Crystallization of metal fluoride hydrates from mixed hydrofluoric and nitric acid solutions, Part I, Iron (III) and Chromium (III)

Crystallization from hydrofluoric acid/nitric acid solutions supersaturated with Fe(III) and Cr(III) has been investigated. Iron and chromium crystallizes into a solid solution in the form of Cr(Fe)F₃·3H₂O, which is isostructural with CrF₃·3H₂O and α-FeF₃·3H₂O. By seeded isothermal desupersaturation experiments, the growth rate of β-FeF₃· 3H₂O crystals at 50 °C has been studied in hydrofluoric acid and nitric acid solutions containing Cr(III). It is found that the growth rate of β-FeF₃·3H₂O is essentially uninfluenced by the presence of 5 g/kg Cr(III). At 50 °C and a supersaturation ratio of 2 (c(FeF₃)_free/c_s(FeF₃) _free), the growth rate is (0.82.2)×10^-11 m/s in 3 mol/(kg solution) HF_free and 3 mol/(kg solution) HNO₃.