Liquid Phase Mass Transfer of ZnO-Acid Solution Systems in an Agitated Vessel

Abstract

Experimental and theoretical studies on the initial leaching rate of a spherical pellet of ZnO in HA (A = ClO₄, NO₃, Cl), HA-ZnA₂ and HA-NaA solution have been made to discuss the characteristics of liquid phase mass transfer for ZnO-acid solution systems in an agitated vessel.
The results obtained are as follows:
(1) For the ZnO-HA systems, the leaching rate is proportional to the concentration of acid and 0.6 power of stirring rate, and also is the same for three different acids.
(2) For the ZnO-HA-ZnA₂ systems, the rate is same for three different acids and increases with concentration of ZnA₂. At high concentration of ZnA₂, however, the rate is different for each acid.
(3) For the ZnO-HA-NaA systems, the rate is the same for three different acids, and increases with NaA concentration.
(4) The results of dissolution rate of benzoic acid into aqueous solution and leaching rate for the ZnO-HA systems show that the leaching process for the systems studied is controlled by the liquid phase mass transfer.
(5) The rates calculated by a mass-transfer model based on a film theory involving diffusion and electrical migration are consistent with the experimental ones for the ZnO-HA, ZnO-HA-NaA and ZnO-HA-Zn (ClO₄)₂ systems.
For the ZnO-HA-Zn(NO₃)₂ and the ZnO-HA-ZnCl₂ systems, the calculated values are not consistent with the experimental ones at a high concentration of ZnA₂, although the model gives good agreement between the two values at a low concentration of ZnA₂.