THERMODYNAMIC STABILITY OF ZIRCONIUM(IV) COMPLEXES WITH HYDROXY IONS

A protometric study on the speciation of zirconium(IV) was performed i n an aqueous solution at 25 degrees C in KNO3 and four ionic strengths (0.2, 0.5, 1, and 2 mol.dm(-3)). This study indicates the formation o f the soluble species Zr(OH)(3)(+), Zr-2(OH)(7)(+), and Zr(OH)(4) in t he pH range 1.5-3.5. The use of an appropriate titration technique all ows the precipitation of the zirconium hydroxide to be Limited. The ov erall stability constants beta(mlh) of these three hydroxo complexes w ere computed and refined, by the program PROTAF, for each ionic streng th. The solubility product Ks of Zr(OH), was calculated by taking thes e beta(mlh) constants into account. The thermodynamic values were dete rmined by extrapolation at zero ionic strength (Specific ion Interacti on Theory method): log beta degrees(10-3) = -0.52 (0.01); log beta deg rees(20-7) = -2.22(0.07); log beta degrees(10-4) = -4.52 (0.07); logKs degrees = -55.26(0.08).