Solid State Reduction of Preoxidized Chromite-iron Ore Pellets by Coal

Abstract

A comparative study on coal-based solid state reduction of preoxidized chromite pellets and chromiteiron ore pellets was conducted to investigate the reduction behavior of these two types of pellets. And the enhancement mechanism of chromite reduction reactions due to the pre-oxidation process of chromite with magnetite was revealed by means of optical microscopy, SEM with EDS. The results show the presence of iron ore and pre-oxidation process both are advantageous to the reduction of chromite. Preoxidation of chromite and iron ore mixture at 1 323 K for 15 min contributes to more formation of sesquioxide solid solution (Fe, Cr, Al)2O3 than pure chromite oxidation. Massive cations exchange and diffusion occur between chromite and iron ore, which normally cause the decrease of magnesium content and aluminum content and the increase of iron content in spinel solid solution. Accordingly, the chromite reduction is enhanced with the metallization rate of chromite raised from 20.83% in prereduced chromite pellets to 47.98% in prereduced composite pellets at temperature of 1 473 K for 90 min and C/O ratio=1.06, but no further improvement is observed above 1 473 K. The mechanism study based on carbothemic reduction thermodynamics and the microstructure of prereduced pellets reveals the reduction of sesquioxide solid solution (Fe, Cr, Al)2O3 is more thermodynamically supported and the high iron, low magnesium and aluminum spinel solid solution formed in pre-oxidation process is also favorable for chromite reduction because of lower outward diffusion resistance of Fe 2+ to the interface with CO gas.

Recycling pre-oxidized chromite fines in the oxidative sintered pellet production process

“…The maghemite phase then decomposes to the more stable hematite (Fe 2 O 3 ) phase at elevated temperatures (> 600ºC) in the presence of oxygen (P O 2 = 0.2 atm.) (Tathavakar et al, 2005;Pan, Yang, and Zhu, 2015). The presence of Al 3+ cations increases the oxidative decomposition temperature as they can occupy vacancies present in the maghaemite structure (Hellwege and Hellwege, 1970).…”

Experimental Analysis of Image Dehazing Algorithms for Pelletization Process Images

“…Xin WU, 1,2) Xiaoyan LIU 1,3) * and Fei YUAN 1) 1) College of Electrical November 11, 2020) The product quality of pelletization process in steel industry is usually monitored by machine vision system. However, the image quality deteriorates significantly by haze generated during pelletization.…”

“…Pellet size distribution is an important quality control index, because it greatly affects the energy consumption and producing efficiency in the following sintering process in blast furnace. [1][2][3] In recent years, machine vision has become a popular method for online monitoring the size distribution of green…”

Preliminary reduction of chromium ore using Si sludge generated in silicon wafer manufacturing process

“…However, in the case of chromium, there is no way to distinguish precisely the chromium present as an oxide from the chromium present as a metal by chemical analysis or XRF. Therefore, similarly as the work of Kapure et al [21] and Pan et al [24], in this study the reduction of chromium is indirectly evaluated by defining the reduction ratio based on the iron content,as given below…”

“…Because of this, the reduction rate for 1388 °C was not presented in Figure13. Pan et al [24] reported that the reduction rate varies from 20.8% to 33.8% depending on the temperature in the solid phase chromium ore reduction by coal. They reported the reduction rate of 32.6% for the reduction of 90 minutes at 1300 °C, which is slightly higher than the reduction rate of this study.…”