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Representation of Excess Properties and Liquid Composition of Aqueous Solutions of the HF+Water System

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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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Authors and Affiliations

  1. Mohamed V University, Agdal-Rabat, Morocco

    Brahim Messnaoui

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  1. Brahim Messnaoui
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Correspondence to Brahim Messnaoui.

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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

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