Under specific controlled conditions, the addition of SO2 to oxygen or atr produces the peroxy-monosulphate free radical in solution, which is a stronger oxidant than oxygen alone.The sparging of SO2/O2 or SO2/air readily oxidises Fe(Ⅱ), Mn(Ⅱ) or As(Ⅲ) in solution.In this study, the oxidation of Fe(Ⅱ) with SO2/air was investigated at 75℃ for the subsequent precipitation of Fe(Ⅲ) oxides from a synthetic nickel laterite high pressure acid leach solution containing 5 g/L Fe(Ⅱ), 1 g/L Fe(Ⅲ), 8 g/L Ni, 30 g/L Mg in sea water (~15 g/L NaCl) at pH about 2.The rate of Fe(Ⅱ) oxidation was optimised in the pH range of 1.2-2.0 with respect to SO2/air ratio and gas flow rates for minimum production of H2SO4 and maximum utilisation of SO2.The maximum rate of SO2 addition that could be employed with air whilst maintaining oxidising conditions was established to minimise the air flow rates into the reactor vessel.The results revealed strategies for commercial applications of the SO2/air oxidising system.Important factors for reactor design are suggested and the challenges in commercial scale-up for using the SO2/air system are discussed.