The kinetics of voluminal reduction of chromium ore fines containing coal （COFCC） by microwave heating was studied. When the molar ratio of carbon to oxygen was 0.84 and that of CaO to SiO2 was 0.39 in COFCC, the temperature rising rate of COFCC by microwave heating was 62.5 ℃/min, 68.75 ℃/min, 70. 59 ℃/min, and 72.22 ℃/min at 1 000 ℃, 1 100 ℃, 1 200 ℃, and 1 300 ℃, respectively. The results show that the voluminal re duction of COFCC by microwave heating at solid-solid phase is first order reaction, with the apparent activation energy of 51. 480 kJ/mol. The limiting step of reaction rate for the overall reaction is the mass transfer of CO in the reduced product layer between dielectric particles of chromium ore and coal.
To avoid the nonuniform phenomena of heat and mass transfer of metallurgical powdery materials caused by conventional heating method,the temperature rise characteristics of carbon-containing chromite ore fines in the microwave field were investigated using microwave heating in a microwave metallurgical furnace.The experimental results show that the carbon-containing chromite ore fines have better temperature rise characteristics in the microwave field at a frequency of 2.45 GHz.After heated in the microwave field of 10 kW,the temperature of 1 kg carbon-containing chromite ore fines rose up to 1 100 ℃ in 7 min,at a temperature rise rate of 157.1（℃·min-1·kg-1）,whereas the temperature of 1 kg carbon-containing magnetite ore fines rose only up to 1 000 ℃ in 10 min,at a temperature rise rate of 100（℃·min-1·kg-1）.With increasing carbon-fitting ratios and by adding calcic lime,their heating effects changed regularly.
LI NingCHEN JinYAN HongFENG Xiu-meiCUI Hui-junLIU Jin-ying
Chromium ore fines containing coal (COFCC) can be rapidly heated by microwave to conduct the voluminal reduction, which lays a foundation of getting sponge ferrochromium powders with a lower content of C. Under the conditions of COFCC with n(O)-n(C) (molar ratio) as 1.00-0.84 and n(SiO2)-n(CaO) as 1.00-0.39, the samples were heated by 10 kW microwave power to reach the given temperatures and held for different times respectively. The results show that the low-C-Cr ferrochromium metal phase in the reduced materials forms before the high-C-Cr ferrochromium metal phase does. With increasing temperature the C content of ferrochromium metals is in a positive correlation with the content of Cr. The C content of ferrochromium metal in reduced materials is 0-10.07% with an average value of 4.68%. With the increase of holding time the Cr content in ferrochromium metals is in a negative correlation with the content of C, while the content of Fe changes in the contrary way. In the microwave field the kinetic conditions of carburization are closely related with the temperature of microwave heating, holding time and carbon fitting ratio.
