Characteristic behavior of nickel ions during transformation of green rust to ferric oxyhydroxides in aqueous solution

X-ray diffraction, transmission electron microscopy, and X-ray absorption spectroscopy were used for characterizing the role of nickel in the transformation of Green Rrust 2(SO42-) (GR2). GR2(SO42-) was synthesized from the solution of ferric and ferrous sulfate and that of sodium hydroxide. The suspension containing GR2(SO42-) with and without nickel was oxidized by passing oxygen gas into the aqueous solution, in which GR2(SO42-) was transformed into ferric oxyhydroxides. The pH and oxidation reduction potential (ORP) values of the aqueous solution were monitored during the transformation of GR2(SO42-). In addition, the concentrations of iron and nickel in the solution during the transformation of GR2(SO42-) were analyzed by using inductively coupled plasma atomic emission spectroscopy. The reaction conditions of the GR2(SO42-) suspension were found to be strongly influenced by the addition of nickel. The reaction product goethite, which was transformed from GR2(SO42-), also appeared to be stabilized by the addition of nickel. These results indicate that the species of the solid particles formed in the solution are controlled by the addition of foreign elements.