A spectrophotometric study of erbium (III) speciation in chloride solutions at elevated temperatures

The speciation of erbium in chloride-bearing solutions was investigated spectrophotometrically at temperatures of 100 to 250 °C and a pressure of 100 bars. The hydrated ion, Er3+, is predominant at ambient temperature, but chloride complexes are dominant at elevated temperature. Formation constants were calculated for the following reactions:equation(β1)Er3+ + Cl− = ErCl2+equation(β2)Er3+ + 2  Cl− = ErCl2+The values obtained for the first formation constant (β1) were 0.88 ± 0.11, 1.59 ± 0.12, 2.34 ± 0.11, and 3.09 ± 0.14 at 100, 150, 200 and 250 °C, respectively. Values of the second formation constant could only be determined at 200 and 250 °C, and were 2.95 ± 0.34 and 4.12 ± 0.12, respectively.The values for the first formation constant (β1), are identical within experimental error to the values predicted by Haas et al. [Haas, J. R., Shock, E. L., and Sassani, D. C. (1995). Rare Earth Elements in hydrothermal systems: estimates of standard partial molal thermodynamic properties of aqueous complexes of the Rare Earth Elements at high pressures and temperatures. Geochim. Cosmochim. Acta, 59, 4329–50.], whereas the values for the second formation constant (β2) agree relatively well with those predicted by Haas et al. (1995) and determined experimentally by Gammons et al. [Gammons, C.H., Wood, S.A., and Li, Y. (2002). Complexation of the Rare Earth Elements with aqueous chloride at 200 °C and 300 °C and saturated water vapor pressure. Special Publication — The Geochemical Society, (Water–Rock Interactions, Ore Deposits, and Environmental Geochemistry), 191–207.].