The aqueous geochemistry of Zr and the solubility of some Zr-bearing minerals Original Research Article

Literature data on the thermodynamics of complexation of Zr with inorganic species, at 25°C, have been critically reviewed. The preponderance of published complexation constants deal with F− and OH− ions. Stability constants for the complexation reactions are relatively independent of ionic strength and thus recomended values for each ligand type are averages of the most reliable data. Complexation constants under elevated conditions (T equal-or-less, slanted 250°C andPv = PH2O) have been predicted for various Zr complexes (F−, Cl−, SO42− and OH−) using Helgesonʹs electrostatic approach. Predominance diagrams (calculated for simple systems with these constants) suggest that, over a wide range of pH conditions, Zr(OH)4(aq) will dominate the aqueous geochemistry of Zr except under very high activities of competing ligands (e.g., F−, SO42−).