Beyond the silicate matrix: SQUID magnetometry and Raman spectroscopy reveal hidden hausmannite in sintered manganese ores

The depletion of high-grade manganese reserves necessitates the effective beneficiation of low-grade ferruginous manganese resources, which constitute the dominant share of Kazakhstan’s reserve base. This study investigates the structural and magnetic evolution of carbonate-rich Bogach and silicate-rich Zhaksy ores sintered between 600 °C and 1,200 °C. By integrating bulk elemental analysis with high-resolution Raman spectroscopy, Superconducting Quantum Interference Device magnetometry, and quantitative electron microscopy mapping, the research defines distinct phase transformation mechanisms. Results indicate that sintering at 1,000 °C triggers hausmannite nucleation in both ore types. In Bogach ore, carbonate decomposition facilitates phase segregation and the growth of large crystalline grains. Conversely, Zhaksy ore forms iron-substituted solid solutions where nanocrystalline hausmannite remains encapsulated within a stable silicate matrix. While these inclusions are invisible both to standard X-ray diffraction and to Raman spectroscopy, their presence is unambiguously established by a characteristic ferrimagnetic transition at 42 K. These microstructural differences dictate tailored beneficiation pathways: Bogach ore is amenable to high-intensity magnetic separation, whereas the silicate-matrix effect in Zhaksy ore requires either upstream removal of quartz ballast before sintering or a combination of ultra-fine comminution with high-gradient magnetic separation. These findings establish a notable correlation between thermal history and functional magnetic properties, providing a robust physical basis for industrial optimization.