Graphical methods for representing form and stability of aqueous metal ions

The equilibrium distributions of solute species of aluminum at 25°C and one atmosphere pressure are shown graphically in systems containing fluoride, as functions of the total dissolved aluminum and fluoride. The predominant form of complex and degree of complexing are also shown graphically as functions of pH and fluoride activity. The graphs are based on the simultaneous solution of the equations representing nine complexing equilibria and three stoichiometric summarizations, using a fixed value of ionic strength equal to 0.1. Solubility relationships for aluminum hydroxide and cryolite also are shown graphically, using the same coordinates and additional equilibria. By overlaying an appropriate species distribution graph with a solubility graph a relatively complete summary of chemical relationships in an aqueous aluminum system can be obtained. Although this type of model has important limitations, it can accommodate enough variables simultaneously to have practical value and similar procedures could be used for other elements and systems of interest in low-temperature aqueous geochemistry.