Synthesis and characterization of magnetic nanoparticles and study their removal capacity of metals from acid mine drainage

• Increased temperature and pH resulted in well crystallised MNPs.
• Usage of NH4OH and NaOH limited incorporation of calcium and magnesium into ferrite.
• Higher degree of crystallinity of MNPs synthesised when NH4OH was used than NaOH.
• Treating AMD with MNPs accelerated ferrite formation and increased magnetic moment.
• Under different conditions mixtures of ferrite MNPs were produced from AMD.

In this study, the possibility of synthesising magnetic nanoparticles (MNPs) with and without heat from pure chemicals and real acid mine drainage (AMD) by co-precipitation method was explored. In addition, the influences of temperature, pH and stirring time on the crystalline size of MNPs were studied. The results revealed that possibility of synthesising Fe3O4 and CoFe2O4 from their corresponding binary salts under these conditions. Further, the method was applied on simulated and real AMD; however, formation of well crystalline MNPs at lower pH and temperature from both samples were hampered due to interfering and combined effect of the metal cations. Increasing pH and temperature increased crystalline size of synthesised MNPs as confirmed by XRD results. Similarly, these observations were further reflected by the formation of Fe3O4, γ-Fe2O3, Mn3O4, MnO2 and ZnO mixtures as major components from real AMD. Treating AMD in the presence of MNP seeds accelerated formation of ferrite and resulted in increased magnetic moment of ferrite sludge. Under all conditions, higher intensity and better resolution of XRD peaks of synthesised MNPs were obtained when NH4OH (aq.) was used for neutralization than NaOH (aq.). In general, this study demonstrates that the possibility of converting environmental pollutants into commercially valuable chemicals.