The adsorption and catalytic transformations of chromium on Mn substituted goethite

Structural Incorporation of Manganese into Goethite and Its Enhancement of Pb(II) Adsorption

“…cations by substituting the iron. ,− The content of Al­(III) in natural goethite can be as high as 33% in molar ratios, while other elements are less than that. ,, By using Raman and Fourier transform infrared spectroscopy (FTIR) as well as microscopic techniques, the cation substitutions have been shown to alter the structure and surface reactivity of goethite to a certain extent, which further affects adsorption behavior of the heavy metals on it. , Among these cations, manganese is often substituted for Fe in many natural iron-bearing minerals, especially in goethite, due to its high affinity with Fe and almost equal radii of Fe ( r Fe3+ = r Mn3+ = 0.645 Å) . The incorporated Mn predominantly presents as Mn 3+ and/or Mn 4+ in an oxidizing environment. ,, Such incorporation normally alters the structure of goethite and its environmental performance. , Mn substitution observably enhances the oxidation of arsenite (As 3+ ) to arsenate (As 5+ ) by goethite, which suppresses the toxicity of arsenic in the environment . However, the valence of Mn on the goethite surface layer has not yet been accurately determined, which is crucial for understanding the surface reactivity.…”

“…13,19,22 Such incorporation normally alters the structure of goethite and its environmental performance. 31,25 Mn substitution observably enhances the oxidation of arsenite (As 3+ ) to arsenate (As 5+ ) by goethite, which suppresses the toxicity of arsenic in the environment. 32 However, the valence of Mn on the goethite surface layer has not yet been accurately determined, which is crucial for understanding the surface reactivity.…”

Sorption of Cr(VI) onto natural iron and aluminum (oxy)hydroxides: Effects of pH, ionic strength and initial concentration

“…Chromium is found in various oxidation stages ranging from −II to +VI. Cr(III) and Cr(VI) are of major environmental significance depending on pH and redox conditions [1,2]. In sediments, chromium can be present in two oxidation states [Cr(III) and Cr(VI)], trivalent chromium being an essential element in animal and human nutrition, and hexavalent chromium being toxic to organisms.…”

The role of Pb2+ ions doping in the mechanism of chromate adsorption by goethite

“…However, in most of the studies reported in the literature attention is given only to arsenate and arsenite and very little is known about the interaction of other important oxyanions like phosphate, sulphate, chromate, etc. It was only recently when Wu et al [18], reported adsorption of Cr (VI) on the Mn-substituted goethite and showed that chromate adsorption on goethite can be enhanced with Mn-doping due to increase in specific surface area. The present study is, therefore, aimed to investigate the impact of Pb-doping on the structure and surface properties of goethite and changes in its adsorption properties towards chromate at different pH and temperatures.…”