Magnetite and inorganic sludge were mainly composed of Fe2O4 and Fe2O3, respectively. Initial specific surface areas of magnetite and inorganic sludge were 130 m2/g and 31.7 m2/g. CO2 decomposition rate for inorganic sludge was increased with temperature. Maximum CO2 decomposition rates were shown 89% for magnetite at 350℃ and 84% for inorganic sludge at 500℃. Specific surface area for magnetite was not varied significantly after CO2 decomposition. However, specific surface area for inorganic sludge was greatly decreased from initial 130 m2/g to approximately 50~60 m2/g after reaction. Therefore, it was estimated that magnetite could be used for CO2decomposition for a long time and inorganic sludge should be wasted after CO2 decomposition reaction.

This research was conducted to estimate the characteristics of carbon dioxide decomposition using an inorganic sludge. The inorganic sludge was composed of high amount (66.8%) of Fe2O3. Hydrogen could be reduced with 0.247, 0.433, 0.644, and 0.749 at 350, 400, 450, and 500℃, respectively. The carbon dioxide decomposition rates at 250, 300, 350, 400, 450, and 500℃ were 32, 52, 35, 62, 75, and 84%, respectively. High temperature led to high reduction of hydrogen and better decomposition of carbon dioxide. The specific surface area of the sludge after hydrogen reduction was higher than that after carbon dioxide decomposition. The specific surface area of the sludge was more decreased with increasing of temperature.

ZnxFe3-xO4(0.00.<X<0.08) was synthesized by air oxidation method for the decomposition of carbon dioxide. We investigated the characteristics of catalyst, the form of methane by gas chromatograph after decomposition of carbon dioxide and kinetic parameter. ZnxFe3-xO4(0.00.<X<0.08) was spinel type structure. The surface areas of catalysts(ZnxFe3-xO4(0.00.<X<0.08)) were 15~27 m2/g. The shape of Zn0.003Fe2.997O4 was sphere. The optimum temperature for the decomposition of carbon dioxide into carbon was 350℃. Zn0.003Fe2.997O4 showed the 85% decomposition rate of carbon dioxide and the degree of reduction by hydrogen(δ) of Zn0.003Fe2.997O4 was 0.32. At 350℃, the reaction rate constant and activation energy of Zn0.003Fe2.997O3.68 for the decomposition of carbon dioxide into carbon were 3.10 psi1-α/min and 0.98 kcal/mole respectively. After the carbon dioxide was decomposed, the carbon which was absorbed on the catalyst surface was reacted with hydrogen and it became methane.