The concentrations of metals were determined using ICP-OES (iCap 6500 Duo, Thermo Scientific, UK) before and after oxidation process to check if ferrate (VI) ions could reduce or completely remove them from synthetic AMD. The main target elements to be removed in this study were Fe, Mn and Zn. Iron was selected during AMD treatment as it is the main element causing the acidity in this type of water during its oxidation while Mn and Zn are barely removed from the water at pH less than 9.5. Before oxidation process, synthetic AMD (ca. 400 mg Fe 2+ /L) was diluted to 100 times by taking 1mL of the sample into 99 mL of deionized water and filtered at 0.22 µm. The calibration curve ranging from 0 to 7.5 mg/L for all metals was prepared using a multielement standard solution. Treated synthetic AMD was first centrifuged and the supernatant liquid was filtered using the same size of filters. All samples were run in triplicate on ICP-OES.