A Novel Method of Using Iron Nanoparticles from Coal Fly Ash or Ferric Chloride for Acid Mine Drainage Remediation

Iron nanoparticles (nano Fe) were extracted from coal fly ash (CFA) or ferric chloride (FeCl3) and used for acid mine drainage (AMD) remediation. Characterisation was achieved by X-ray diffraction (XRD), X-ray fluorescence, scanning electron microscopy-energy dispersive spectroscopy (SEM–EDX), high resolution transmission electron microscopy (HRTEM), and the Braunaer–Emmet–Teller (BET) surface area determination. The HRTEM indicated good dispersion of the characteristic bead-like structure of nano Fe. It was also observed that the nano Fe were mainly in the zero-valent oxidation state, as denoted by the characteristic peak at ≈ 44.7° in the XRD analysis; it was accompanied by the generally accepted oxide layer around the particles, which was confirmed by the appearance of a core–shell structure in the HRTEM micrographs. The BET surface areas of the nano Fe extracted from the CFA or FeCl3 were recorded to be 34.7 or 88.8 m2/g, respectively. The nano Fe lowered the concentration of most of the monitored contaminants, with the percentage removal ranging from 17 to 99%. The pH of the AMD after treatment with nano Fe obtained from CFA or FeCl3 increased to 5.74 or 6.01, respectively, from 3.49, the electrical conductivity decreased to 0.18 or 0.13 Ω/m, respectively from 0.57 Ω/m, while the total dissolved solids was decreased to 447 or 384 mg/L, respectively, from 1683 mg/L. The water quality of the treated AMD is suitable for Category 4 industrial use, per the Dept. of Water Affairs and Forestry’s limits.