Effect of temperature on the solubility and solid phase stability of zirconium hydroxide

Abstract

Summary The solubility and solid phase stability of zirconium hydroxide was investigated in the acidic pH range after heating the aqueous samples at 50, 70 and 90 ◦C. The solubility measured at room temperature after exposing the batch samples to elevated temperatures for a given period of time significantly decreased with increasing heating periods. The Zr concentrations at given pH after heating at 90 ◦C for 3 weeks are about 5 orders of magnitude lower than the solubility of amorphous zirconium hydroxide (Zr(OH)4(am)) kept at room temperature. Size distributions of the Zr colloidal species after heating were investigated by sequential filtration using different pore-sized membranes, and the contribution of the colloidal species to the solubility was assessed. The TEM images and XRD spectra of the solid phases after heating indicated the agglomeration and crystallization of the initial amorphous hydroxide solid phase. The solid phase was identified as crystalline oxide after heating at 90◦C. The solubility product determined from the solubility data excluding contributions of colloidal species is correlated to the particle size of the solid phase.