A reliable procedure to predict salt precipitation in pure phases

Abstract

-This article proposes a new procedure to compute solid-liquid equilibrium in electrolyte systems that may form pure solid phases at a given temperature, pressure, and global composition. The procedure combines three sub-procedures: phase stability test, minimization of the Gibbs free energy with a stoichiometric formulation of the salt-forming reactions to compute phase splitting, and a phase elimination test. After the phase splitting calculation for a system configuration that has a certain number of phases, the phase stability test establishes whether including an additional phase will reduce the Gibbs free energy further. The criteria used for phase stability may lead, in some cases, to the premature inclusion of phases that should be absent from the final solution but, if this happens, the phase elimination sub-procedure removes them. It is possible to use the procedure with several excess Gibbs free energy models for liquid phase behavior. The procedure has proven to be reliable and fast and the results are in good agreement with literature data.

Processes for working-up an aqueous fluosilicic acid solution

“…The first method consisted of adding sodium chloride (NaCl) as it is more soluble in water than is sodium fluoride. 8,9 The second method includes the addition of ethanol into the solution as sodium fluoride is insoluble in alcohols. 10 The precipitate of sodium fluoride is separated by filtration of the suspension.…”