Formation of goethite and hematite from neodymium-containing ferrihydrite suspensions

The effects of neodymium (Nd) on the transformation of ferrihydrite to iron oxides was studied. The possible isomorphous substitution of Nd3+ for Fe3 in iron oxides was examined also. Nd was used as an inactive substitute of trivalent radioactive actinide elements. Hydrolysis of ferric nitrate solu tion containing 0-30 mole % of Nd formed Nd, Fe-rich ferrihydrite as initia l precipitates, which were poorly crystalline. Aging of the Nd-containing f irrihydrite in 0.3 M OH- at 30 degrees C and at pH 9.2 at 70 degrees C form ed Nd-free goethite and Nd-substituted hematite. The abundance of these cry stalline phases was related to Nd in the parent solutions. Phase abundance. unit-cell parameters, and peak width were estimated by use of the Rietveld method.