To reduce the volume of precipitates generated by the neutralization of acid mine drainage (AMD) containing high concentrations of Fe and As, the formation of ferrite using the precipitates was attempted by a two-step neutralization process in which calcium carbonate (CaCO3) was used as the first neutralizer and sodium hydroxide (NaOH) as the second. Batch neutralization experiments with CaCO3 and continuous flow experiments by the two-step neutralization were conducted in the laboratory and in an AMD treatment plant. The results showed that the precipitation of Fe, Al, Si, and As was primarily determined by pH and not by the kind of neutralizer. The precipitates in the ferrite sedimentation tank were magnetized in the continuous flow experiments, although the Al and Si prevented the generation of ferrite in the AMD and the precipitates contained calcite and gypsum as impurities. The molar ratio of As to Fe in the precipitates in the CaCO3 sedimentation tank was estimated at approximately 0.01 at 2<pH<5. This suggests the coprecipitation of As and Fe. The mass balance calculation based on the results of the AMD treatment adopted here suggests that the amount of precipitates produced by ferrite formation is reduced by 15% for CaCO3 and 67% for MgO compared with a conventional treatment.