Dissolution kinetics of zinc oxide and its relationship with physicochemical characteristics

Abstract Dissolution kinetics of zinc oxide (ZnO) powders used as feed additives for supplementation in diet of animals is studied in relation to the powder physicochemical characteristics. The fundamental issue of discrimination of reaction-limited or diffusion-limited dissolution into a stirred liquid medium is addressed. Relationships between dissolution kinetics and physicochemical properties are investigated for a set of 34 ZnO samples of various origins. A principal component analysis allows sorting ZnO samples in three clusters having different physicochemical properties. A correlation analysis discloses the most relevant physicochemical characteristics affecting dissolution: density, agglomerate size and specific surface area. Coarse particles dissolve in a reaction-limited process according to their specific surface area. Fine aggregated particles dissolve in 2 steps: reaction-limited dissolution at the surface of ZnO primary particles, followed by diffusion in the quiescent liquid medium between primary particles to the stirred bulk aqueous medium. A reaction-diffusion model is proposed.