The leaching mechanism of niobium from a refractory niobium-tantalum ore by concentrated potassium hydroxide was studied. The effects of stirring speed, reaction temperature, mass ratio of alkali-to-ore, initial potassium hydroxide concentration and particle size on the leaching rate of niobium were reported. The results show that the leaching rate is direct proportional to the inverse square of particle diameter, and the experimental data of the leaching rate are fit to the Crank-Ginsting-Braunshtein’s diffusion-through-layer-reaction-control model,that is: 1+2(1-X)-3(1-X)2/3=kt. According to the Arrhenius expression, the apparent activation energy for the leaching of niobium is 72.2kJ?mol?1. Based upon the result of the kinetic experiment as well as the SEM and EDAX analysis results, it is proved that during the leaching process of niobium-tantalum ore by concentrated potassium hydroxide, a solid product layer is formed on the surface of the unreacted core and its main composition elements are iron and manganese, the diffusion of [(Nb,Ta)6O19]8? through that layer is presumed to be the rate-controlling step of the leaching proces. The results obtained in this paper provide important basis for the strengthening of the leaching process.
Journal of Chemical Engineering of Chinese Universities
concentrated potassium hydroxide