Measurement and Modeling of the Solubility of NH₄VO₃ in the Na₂HPO₄–H₂O and (NH₄)₂HPO₄–H₂O Systems

Abstract

The solubilities of ammonium metavanadate (NH 4 VO 3 ) in (NH 4 ) 2 HPO 4 −H 2 O and Na 2 HPO 4 −H 2 O systems were measured in the temperature range from 298.15 to 338.15 K by the isothermal dissolution method. The experimental data indicate that the solubility of NH 4 VO 3 increases with the addition of Na 2 HPO 4 , while it first decreases and then increases with the addition of (NH 4 ) 2 HPO 4 . The common ion effect and chemical equilibrium were used to explain the solubility tendencies. Two models, the Bromley−Zemaitis model and Pitzer model, were selected to correlate the solubilities of NH 4 VO 3 in the above systems. The parameters of the new model referring to four ion−ion pairs and one ion−molecule pair were obtained via the regression of the experimental data, and the results agreed well with the experimental values. The new chemical model was then applied to analyze the main vanadium-bearing species distribution in the systems mentioned above. All of this work will develop the thermodynamics for an industrial application in the precipitation of NH 4 VO 3 .

A Closer Look into Solubility in the Binary NaVO3–H2O and NH4VO3–H2O Systems from 298.15 to 333.15 K and 0.1 MPa

“…Solubility of NH 4 VO 3 in water. Black squares, this work; blue circles, Gong et al; purple upward triangles, Trypuć and Kiełkowska; orange downward triangles, Trypuć and Drużyński; green diamonds, Yan et al; red stars, Liu et al; blue crosses, Meyer; blue rightward triangles, Andreev; yellow plus signs, Lachartre (the point at 369.15 K not shown); blue asterisk, Fedorov et al; pink square, Grigoreva and Belyaev; brown hexagram, Arkhipov and Kashina; solid line: fit of eq to all data. Blue dashed line: fit of eq to the present data.…”

“…Unfortunately, there is currently a lack of accurate data for the thermodynamic properties of aqueous vanadium solutions. Although considerable efforts have been made to determine the identity and the formation constants of the species existing in aqueous V­(V) solutions, these studies have been limited to low V concentrations (<0.3 mol/kg). − The experimental data available for concentrated solutions include mostly solubilities and densities for a number of binary, ternary, and quaternary systems containing NaVO 3 and/or NH 4 VO 3 as a component. − A notable portion of the above data comes from the works of Trypuć and co-workers − and most of the above publications report only a few experimental points for the binary systems. Also, it seems that the existence of two solid forms of NaVO 3 in the stability region of liquid water has practically been omitted in the more recent solubility studies although discovered already by McAdam and Pierle over a hundred years ago .…”