Densities of NaOH(aq) at Temperatures from (323 to 573) K and 10 MPa Pressure

Abstract

Densities of sodium hydroxide solutions at concentrations of 0.1 j m/mol‚kg -1 j 8 have been measured by vibrating-tube densimetry over the temperature range 323 e T/K e 573 at a pressure of 10 MPa. The purposebuilt densimeter, which is capable of measuring densities of corrosive fluids at temperatures up to 573 K and pressures up to 30 MPa, has a platinum-rhodium vibrating tube with inlet/outlet tubes of platinum and an optical detection system. Calibrations were carried out with water and aqueous solutions of sodium chloride at temperatures up to 523 K. At higher temperatures, nitrogen was substituted as the auxiliary density reference because of uncertainties in the NaCl(aq) densities. The apparent molar volumes of NaOH(aq) calculated from the measured densities were fitted with an extended Redlich-Meyer equation. The present results are in good agreement with literature data but are more precise. The current global accuracy in the densities of NaOH(aq) appears to be about 0.1 %, being significantly better at lower concentrations and temperatures but slightly worse at higher concentrations and temperatures. More accurate knowledge of the densities of the reference materials (other than water) used for calibrating vibrating-tube densimeters under extreme conditions is probably required to improve the accuracy of such data.

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. The modeling software developed in our laboratory is known as BAYER.EXE [1].…”

“…A purpose-built vibrating-tube densimeter has been established in our laboratory, which has a platinumrhodium vibrating tube with inlet/outlet tubes of platinum and an optical detection system, and is capable of measuring densities of corrosive fluids at temperatures up to 300 °C and pressures up to 30 MPa [3]. Densities of sodium hydroxide solutions at concentrations 0.1 < m/mol kg −1 < 8 have been measured using this instrument over the temperature range from (50 to 300) °C at a pressure of 10 MPa [3].…”

“…Densities of sodium hydroxide solutions at concentrations 0.1 < m/mol kg −1 < 8 have been measured using this instrument over the temperature range from (50 to 300) °C at a pressure of 10 MPa [3]. The apparent molar volumes, V φ , of ternary, aqueous NaOH + "NaAl(OH) 4 " mixtures obey a linear pro-rata additivity rule as a function of aluminate substitution, also known as Young's rule (Figs.…”

“…The refining of alumina from bauxite ores, which are found in abundant deposits in Australia and elsewhere, occurs via the Bayer process. This hydrometallurgical process is employed worldwide and, in brief, involves a circuit of hot, concentrated, alkaline sodium aluminate solutions ("Bayer liquors") for the selective extraction ("digestion") of alumina and, on cooling, the subsequent precipitation of purified gibbsite, Al(OH) 3 . The Bayer process is often referred to as the largest recrystallization process in the world (in modern Bayer plants, ~500 million liters of caustic aluminate solution are in the circuit at any time).…”

Aqueous electrolyte solution modelling: Some limitations of the Pitzer equations

“…(3) is a single example). For instance, isothermal fits of φ C p and φ V for NaOH(aq) and its mixtures with NaAl(OH) 4 (aq), measured to T = 573.15 K at P = 10.0 MPa, have been performed recently (Hnedkovsky et al, 2007(Hnedkovsky et al, , 2010Schrödle et al, 2008Schrödle et al, , 2010. When these results were fitted to temperature functions, error propagation led to model uncertainties which significantly exceeded the experimental precision of the measured data.…”