Environmental mineralogy: spectroscopic studies on ferrous saponite and the reduction of hexavalent chromium

A green-coloured phyllosilicate occurring on the walls of amygdaloidal cavities and along fractures in the Deccan Flood basalts at Killari, Maharashtra, India, has been identified as iron-rich saponite with a chemical composition [Na<Subscript>0.60</Subscript> K<Subscript>0.40</Subscript> Ca<Subscript>0.47</Subscript>] {Mg<Subscript>2.05</Subscript>Fe<Subscript>3.95</Subscript>} (Si<Subscript>6.45</Subscript>Al<Subscript>1.55</Subscript>) O<Subscript>20</Subscript>(OH)<Subscript>4</Subscript>. In order to explore the possible application of this phyllosilicate for environmental management, we have carried out X-ray photon spectroscopic (XPS) and diffuse reflectance spectroscopic (DRS) measurements on the dichromate solutions, in both the untreated and treated form. The dichromate solution treated with the saponite samples show a remarkable capability not only to adsorb hexavalent chromium but also effect a reduction of hexavalent to trivalent chromium at an efficiency of 75%. These valence states of chromium were characterised unambiguously by XPS and DRS spectra collected at room temperature. Our studies show that Killari saponite is capable of reducing Cr (VI) to Cr (III). The ferrous saponite in Deccan Flood basalts could therefore be a useful mineral in environmental management in areas affected by Cr (VI) effluents. Copyright Springer Science+Business Media B.V. 2007