Phase Formation and Solubilities in the Ternary System Ni(OH)2–NiCl2–H2O at 25 and 200 °C

Abstract

The solid/liquid equilibria in the ternary system Ni(OH)2–NiCl2–H2O at temperatures of 25 and 200 °C have been investigated by applying equilibration periods of up to 45 months (3 years and 9 months). The equilibration process was studied by isothermal saturation methods using different solids as starting materials. At 200 °C, Ni2Cl(OH)3 and NiCl(OH) occur as stable phases, whereas a solid solution, NiClx(OH)2–x (ss‐type‐OH), appears as an intermediate phase. At 25 °C, two nickel(II) chloride hydroxide hydrates, Ni3Cl2+x(OH)4–x·4H2O and Ni3Cl(OH)5·4H2O, are formed. The latter phase was characterized for the first time and a structural model was created from a Rietveld refinement of the powder X‐ray diffraction pattern. A systematic investigation of the solubilities at 25 °C revealed that Ni2Cl(OH)3 is the solid phase in both dilute and concentrated NiCl2 solutions at this temperature. In general, all stable and metastable phases in the system Ni(OH)2–NiCl2–H2O exhibit very low solubility, but during the very slow phase transformations high hydroxide supersaturations occur that are persistent for years.