The reduction of chromate ions by Fe(II) layered hydroxides

The reduction of chromate ions by Fe(OH)(2) and the iron (II)-iron (III) hy droxysulphate green rust, GR(SO42-), was studied to evaluate whether such s ynthetic layered hydroxides and the corresponding natural green rust minera l could be involved in the natural attenuation of contaminated environments . The resulting Cr (III) bearing phases, which would govern the subsequent behaviour of chromium, were clearly characterised. Both compounds proved to be very reactive and oxidised instantaneously while chromate ions were red uced to Cr (III) as evidenced by X-ray photoelectron spectroscopy. Mass bal ance (ICP-AES) demonstrated that the Fe/Cr ratio inside the solid end produ ct was equal to the initial Fe/Cr ratio. The solid phases, analysed by X-ra y diffraction, Raman and Mossbauer spectroscopies were identified as Cr-sub stituted poorly crystallised iron (III) oxyhydroxides in both cases, more p recisely delta-FeOOH when starting with Fe(OH)(2) and ferrihydrite when sta rting with GR(SO42-).