Equilibrium precipitation and dissolution of iron cyanide solids in water

Iron cyanide solids are complex coordination compounds that are produced an d used in various commercial products and processes as well as clinical pro ducts. These solids are also present in spent potlining wastes associated w ith aluminum production sites and in areas of former manufactured gas plant (MGP) facilities as a result of disposal of cyanide-bearing materials in s oils containing iron. In such cases, the concentration of cyanide in ground water is governed by dissolution of the iron cyanide solids under various e nvironmental conditions. Understanding of the precipitation and dissolution chemistry of iron cyanide solids is still in a nascent state, however. In this work, the equilibrium solubility behavior of iron cyanide solids was s tudied as a function of PH, pE, and other solution conditions, including th ose conducive to coprecipitation of iron cyanide solids and hydrous ferric oxide. Equilibrium solubility products were determined for reagent-grade Pr ussian Blue, and for synthesized Prussian Blue and Turnbull's Blue. Prussia n Blue [Fe-4(Fe(CN)(6))(3)(s)] was shown to be the stable iron cyanide soli d at higher pE conditions over the aqueous pE-pH range, while Turnbull's Bl ue [Fe-3(Fe(CN)(6))(2)(s)] was identified as the stable iron cyanide solid at lower pE values. X-ray diffraction studies yielded the same crystalline structure for these iron cyanide solids. The Fe2+/Fe3+ ratios and, implicit ly, the chemical compositions of the solids, were determined using Mossbaue r spectroscopy. When the iron cyanide solids were precipitated in the prese nce of excess dissolved iron, a coprecipitate with hydrous ferric oxide app eared to form. The resulting solids exhibited equilibrium solubility higher than those of the pure-phase iron cyanides. The observed solubility behavi or in these cases could be described by considering the formation of a soli d solution.