Thermodynamic interpretation of zirconium solubility in the presence of hydroxyacetic, 3-hydroxypropionic, and 2,3-dihydroxypropanoic acids

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The solubility of zirconium hydroxide in the presence of hydroxyacetic (glycolic, O20), 3-hydroxypropionic (O21), and 2,3-dihydroxypropanoic (glyceric, O201) acids was investigated as a function of pH_c = −log [H⁺] = 7−13 and total hydroxycarboxylic acid concentrations, [L]_tot = 10⁻⁴−10⁻¹ mol/dm³. The Zr solubility dependences on pH_c and [L]_tot indicated that ternary Zr(OH)₄(L)₂²⁻ complexes were the dominant soluble species under the experimental conditions. The formation constants of the Zr(OH)₄(L)₂²⁻ complexes were determined by least square fitting analysis of the solubility data and compared to the values for zirconium-poly(hydroxy)carboxylate analogs to elucidate the complexation mechanism of Zr-hydroxycarboxylates.