but also increases the production costs requiring additional equipment. The paper considers three simple models, which are applicable to complete dissolution of hydrated alumina as an alumina source in the concentrated solution of sodium hydroxide (26 wt. % NaOH) at 105°C, which are the working conditions in an industrial plant for the production of zeolite 4A. The first model (shrinking sphere model) is based on the rate control by chemical reaction occurring at the particle surface, the second one is based on the rate control by diffusion, whereas the third, mixed-control model, is a combination of these two models. It gives the best agreement with the experimental data, obtained in Holding Institute of General and Physical Chemistry (HIGPC) laboratories.