Abstract
The electrolyte-NRTL model was used to describe the thermodynamic excess properties and the liquid composition of aqueous hydrofluoric acid solutions for overall HF concentrations ranging from dilute to a molality of 20 mol⋅kg−1. Within the framework of this model, three different mechanisms were tested. The first one considers only the dissociation of HF into H+ and F−. The second mechanism takes into account the dissociation of HF and the chemical reaction for formation of HF −2 . The third mechanism considers, in addition to these two chemical reactions, the reaction that leads to formation of the dimer H2F −3 . The experimental osmotic coefficients of the HF + H2O system were used to estimate the interaction parameters of this model. The resulting parameters yield an accurate description of the Gibbs-Duhem relation for the three mechanisms. The estimated liquid phase speciation for fluoride in the HF+H2O system is comparable to the experimental values of Braddy et al.
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Abbreviations
- a i :
-
activity of species i
- A φ :
-
Debye-Hückel constant
- f i :
-
mole fraction of activity coefficients
- G ji :
-
electrolyte-NRTL parameters
- G ji,ki :
-
electrolyte-NRTL parameters
- I x :
-
mole fraction ionic strength
- K :
-
chemical equilibrium constant on the molal scale
- m i :
-
molality of species i
- M s :
-
molecular weight of the solvent
- n :
-
mole number
- N :
-
number of experimental points
- p :
-
parameter number
- R :
-
gas constant
- T :
-
temperature
- x i :
-
liquid phase mole fraction of species i
- x ij :
-
effective local mole fraction of species i around the central species j
- z i :
-
absolute charge number of ionic species i
- γ i :
-
molal activity coefficient of species i
- φ :
-
osmotic coefficient
- ρ :
-
Electrolyte-NRTL parameter
- τ ji ,τji,ki:
-
interaction parameters
- α :
-
nonrandom factor
- cal:
-
calculated
- exp :
-
experimental
- ex:
-
excess
- lc:
-
local composition
- pdh:
-
Pitzer-Debye-Hückel
- ∞:
-
infinite dilution
- *:
-
unsymmetric
- a :
-
anion
- c :
-
cation
- i,j,k:
-
any species
- m :
-
molecule
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Messnaoui, B. Representation of Excess Properties and Liquid Composition of Aqueous Solutions of the HF+Water System. J Solution Chem 37, 715–726 (2008). https://doi.org/10.1007/s10953-008-9272-4
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DOI: https://doi.org/10.1007/s10953-008-9272-4