The dissolving processes with HCl and HNO3were compared experimentally. The proportion of
dissolved CeO2with HCl was less than 25% accompanied with large consumption in raw materials and
serious pollution by Cl2, unsuitable for production. On the other hand, the proportion of CeO2dissolved
withHNO3was over 90% in the following reaction conditions: temperature 35 to 50℃, concentration of
HNO3: 7.0 to 8.5 mol/L,VH2O2:VHNO3=0.125, dissolving time: 60 min. The resolved nano-powders
were homogeneous and theirgrain sizeswere in the range of 30 to 40 nm. HNO3dissolving process saves raw
materials and there is no pollution, showing industrialized production.