Thermodynamic modeling of ammoniacal nickel sulphate solutions

Abstract

The aim of this study was to build a thermodynamic model to extrapolate the system NiSO4–(NH4)2SO4–NH3–H2O which exists in aqueous hydrogen reduction processes of nickel. These solutions are relatively concentrated, and the temperature for solution preparation and reduction stages might range from room temperature up to 180–200°C. Temperature has a great effect on solution equilibria and the equilibrium solubility of simple and complex crystalline salts such as sulphates and hydroxides known to exist in the system. In this work, the role of kinetics is recognized, but only equilibrium phenomena reconsidered. The main focus of the study was on the modeling of salt solubility. In cases of a process solution where the precipitation of solid crystalline salts is highly undesirable it is important to know the safe limits for a ‘clear solution’ to operate even if the kinetics are unfavorable. Relatively concentrated solutions are strongly non‐ideal and realistic calculations on solution equilibria necessitate the modeling of excess thermodynamic properties of these solutions. The excess model selected for aqueous species was Pitzer's ion‐interaction model and for the gas phase Tsonopoulos' model. Emphasis in data assessment was on the thermodynamic modeling of various binaries and ternaries to create a substantial database for the approximation of the quaternary system.

Separation and concentration of cobalt from ammoniacal solutions containing cobalt and nickel by emulsion liquid membranes using 5,7-dibromo-8-hydroxyquinoline (DBHQ)

“…Furthermore, the ammonium ions form the cobalt ammine complex with the cobalt ions in the feed solution thereby decreasing the extent of extraction at these pH values, as also explained by Alguacil and Cobo [26]. This is also confirmed elsewhere [27]. Moreover, this decrease can be also explained with increasing solubility of extractant DBHQ in the aqueous feed solution at these pH values.…”

Kinetic modelling of nickel powder precipitation by high-pressure hydrogen reduction

“…Reaction kinetics have been studied by use of experimental precipitation studies (Li, 1992;Zhang and Lewis, 2006) and electrochemical experimental and modelling studies (Sobol, 1993;Osseo-Asare, 2003). Thermodynamic modelling of ammoniacal nickel sulphate solutions has been used to predict the operational region where precipitation of crystalline salts, which is highly undesirable, is not thermodynamically feasible (Kolhinen and Jalkanen, 2005). The effect of impurities namely, iron inherently present in leach solutions as ferrous sulphate and a morphology modifier (a polyacrylic acid derivative) widely used as an additive has also been investigated Lewis, 2006, 2007).…”