Effect of calcination temperature on Indian Ocean manganese nodules. Mossbauer, XRD, FT-IR and TG-DTA studies

The effect of calcination temperature on the physico-morphological properti es of Indian Ocean manganese nodules has been investigated. Mossbauer, XRD, FT-IR spectroscopic and TG-DTA studies on the manganese nodules gave some idea of the phase transformations in the temperature range 110-1000 degrees C. Mossbauer studies reveal that the iron in the untreated nodule is mainl y present as gamma-FeOOH along with minor amount of iron phosphate and/or s ilicate. No phase transformation has been observed in the calcined sample u p to 500 degrees C and beyond that gamma-FeOOH phase transforms to alpha-Fe 2O3 and delta-MnO2 to Mn2O3. A solid solution of Fe2O3 and Mn2O3 is formed above 700 degrees C and beyond that, some amount of Fe exists in magnesium manganese iron oxide form. Insertion of magnesium into the Mg-Mn ferrite st ructure becomes greater at greater than or equal to 900 degrees C. (C) 1999 Elsevier Science B.V. All rights reserved.