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

Abstract

Green rust (GR) consisting both of Fe(II) and Fe(III) was formed in an aqueous solution with a relatively low electrochemical potential. In order to understand both the reduction and oxidation reactions of copper in a GR suspension, the aqueous solution containing Green Rust 2(SO4 2� ) (GR2(SO4 2� )) was mixed with a copper sulfate solution and it was subsequently oxidized by passing a gas containing oxygen at room temperature. X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy were used for characterizing the reaction products. Copper ions were found to be reduced to metallic copper in the GR2(SO4 2� ) suspension, while a part of GR2(SO4 2� ) was oxidized to be transformed to � -FeOOH. The pH and oxidation-reduction potential values of the aqueous solution were measured during the reactions. The importance of the reduction of Cu(II) to metallic copper occurred in the GR2(SO4 2� ) suspension, and the oxidation processes of the suspension containing metallic copper was suggested as distinct reaction stages. These reaction stages are considered to be attributed to the different electrochemical potential of Cu(II)/Cu(0) and Fe(III)/Fe(II) in solution. [doi:10.2320/matertrans.MAW200818]