Enhancing the eco-friendly use of manganese sulfate residue via recognition and reconstruction of metastable structure

Abstract

Long-term accumulation of manganese sulfate residue can lead to the release of soluble manganese ions, which in turn can contaminate the surrounding environment. However, effectively guiding the treatment of soluble manganese in manganese sulfate residue is challenging due to limited understanding of its metastable structure. In this study, the metastable phase of manganese sulfate residue was analyzed by transmission electron microscope (TEM), cross-reaction X-ray energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD). The results reveal that the metastable phase within manganese sulfate residue consists of amorphous hydroxide and calcium sulfate. Furthermore, the amorphous hydroxide colloid is coated by calcium sulfate. The reconstruction of the metastable structural phase in manganese sulfate residue was achieved by adding BaCO3. The toxic leaching of the residue after phase reconstruction was assessed. The results show that the lowest leaching concentration of Mn and Ba were 0.6737 mg L−1 and 1.778 mg L−1, respectively. The leaching amounts of Mn and Ba were within the allowable range of GB 8978–1996 and GB 5085.3–2007, respectively. This suggests that the addition of BaCO3 can achieve harmless of manganese sulfate residue. Finally, the reconstructed residue is used to prepare the unfired brick with wave-absorbing. The obtained results show that the compressive strength of the brick is 17.00 MPa, meeting the standard of MU15. Additionally, the minimum reflection loss value of the brick is −10.51 dB, showing that the material has promising ability in absorbing wave.