Characteristic Behavior of Nickel Ions during Transformation of Green Rust to Ferric Oxyhydroxides in Aqueous Solution

Abstract

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(SO 4 2À ) (GR2). GR2(SO 4 2À ) was synthesized from the solution of ferric and ferrous sulfate and that of sodium hydroxide. The suspension containing GR2(SO 4 2À ) with and without nickel was oxidized by passing oxygen gas into the aqueous solution, in which GR2(SO 4 2À ) was transformed into ferric oxyhydroxides. The pH and oxidation reduction potential (ORP) values of the aqueous solution were monitored during the transformation of GR2(SO 4 2À ). In addition, the concentrations of iron and nickel in the solution during the transformation of GR2(SO 4 2À ) were analyzed by using inductively coupled plasma atomic emission spectroscopy. The reaction conditions of the GR2(SO 4 2À ) suspension were found to be strongly influenced by the addition of nickel. The reaction product goethite, which was transformed from GR2(SO 4 2À ), 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.

Reduction of Copper Ions in Green Rust Suspension and Oxidation of Green Rust Containing Metallic Copper

“…The diffraction peaks of these samples show that the particles consisted mainly of -FeOOH. Small diffraction peaks located at approximately 13 and 17 , which are assigned to Fe 3 O 4 , were also detected. Since the intensities of these peaks decrease with increasing amount of the copper sulfate ions, copper in the GR suspension reduces the formation of Fe 3 O 4 and the nucleation and growth of -FeOOH transformed from the GR suspension may be influenced by copper.…”

“…As the shape of the -FeOOH particles obtained from GR appear to be independent of the addition of copper, copper does not seem to affect the morphology of -FeOOH obtained from GR. Compared to the shape of particles obtained from GR with nickel ions, 13) the shape of particles obtained from GR with nickel ions are evidently different. These results indicate that the morphologies of the iron hydroxides are changed by the species of foreign elements.…”

“…Such tendency was also observed in the case of GR added with nickel sulfate ions. 13) The increase of the oxidation rate of the GR suspension by copper may be caused by excess sulfate ions in copper sulfate, which may induce the dissolution of GR.…”

“…We have succeeded at synthesizing GR2(SO 4 2À ) by using chemical method and characterize the transformation process of GR2(SO 4 2À ) into the iron oxyhydroxides and oxides by aerial oxidation. [10][11][12][13] The results show that the transformation of GR2(SO 4 2À ) into the iron oxyhydroxides and oxides is sensitive to oxidation conditions such as reaction temperature, oxidation rate and existence of foreign elements.…”

“…6,7) Since GR is stable in an aqueous solution of relatively low potential, it is transformed into the iron oxyhydroxides and oxides through the dissolution and precipitation of Fe(II) and Fe(III) ions in an aqueous solution by oxygen gas in air. [8][9][10][11][12][13] Therefore, it is important to elucidate the influence of the addition of an alloying element on the transformation of the iron oxyhydroxides and oxides from the GR in an aqueous solution, in order to understand a role of the element on the transformation of the corrosion products. We have succeeded at synthesizing GR2(SO 4 2À ) by using chemical method and characterize the transformation process of GR2(SO 4 2À ) into the iron oxyhydroxides and oxides by aerial oxidation.…”