A practical guide for determining the solubility of metal hydroxides and oxides in water

Abstract

Abstract In response to increasing metal toxicity concerns, new and more stringent regulations are driving industry to better understand the fate of metals in the environment. As a result, practicing engineers need a set of tools for quickly understanding the aqueous chemistry of the system at hand. This paper presents a practical guide for estimating the solubility of metal hydroxides/oxides in aqueous systems. Equilibrium chemistry software from OLI Systems, Inc. (Morris Plains, NJ) was used to predict the solubility of metal hydroxides/oxides in water as a function of pH. The product is an overall metal solubility diagram containing the solubility curves for 12 metal hydroxides/oxides. The curves are based on a commercially available thermodynamic database and were validated against literature solubility data. In most cases, the curves depict the solubility of the less stable crystalline or amorphous form of the metal hydroxide or oxide. This will be typical of industrial situations where aging of the solid phase is often minimal. The solubility curves are best viewed as “solubility bands” that can extend as much as an order of magnitude above and below the predicted lines. Two case studies illustrate the usefulness of the overall metal solubility diagram to practicing engineers.