Natural Manganese Ore as a Functional Additive in Calcium Aluminosilicate Glasses

We report the influence of manganese ore addition on the structural, thermal, optical, and magnetic properties of calcium aluminosilicate glasses synthesized using scheelite tailings as the main precursor, doped with different amounts of natural manganese ore (1-10 wt %). The samples were prepared by the melt-quenching method at 1400 °C in a graphite crucible followed by rapid cooling. The elemental composition confirmed the increase of Mn content with ore addition. X-ray diffraction revealed a broad diffuse scattering characteristic of an amorphous structure, confirming the formation of a glassy matrix. Transmission electron microscopy indicated the presence of amorphous nanoparticles or nanoclusters dispersed within the matrix, with more pronounced clustering at higher Mn concentrations. Infrared spectroscopy revealed structural modifications in the silicate network, including shifts in the Si-O-Si and Si-O-Al vibrational bands and the increase of nonbridging oxygen sites, suggesting that manganese promotes structural rearrangements and partial depolymerization of the glass network, consistent with a modifier-like behavior. Thermal analysis revealed glass transition temperatures between 781 and 809 °C and crystallization temperatures between 1032 and 1116 °C, indicating good thermal stability. The optical results show the transmittance and absorbance curves and the electronic transitions, explaining the color variation among the samples and providing the energy level for the electronic states using Racah parameters. The estimated band gap for the samples resulted in values between 1.75 and 2.05 eV, except for the least Mn-incorporated sample (not determined). The magnetic results show g-factors around 2.0, corresponding to Fe³⁺ and Mn²⁺ signals and an enlargement of the peak-to-peak line width (ΔH _pp ), indicating the presence of clusters or particles immersed in the glass matrix. Hysteresis measurements presented an increase in magnetization and coercivity with manganese ore increase, resulting from the Mn and Fe ions' interactions and the clusters formed inside the amorphous structure. These results demonstrate that manganese ore incorporation significantly influences the structure and the physical properties of calcium aluminosilicate glasses derived from mining tailings, highlighting their potential for technological applications.