Determination of the HCl dissociation constant at a temperature of 350°C and 200 bars of pressure by the potentiometric method using a ceramic electrode

Abstract

A technique has been developed for pH measurement in flow-through cells at temperatures from 175 to 350 ° C and pressures up to 350 bars in a nonisothermal cell consisting of a ZrO 2 (Y 2 O 3 ) ceramic electrode and a Ag/AgCl (2 M KCl, 25 ° C) flow-through reference electrode. This technique has been applied to determination of the HCl dissociation constant at 350 ° C and 200 bars; previously, the HCl dissociation has not been studied sufficiently reliably under these conditions. The obtained value p K dis = 2.16 ± 0.03 was used to estimate the acidity of fluids from their chemical composition at the vent of high-temperature submarine hydrothermal solutions.

Internally consistent thermodynamic data for aqueous species in the system Na–K–Al–Si–O–H–Cl

“…The data that were derived by Tagirov et al (1997) represent virtually all the experimental data available at the time when the evaluation was performed (e.g., Frantz and Marshall, 1984;Ruaya and Seward, 1987;Simonson et al, 1990;Sverjensky et al, 1991;Sretenskaya, 1992;Tagirov et al, 1997), except the experimental data points from Frantz and Marshall (1984) in the low-density region. Furthermore, the data from Tagirov et al (1997) are in excellent agreement with recent potentiometric measurements by Reukov and Zotov (2006) and reasonably consistent with the new conductance measurements by Ho et al (2001). Note that most of the experiments by Ho et al (2001) were performed in the low-density region (350-400 °C, 0.26-0.31 kbar) where calculations using the revised HKF model are not accurate.…”

H3O+Cl- Pair Association in Steam and Highly Compressible Aqueous Environments

“…Despite this wealth of experimental data, there is a persistent lack of agreement on the actual values of the association constant of aqueous HCl at near-critical conditions, and consequently, no consensus among experimentalists on the causes underlying that disagreement. For example, association constants determined from solubility data 19,21,22 appear to be at odds with those from conductance measurements, ,,, while those from potentiometric measurements by Reokov et al are neither consistent with similar measurements by Lvov et al nor consistent with the conductance-based modeling by Pokrovskii and Pokrovskii 25 have discussed in some details the potential sources for the observed disagreement, these discrepancies actually highlight the fact that the determination of the association constant is at best indirect, that is, it typically involves a series of difficult measurements, a fair amount of data interpretation and regression, as well as the involvement of conjectured approximations in the thermodynamic modeling. − Among those approximations, the recurrent use of “fully electrostatic” (primitive) models to regress the ion-pair association constants and interpret their behavior, such as Fuoss and Bjerrum approaches, might become a serious liability when considering the profound inhomogeneities exhibited by the water around the ions at these extreme conditions …”

“…Hydrochloric acid is an ubiquitous component in hydrothermal fluids and a key player in the dissolution, transport, and deposition of metal chlorides in HCl-bearing volcanic vapors, ore deposits, hydrothermal vents, , steam power generators, , and supercritical water oxidation reactors. , Its relevance is clearly highlighted by the large body of experimental data on the dissociation behavior of HCl accumulated over the years, involving electrical conductance, − calorimetric techniques, potentiometric, , and solubility measurements. − …”