Xing-le Liu

Reduction of Pyrite Cinder Pellets Mixed with Coal Powder

Direct reduction of pyrite cinder in a rotary hearth furnace (RHF) was studied under the condition of laboratory simulation. Effects of reduction temperature, reduction time, molar ratio of carbon to oxygen, and CaO addition on metallization rate as well as compressive strength of the pellets after reduction were discussed. The results showed that the metallization rate and compressive strength were 93.9% and 2160 N per pellet respectively under the conditions of the reduction temperature of 1200 °C, the reduction time of 16 min, and the molar ratio of carbon to oxygen (xc/xo) of 1.0; adding 2. 5 % CaO was beneficial to sulfur enrichment in slag phase of pellet, and metallization rate increased slightly while compressive strength decreased.

Effects of magnesium olivine on the mineral structure and compressive strength of pellets

ABSTRACT To study the effect of magnesium olivine on the compressive strength, phase composition and mineral structure of magnetite pellets, six groups of pellets were prepared by changing the content of olivine and the pellets were further subjected to the preheating and roasting processes in tube furnaces. Scanning electron microscopy-Energy dispersive spectrometer (SEM-EDS), X-Ray diffraction (XRD) and Mercury injection apparatus were used to characterise the microstructure and porosity of pellets. Results showed that four types of phases exist in pellets, which are hematite, (Mg,Fe)O–Fe2O3, silicate and incompletely mineralised magnesium olivine. With the addition of olivine, hematite phase content in pellets decreases while other phases tend a varying degree of increase. Mg in pellets mainly exists in the form of (Mg,Fe)O–Fe2O3 and small part in the phase of silicate and incompletely mineralised magnesium olivine. Compressive strength of pellets decreases with the increase in magnesium olivine content. That is mainly because of the increasing porosity and impeded recrystallisation of hematite. The existence of incompletely mineralised magnesium olivine would both increase the porosity and hinder the connect of hematite particles; thus it is not conductive to the strength of pellets.

Thermal performance and reduction kinetic analysis of cold-bonded pellets with CO and H2 mixtures

Cold-bonded pellets, to which a new type of inorganic binder was applied, were reduced by H2–CO mixtures with different H2/CO molar ratios (1:0, 5:2, 1:1, 2:5, and 0:1) under various temperatures (1023, 1123, 1223, 1323, and 1423 K) in a thermogravimetric analysis apparatus. The effects of gas composition, temperature, and binder ratio on the reduction process were studied, and the microstructure of reduced pellets was observed by scanning electron microscopy–energy-dispersive spectrometry (SEM-EDS). The SEM-EDS images show that binder particles exist in pellets in two forms, and the form that binder particles completely surround ore particles has a more significant hinder effect on the reduction. The reduction equilibrium constant, effective diffusion coefficient, and the reaction rate constant were calculated on the basis of the unreacted core model, and the promotion effect of temperature on reduction was further analyzed. The results show that no sintering phenomenon occurred at low temperatures and that the increasing reaction rate constant and high gas diffusion coefficient could maintain the promotion effect of temperature; however, when the sintering phenomenon occurs at high temperatures, gas diffusion is hindered and the promotion effect is diminished. The contribution of the overall equilibrium constant to the promotion effect depends on the gas composition.

Strengthening Reduction Process of Vanadium Titanao‐Magnetite with CaF2 Added at High Temperature

Experiments were carried out by adding CaF2 as catalyst in a Ar atmosphere to study the isothermal reduction kinetics of vanadium titano-magnetite carbon composite pellets under high temperature in the range from1473 to 1673K. By analyzing reduction mechanism, it was found that the rate controlling step was gas diffusion, and the activation energy was 178.39kJ•mol−1 without adding any catalysts. Adding CaF2 of 3% to vanadium titano-magnetite carbon composite pellets can decrease the apparent activation energy of reduction, and the decrease extent was 14.95kJ•mol−1. In addition, temperature is an important factor influencing on reaction rate.