Comparative Study of Sodium Phosphate and Sodium Sulfate in Aqueous Solutions at (298.15 to 353.15) K

Abstract

The binary and ternary aqueous solutions of sodium phosphate or/and sulfate were studied using the hygrometric method from dilution to saturation in the temperature range from (298.15 to 353.15) K. The hygrometric measurements of the binary systems were combined with reference pure water, Na 3 PO 4 (s), and Na 2 SO 4 (s) solubility data to construct a chemical model that calculates solute and solvent activities from dilute to saturated solution concentration (for (Na 3 PO 4 (s)) up to m max = 9.00 mol·kg −1 at 353.15 K; and up to m max (Na 2 SO 4 (s)) = 3.40 mol·kg −1 at 313.15 K). The constructed model was also used to calculate thermodynamic solubility product (K°s p ) of Na 3 PO 4 (s) and Na 2 SO 4 (s) in the temperature range (298.15 to 353.15) K. The excess Gibbs energies of Na 3 PO 4 (aq) and Na 2 SO 4 (aq) were evaluated at various temperatures. The results for these aqueous solutions were influenced by the effect of hydration shell, with ion association or formation ion pairing. The anion solute PO 4 or SO 4 influences the hydration in an aqueous solution; indeed the hydrogen bonding of water in the hydration shells of PO 4 3− anion is preeminent over that of SO 4 2− . The mixed electrolyte solutions {(yNa 3 PO 4 + (1 − y)Na 2 SO 4 }(aq) were also investigated in the temperature range from (298.15 to 353.15) K and at total molalities from dilution (0.10 mol·kg −1 ) to saturation for different ionic-strength fractions (y) of Na 3 PO 4 with y = 0.20, 0.50, and 0.80. The water activity of mixed salts solutions and related properties such as osmotic and activity coefficients were carried out at various temperatures. The osmotic coefficients data were used to evaluate the mixing parameters of the ion interaction model θ MN and ψ MNX in the ternary system Na 3 PO 4 + Na 2 SO 4 + H 2 O.

Ab Initio Molecular Dynamics Simulation of the Phosphate Ion in Water: Insights into Solvation Shell Structure, Dynamics, and Kosmotropic Activity

“…In fact, the phosphate ion has been termed the choice of nature because of the ubiquitous presence of its derivatives in biomolecules. Therefore, with water being the biological solvent, it is not surprising that aqueous solutions of salts or molecules containing phosphate or hydroxyphosphate anions have been the subject of numerous scientific studies in the literature. − For example, Buchner and co-workers investigated phosphate salts in water using dielectric relaxation spectroscopy (DRS) and found the presence of slow and irrotationally bound water depending upon the concentration of the ion. A Raman spectroscopy with multivariate curve resolution (Raman-MCR) based study of aqueous solutions of sodium phosphate was carried out to understand the effects of the PO 4 3– groups on the stretching frequency of the OD bonds of surrounding water .…”

Hexafluorosilicate Salts in Wet Phosphoric Acid Processes: Properties of X2SiF6–H2O with X = Na+, K+, or NH4+ in Aqueous Solutions at 353.15 K

“…The calculated mineral solubility m s(cal) was also evaluated on thermodynamic considerations based on the approach of the ion interaction model. ,,− In the saturated solutions, the solubility of a hydrated salt was calculated from the equilibrium constant of the hydrated salt and the activity coefficients of all the electrolytes.…”

“…The water activity was measured using the hygrometric method previously described in earlier works. , The apparatus used is based on the measurement of the water activity over an aqueous solution containing nonvolatile electrolytes. The apparatus was amended and adapted to elevated temperatures, for the measurements at temperature 353.15 K. The apparatus was maintained at a constant-temperature with the standard uncertainty of temperature u (T) = 0.1 K. The measurement of the droplet diameter was made by a microscope with an ocular equipped with a micrometric screw.…”

“…Knowledge of the properties of aqueous solutions of hexafluorosilicate salts is essential to understand the interaction of aqueous solutions with minerals encountered in phosphate industry . This paper is a continuation of our research in phosphate aqueous solutions. , The main objectives of this study are to determine the thermodynamic properties of hexafluorosilicate salts X 2 SiF 6 –H 2 O with X = Na + , K + , or NH 4 + in aqueous solutions at a temperature of 353.15 K. The measurements of the water activity were performed using the hygrometric method, and the related properties were determined from dilution to saturated solution for Na 2 SiF 6 (aq), K 2 SiF 6 (aq), and (NH 4 ) 2 SiF 6 (aq). The mineral solubility of these hexafluorosilicate salts in water was also examined at T = 353.15 K.…”

Dynamics of Water in the Solvation Shell of an Iodate Ion: A Born–Oppenheimer Molecular Dynamics Study

“…Studies involving the hydration of ions in bulk and at interfaces have formed an active area of research for many years. , There have been many experimental and theoretical investigations of the structure and dynamics of water around ions to infer details of ion hydration. − The critical roles played by the dynamics of ion solvation shells in a number of chemical processes such as ion transport through membranes, reactions in aqueous phases, and transport of ionic solutes in water have made it a subject of immense importance. The hydration of polyoxyanions in bulk water and at aqueous interfaces and also their surface propensities have been studied on numerous occasions. − The iodate (IO 3 – ) ion is a polyoxyanion with a pyramidal shape containing positively charged iodine (will be referred to as I) and negatively charged oxygen (will be referred to as OI) atoms. However, its behavior in water is different from that of closely related anions like the iodide ion .…”