From pig iron to simple and rare-earth doped spinel ferrites: an easily scalable method to obtain products with high added value and improved properties

Abstract

Spinel ferrites with the formula MFe2O4 [M= Co (cobalt), Cu (copper), Ni (nickel), or mixtures of Ni with Zn (zinc) and Gd (gadolinium)] were successfully synthesized using pig iron, an abundant raw material, and high-energy ball milling, a method commonly employed in the iron and steel industry. The addition of cellulose, sodium chloride, or citric acid as additives during milling enabled the modification of the microstructure of the resulting ferrites. Both simple and doped ferrites show the characteristic cubic spinel-type structure, with crystallite sizes ranging from 9 to 220 nm depending on the experimental conditions of synthesis. The elemental composition of the powders corresponds to the expected formula, homogeneously distributed, and silicon traces (Si < 0.5 at%). The magnetic behavior of all ferrites is ferrimagnetic; Cu, Ni, and NiZnGd ferrites show a “S” like hysteresis loop while CoFe2O4 exhibits a hysteresis loop more open. The values of saturation and coercivity of each ferrite are in well agreement with those reported for ferrites obtained by methods that allow to achieve thermodynamic equilibrium. NiZnGd-ferrites shows a good performance for both ORR and OER catalysis, with EJ10 (OER) and E1/2 (ORR) potentials of 1.7282 and 0.6485 V (vs. RHE), respectively, making it a strong candidate for use as an air cathode in Zn–air batteries and related energy conversion and storage technologies. Additionally, Ni and NiZnGd-ferrites show to be useful to remove more than 70.4 and 36.6% of lead and cadmium, respectively, from aqueous solutions, while also being easily separable and reusable.

Keywords: Spinel ferrites; ORR and OER catalysis; Heavy metals removal