AQUEOUS SPECIATION OF YTTRIUM AT TEMPERATURES FROM 25 TO 340-DEGREES-C AT P-SAT - AN IN-SITU EXAFS STUDY

The solvation environment of aqueous yttrium in chloride bearing solut ions was characterised by EXAFS spectroscopy at temperatures from 25 t o 340 degrees C. Four solution compositions were considered containing 0.1 M YCl3, 0.1 M YCl3 + 0.23 M HCl + 1.0 M NaCl, 0.1 M YCl3 + 0.23 M HCl + 2.0 M NaCl, and 0.05 M Y(NO3)(3), respectively. Yttrium was fou nd to be surrounded by an inner coordination shell of H2O, the coordin ation number decreasing from 9-10 to similar to 8 with increasing temp erature from 25 to 340 degrees C. The Y-O interatomic distance is cons tant 2.37 +/- 0.02 Angstrom at temperatures up to 340 degrees C. Yttri um chloride inner sphere complexing is negligible up to 340 degrees C for all solutions, including that containing 2.5 M chloride. This obse rvation implies that chloride inner sphere complexes play an insignifi cant role in the solubility and transport of yttrium, and by analogy t he heavy rare-earth elements in sub critical crustal fluids. Data anal ysis of EXAFS spectra of the 0.1 M YCl3 solution at temperatures in ex cess of 250 degrees C indicate the presence of yttrium atoms located a t similar to 3.6 Angstrom and similar to 4.9 Angstrom from the central yttrium atom. This latter observation is consistent with yttrium poly atomic species formation, or polymerisation. (C) 1998 Elsevier Science B.V. All rights reserved.