Raman Spectroscopy of Aqueous ZnSO_4 Solutions under Hydrothermal Conditions: Solubility, Hydrolysis, and Sulfate Ion Pairing

摘要

Raman spectra have been measured for aqueous ZnSO_4 solutions under hydrothermal conditions at steam saturation to 244 deg C; solubility has been recorded as a function of temperature from 25 to 256 deg C. The high-temperature Raman spectra contained two polarized bands, which suggest that a second sulfato complex, possibly bidentate, is formed in solution, in addition to the 1:1 zinc(II) sulfato complex, which is the only ion pair identified at lower temperatures. Under hydrothermal conditions it was possible to observe the hydrolysis of the zinc(II) aquo ion by measuring the relative intensity of bands due to SO~(2-)_4 and HSO~-_4 according to the equilibrium reaction [Zn(OH_2)_6]~(2+) + SO~(2-)_4 -> [Zn(OH_2)_5OH]~+ + HSO~-_4 The precipitate in equilibrium with the solution at 210 deg C could be characterized as ZnSO_4 centre dot H_2O (gunningite) by X-ray diffaction (XRD) and Raman and infrared spectroscopy. At 244 deg C the equilibrium precipitate could be identified as ZnSO_4 (zincosite).