Simulation of chemical phenomena in the Co(NO 3) 2–Na 2CO 3–H 2O system based on a thermodynamic model

Abstract

A simulation for the Co(NO 3) 2–Na 2CO 3–H 2O system based on a thermodynamic model was proposed which predicts possible equilibrium states attained among gas, aqueous and solid phases under isothermal and isobaric conditions. Various chemical species such as CoOH + the cobalt complex, carbonate species in aqueous solution, precipitate of basic cobalt carbonate and CO 2 gas were taken into account. By using the Debye–Hückel formula for the activity coefficients of ionic species, apparent equilibrium constants of chemical reactions were well evaluated. A thermodynamic model was constructed by combining mass action law, mass balance, and charge balance equations together with equilibrium conditions among different phases. Simulation was carried out to compute concentrations of various chemical species in aqueous solution, amount of precipitate, and pressure of CO 2. In order to examine the validity of the thermodynamic model, the computed pH values were compared with experimental results and a relatively good agreement between them was obtained.