Treatment of acid mine drainage using calcined magnesite: Comparison of the effectiveness of sonication and flocculation of reaction mixtures

This study compares the effectiveness of sonication and flocculation in treating acid mine drainage (AMD) using calcined magnesite. Techniques such as X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), X-ray fluorescence (XRF), and Scanning Electron Microscopy (SEM) were used to characterize the calcined magnesite and residues. Sonication and flocculation parameters, including calcination temperature, contact time, and dosage, were evaluated in batch mode. Saturation indices of metal oxides were determined using PHREEQC geochemical modeling. The temperature of 800 °C was found to be optimal for calcining magnesite, based on MgO content (85.67%). This was also confirmed by XRD, which showed the formation of periclase, magnesium oxide mineral phase, on calcined magnesite. Sonication increased the pH from 2.25 to 10.1 within the first minutes of contact, whereas the maximum pH at the same time during flocculation was 9.2. This indicated that sonication performed better than flocculation. The product water was suitable for irrigation purposes. Sludge characterization revealed that sonication promoted more extensive mineral precipitation than flocculation. Geochemical modeling indicated that Al- and Fe-hydroxyoxides and hydroxysulphates were likely to precipitate, and that a greater diversity of minerals would form with sonication. Based on these results, sonication performs better than flocculation, and further studies are recommended to explore the potential to recover valuable minerals from AMD using sonication and calcined magnesite.