Simultaneous thermogravimetry and differential scanning calorimetry analysis （TG-DSC） and physical phase analysis was conducted to study the characteristics of oxidizing roasting of RO phase. Solubility of the products of RO phase oxidizing roasting in acetum and the leaching effect of the inert mineral roasting material in acetum were investigated. The results show that the oxidizing roasting process can be divided in three stages： preservation of the original mineral phase， primary oxidation reaction， and secondary oxidation reaction. The primary oxidation products are type Ⅰ pleonaste， and the secondary oxidation products are type Ⅱ pleonaste and periclase. The two types of pleonaste are both insoluble in acetum. After RO phase oxidizing roasting to form pleonaste， total Fe（TFe） loss during acetum leaching can be avoided. After oxidizing roasting at medium or high temperature， the TFe mass loss rate of the inert mineral product reduced by 98.2% during acetum leaching.