Comparative kinetic analysis of conventional and ultrasound-assisted leaching of scheelite by sodium carbonate
(School of Metallurgy and Environment, Central South University, Changsha 410083, China)
Abstract: For further comprehending the mechanism of the intensification of ultrasound for extraction, the difference of leaching kinetics between the ultrasound-assisted and conventional sodium carbonate leaching of scheelite was studied, and the corresponding kinetic equations were established. The results indicate that the obtained apparent activation energy with or without ultrasound is same 72 kJ/mol, and both reactions are controlled by surface chemical reaction. By comparing the leaching kinetics of scheelite by Na2CO3, NaOH and Na3PO4 reactants with or without ultrasound, a general conclusion for scheelite hydrometallurgy is obtained. For the process with the formation of compact product layer, the intensification of the tungsten extraction with ultrasound mainly reflects in the stripping and elimination of product layer, corresponding to the transformation of kinetic controlling step from diffusion controlling step and reduction of apparent activation energy. For the one without compact product layer or with a loose and porous product layer, the intensification mainly embodies in the increase of frequency factor, and the controlling step and apparent activation energy of the reaction always remain constant.
Key words: scheelite; kinetics; ultrasound; ultrasonic chemistry; activation energy