Triborate Formation Constants and Polyborate Speciation under Hydrothermal Conditions by Raman Spectroscopy using a Titanium/Sapphire Flow Cell

Abstract

Solvent-corrected reduced isotropic Raman spectra of aqueous boric acid + sodium borate solutions have been obtained from perpendicular and parallel polarization measurements in a novel custom-made titanium flow cell with sapphire windows over the temperature range 25 to 300 °C at 20 MPa using the perchlorate anion, ClO4 –, as an internal standard. The reduced isotropic spectra of solutions yielded the first reported quantitative speciation results for polyborate ions in equilibrium with boric acid and borate in high-temperature aqueous solutions above 200 °C. The spectra obtained from solutions at low sodium/boron ratios, 0 < m Na ST/m B ST < 0.254, displayed well-defined bands at 880, 747, 615, and 532 cm−1, corresponding to the species B­(OH)3 > [B­(OH)4]− > [B3O3(OH)4]− ≫ [B5O6(OH)4]−, respectively. The triborate ion, [B3O3(OH)4]−, was found to be the major polyborate species in these boric acid-rich solutions in the range 25 to 300 °C. Thermodynamic formation constants for the triborate species, [B3O3(OH)4]−, calculated from the peak areas, are in agreement with the literature values reported by Mesmer et al at 50, 100, and 200 °C to within the combined experimental uncertainties. At 300 °C, the value for the formation constant, log K 31,m b = 2.259 ± 0.060, is larger than the value extrapolated from the results of Mesmer et al. by a factor of ∼3.

Boron Removal by Sorption on Modified Chitosan Hydrogel Beads

“…The broad absorptions in the regions 1150-1350 cm −1 were regarded as evidence for borates. The small bands at 477 and 567 cm −1 possibly suggested the presence of some polyborate species, such as [B5O6(OH)4] − [39]. , respectively.…”

Second Dissociation Constant of Carbonic Acid in H2O and D2O from 150 to 325 °C at p = 21 MPa Using Raman Spectroscopy and a Sapphire-Windowed Flow Cell

“…The flow cell, in its glycol-cooled containment box, was placed on a machined Teflon mount beneath the confocal microscope of the custom-made Horiba Jobin Yvon LabRam HR800 Raman spectrometer used in our previous work. , The Raman signal was collected in a 180° backscattering geometry using an Olympus EX41 confocal microprobe. The exciting laser was a 532 nm 250 mW Torus-200 diode-pumped solid-state (DPSS) laser.…”

“…The isotropic spectrum, I iso , which is defined by the theoretical formula is preferred for quantitative speciation studies because it contains only the symmetric vibrational modes and the baseline is very flat. In this study, the theoretical factor of 4/3, which applies to all scattering geometries, was replaced by the value 1.167 ± 0.001 for the optics of our instrument, based on calibration with standard solutions of carbon tetrachloride. , …”

“…Light and heavy water have distinct hydrogen-bonded structures, solvation behaviors, and physical properties due to differences in the zero-point energy of their bonds, and other effects. , The different ionic hydration effects between the two isotopic forms of water at high temperatures and pressures are not well-understood, and thermochemical data for deuterium isotopes effects above ∼70 °C are sparse. − The reason for the lack of experimental data is that the instrumentation required for quantitative measurements under hydrothermal conditions is highly specialized, ,− and large quantities of isotopically pure heavy water can be difficult to obtain. Although theoretical studies to predict high-temperature deuterium isotope effects from light water data have been attempted, accurate experimental thermodynamic and transport-property data in heavy water are required to test and develop these models.…”

“…The measurements were carried out in light and heavy water using a newly developed titanium flow cell with sapphire windows 9 capable of operating with basic solutions at temperatures up to 325 °C and at constant pressures up to 25 MPa, over extended periods of time. The flow cell and injection system were designed to minimize the effects of systematic errors by allowing the spectra of nearly identical solutions in light and in heavy water to be measured in sequence without having to change the optical geometry, temperature, or pressure.…”