Recovery of manganese from a low-grade waste and valorization via the synthesis of a nanostructured magnetic manganese ferrite

Highlights: • Full recovery of Mn was obtained by preheating and leaching of a low-grade Mn waste. • The leachate was purified and enriched to prepare the synthesis precursor. • Different synthesis conditions were examined to obtain pure MnFe₂O₄ via DOE. • Nano- and micro-sized powders were formed through two different synthesis methods. • Both synthesized powders illustrate remarkable magnetic properties. This study aims at recovering manganese from a low-grade mining waste and valorizing it through the synthesis of manganese ferrite (MnFe₂O₄). Full recovery of manganese from the low-grade waste was obtained by heat treatment (700 °C), and leaching optimization of the waste in a reductively promoted sulfuric acid medium. Subsequently, the Fe: Mn molar ratio (2:1) of the leachate was adjusted to prepare the precursors for the MnFe₂O₄ synthesis through co-precipitation. The optimization of the synthesis parameters including temperature (15–90 °C), aging time (0–120 min), and calcination temperature (800–1200 °C) was investigated. The optimum condition suggested by the response surface method (RSM) led to the synthesis of pure plate-like MnFe₂O₄. Additionally, nano-sized particles (45 nm) were obtained at the 90 °C synthesis temperature, 120 min aging time, and without any calcination. Both nano-sized and plate-like MnFe₂O₄ particles with the saturation magnetization of 34.47 and 51.03 emu g⁻¹ presented superior magnetic properties.