Influence of copper ions on the precipitation of goethite and hematite in highly alkaline media

The effects of Cu-dopant on the precipitation of α-FeOOH and α-Fe2O3 particles in highly alkaline media were investigated using 57Fe Mössbauer and Fourier transform infrared (FT-IR) spectroscopies and thermal field emission scanning electron microscopy (FE SEM). Only α-(Fe, Cu)OOH solid solutions were obtained between r = 0.0099 and 0.0291, where r = [Cu]/([Cu] + [Fe]). A mixture of α-(Fe, Cu)OOH and α-(Fe, Cu)2O3 solid solutions was obtained between r = 0.0385 and 0.0566, whereas only an α-(Fe, Cu)2O3 solid solution was obtained between r = 0.0698 and 0.1666. Cu-substitutions in α-(Fe, Cu)OOH and α-(Fe, Cu)2O3 decreased the hyperfine magnetic field 〈Bhf〉 values. With increased Cu-substitution in an α-FeOOH type structure the IR shifts were observed. With an increased r value of initial solution a gradual elongation of α-(Fe, Cu)OOH particles along the crystallographic c-axis was observed. At r = 0.0476, some α-(Fe, Cu)OOH particles were ∼700 nm long, and correspondingly the width and thickness of these particles decreased markedly. With a further increase in r the length of α-(Fe, Cu)OOH particles decreased. α-(Fe, Cu)2O3 particles showed varying sizes in dependence on the precipitation conditions, whereas their geometrical shapes matched those typical of α-Fe2O3.