Aqueous Chemistry of Zirconium(IV) in Carbonate Media

The interactions between carbonate ions and zirconium oxychloride are studied by potentiometry, dialysis, and ¹³C‐ and ¹⁷O‐NMR spectroscopy in aqueous media. The nature of the soluble carbonatohydroxo complexes depends on the proportions of hydrogencarbonate and carbonate ions in solution before the addition of zirconium oxychloride. Carbonate media lead to polynuclear entities containing no more than two complexed carbonate ions per Zr⁴⁺. The presence of hydrogencarbonate favors the formation of less condensed and more carbonated complexes such as [Zr(CO₃)₄]⁴⁻. The polycondensation degree of the species decreases when the number of carbonates linked per Zr⁴⁺ increases. In all complexes, the carbonate is bidentate, and the metal atoms are linked via hydroxo bridges. The complexation of carbonate with Zr⁴⁺ occurs for a total carbonate concentration higher than 0.1M . Consequently, in natural medium, the speciation of this metal is governed only by the formation of hydroxo complexes.