Hydrolysis and Complex Formation of Zr and Hf in Aqueous Solutions of HClO4, HCl, and NaOH in Equilibrium with Baddeleyite (Zr and Hf)O-2(cr) at 250 degrees C

摘要

The equilibrium concentrations of Zr and Hf in aqueous solutions of HClO4 {0.8-1.08 mol (kg H2O)-1}, HCl {0.1-1.05 mol (kg H2O)(-1)}, and NaOH {0.24-1.02 mol (kg H2O)(-1)} equilibrium with baddeleyite (Zr and Hf)O-2(cr) are determined according to solubility at 250 degrees C and the saturated vapor pressure of the solutions. It is found that hydroxo complexes Me(OH)(3)(+), Me(OH)(4)(0), Me(OH)(5)(-), and Me(OH)(6)(2-) are the main products of the hydrolysis of Zr and Hf. In solutions of HCl, the growth in the solubility in comparison with solutions of HClO4 is due to the formation of hydroxo chloride complexes Me(OH)(2)Cl-3(-), while for Hf, the reaction proceeds up to the formation of HfOHCl4-. The stability of the complexes of Hf is higher when compared to Zr. This is especially true for neutral complexes Me(OH)(4)(0), the stability of which differs by an order of magnitude, which can lead to the fractionation of these elements in the region of pH from weakly acidic to weakly alkaline. The thermodynamic properties of the complexes of Zr and Hf are determined.