Synthesis of manganese ferrite from spent Zn–MnO2 batteries and its application as a catalyst in heterogeneous photo-Fenton processes

Abstract

The widespread use, serious environmental impacts, and high disposal costs of Zn–MnO2 batteries make their recycling attractive and necessary. In this study, manganese ferrite was synthesized by two routes: from commercial reagents (MnFe2O4-R) and from manganese recovered from the cathodes of spent Zn–MnO2 batteries (MnFe2O4-B). X-ray diffraction (XRD) and inductively coupled plasma optical emission spectrometry revealed that the cathode material contained MnO2, Mn3O4, manganese metal, and traces of zinc and lead. MnFe2O4-R and MnFe2O4-B were characterized by XRD, energy-dispersive X-ray spectroscopy, atomic absorption spectrometry, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). SEM and TEM showed that MnFe2O4-R and MnFe2O4-B were composed of irregularly shaped particle agglomerates of nanoscale dimensions and varied geometry. Manganese ferrites were evaluated as catalysts for the heterogeneous photo-Fenton degradation of methylene blue. MnFe2O4-R and MnFe2O4-B achieved 98 % and 92 % decolorization in 120 min of reaction, respectively. Analysis of decolorized dye solutions by ion chromatography showed the presence of formic and acetic acids. The reactions followed pseudo-first-order kinetics. This study presents a green method to produce photocatalytic materials that may find application in wastewater treatment.