Abstract
Influences of sodium hydroxide and sodium aluminate concentrations, stirring velocity, temperature and particle size of the ores were studied. The leaching reactions gradually proceed with the prolonged leaching time. The leaching rates are accelerated by increasing the sodium hydroxide concentration and the surface area. The apparent activation energies calculated from the Arrhenius plots are 19.6, 17.1, 10.5 and 12.5kcal/mol for gibbsite, boehmite, Seaba ore and Comalco ore respectively. The leaching rates are independent of the stirring velocity and addition of sodium aluminate into the leaching solution. The rate-determing step in the leaching reactions of gibbsite, boehhite and buxite ores is a chemical reaction process rather than mass transport one. The leaching rates for gibbsite and boehmite are expressed as K.A.CNaOH. exp (-19600/1.987T) and K.A.CNaOH. exp (-17100/1.987T) respectively, where K is the rate constant, A the surface area of aluminumhydroxide, CNaOH the sodium hydroxide concentrationand T the absolute temperature.
