Heat Capacities of Concentrated Aqueous Alkaline Aluminate Solutions at 25 °C

Abstract

Heat capacities of aqueous NaOH/NaAl(OH) 4 solutions at total stoichiometric ionic strengths of up to 6 mol kg -1 and with up to 60 mol % substitution of OHby Al(OH) 4have been measured at 25 °C using a Picker flow calorimeter. The mean apparent molar heat capacities (C pφ ) of the NaOH/NaAl(OH) 4 mixtures were linear with respect to Al(OH) 4substitution, consistent with Young's rule. This enabled C pφ values to be derived for the hypothetical pure NaAl(OH) 4 (aq) solutions. The results so obtained are well described by a Pitzer model adapted from the literature, even up to high concentrations.

Heat capacities of aqueous sodium hydroxide/aluminate mixtures and prediction of the solubility constant of boehmite up to 300°C

“…On the other hand, Figure 5 shows that there is a broad consistency between the present data at 10 MPa and the earlier investigations at low temperatures and atmospheric pressure (Hovey et al, 1988;Magalhães et al, 2002), where the compressibility of aqueous electrolyte solutions is typically small.…”

“…(Hovey et al, 1988;Magalhães et al, 2002). Hemingway et al (1991) b Verdes et al (1992) c Takahashi et al (1973) d e f Wesolowski (1992) g Hovey et al (1988) Hovey et al, 1988;, Magalhães et al, 2002). Values for C pφ (NaOH, T) included for comparison (dotted lines).…”

“…In the fit of ion C p º(T) to Eq. (12), values measured at low temperatures and atmospheric pressure (Hovey et al, 1988;Magalhães et al, 2002) were combined with the present data given by Eq. (10).…”

Solubility and related properties in hydrometallurgy

“…The model is primarily based on experimentally determined densities and heat capacities [2][3][4][5][6], which are integrated to give Gibbs energies. From these, a Gibbs energy minimization algorithm calculates, in a thermodynamically consistent manner, enthalpies, and the activity and osmotic coefficients of these solutions as well as the solubilities of relevant solid phases, including gibbsite (Al(OH) 3 ), boehmite (AlOOH), and the "impurities" sodium oxalate and kogarkoite (Na 3 FSO 4 ) [7], in Bayer liquors over concentration and temperature ranges of industrial interest.…”

Solubility equilibria. From data optimization to process simulation

“…• osmotic coefficients and water activities; • relative apparent molar enthalpies, enthalpies of dilution [3,7]; • (apparent molar) heat capacities [9,10]; and • densities and (apparent) molar volumes [3,9].…”