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

• Published in: International journal of minerals, metallurgy and materials metallurgy and materials, 2018-07, Vol.25 (7), p.752-761
• Main Authors: Wang, Rong-rong, Zhang, Jian-liang, Liu, Yi-ran, Zheng, An-yang, Liu, Zheng-jian, Liu, Xing-le, Li, Zhan-guo
• Format: Article
• Language: English
• Subjects: Binders (materials); Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Composites; Corrosion and Coatings; Diffusion coefficient; Diffusion rate; Gas composition; Gaseous diffusion; Glass; High temperature; Low temperature; Materials Science; Metallic Materials; Mixtures; Natural Materials; Pellets; Reduction; Scanning electron microscopy; Sintering; Spectrometry; Surfaces and Interfaces; Temperature; Temperature effects; Thermogravimetric analysis; Thin Films; Tribology
• ISSN: 1674-4799; 1869-103X
• DOI: 10.1007/s12613-018-1623-6

Cold-bonded pellets, to which a new type of inorganic binder was applied, were reduced by H 2 –CO mixtures with different H 2 /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.