Feasibility of using metakaolinite for the treatment of coal-mining acid mine drainage: insights into the interaction behaviour and partitioning of inorganic contaminants

In this novel study, the efficacy of metakaolinite for the treatment of acid mine drainage (AMD) was evaluated. The optimized parameters included the feedstock dosage and contact time. Experimental results were further explored using inductively coupled plasma–mass spectrometry (ICP–MS), ICP–OES (inductively coupled plasma–optical emission spectroscopy), Fourier transform infrared spectroscopy (FTIR), high-resolution–focused ion beam/scanning electron microscopy (HR–FIB/SEM), energy-dispersive x-ray spectroscopy (EDS), x-ray fluorescence (XRF) and x-ray diffraction (XRD). Optimum conditions were observed to be 45 min of mixing time, ≥10 gꞏL−1 of feedstock dosage, i.e., metakaolinite, and ambient temperature and pH. The metal content (Fe, Mn, Cr, Cu, Ni, Pb, Al, and Zn) embedded in AMD matrices were partially removed whilst the level of sulphate was significantly reduced. Chemical species removal efficacies were observed to occur in the following sequence; Cr ≥ Zn ≥ Cu ≥ Pb ≥ Mn ≥ Ni ≥ sulphate ≥ Mg ≥ Fe, with the following removal percentages: 100, 91.7, 74.6, 65, 38.8, 37.5, 32.3, 13.8, and 8.3%, respectively. Thus metakaolinite proved to be partially effective in the treatment of AMD emanating from coal-mining processes. Furthermore, to enhance the performance of this technology, a polishing technique needs to be coupled or integrated to further remove residual inorganic contaminants, as well as other forms of modification such as the addition of alkaline agents to synthesize the nanocomposite and increase its alkalinizing capabilities.