A kinetic study of the leaching of a low-grade niobium–tantalum ore by concentrated KOH solution

A kinetic study of the leaching of a low-grade niobium–tantalum ore by concentrated KOH solution under atmospheric pressure has been investigated. The effects of reaction temperature, KOH concentration, agitation speed, particle size and alkali-to-ore mass ratio on the dissolution rate of niobium were examined. It was found that the dissolution rate of niobium is significantly influenced by the temperature, particle size and concentration of KOH solution. The experimental data were well interpreted with a shrinking core model under diffusion control through the product layer. By using the Arrhenius expression, the apparent activation energy for the dissolution of niobium was evaluated. Finally, on the basis of the shrinking core model, the following rate equation was established: 1 − 3 ( 1 − X b ) 2 / 3 + 2 ( 1 − X b ) = k 0 R 2 e − 72200 R ′ T · t .