کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
675552 887721 2007 9 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Reduction kinetics of mechanically activated hematite concentrate with hydrogen gas using nonisothermal methods
موضوعات مرتبط
مهندسی و علوم پایه مهندسی شیمی جریان سیال و فرایندهای انتقال
پیش نمایش صفحه اول مقاله
Reduction kinetics of mechanically activated hematite concentrate with hydrogen gas using nonisothermal methods
چکیده انگلیسی

The reduction kinetics of both non-activated and mechanically activated hematite concentrate in a vibratory mill for different grinding periods have been studied using themogravimetry (TG). Changes in the structure of hematite were studied using X-ray diffraction analysis. The isoconversional method of Kissinger–Akahira–Sunose (KAS) was used to determine the activation energy of the different reactions. The Vyazovkin model-free kinetic method was also used for prediction of kinetic behavior of the samples for a given temperature.Fe2O3 was found to reduce to Fe in a two-step via Fe3O4. Intensive grinding resulted in improved resolution of overlapping reduction events. It was also established that the mechanical activation had a positive effect on the first step of reduction. With increasing the grinding time, the activation energy at lower extent of conversion (α ≤ 0.11) decreased from 166 to 106 kJ mol−1 range in the initial sample to about 102–70 kJ mol−1 in the sample ground for 9 h. The complexity of the reduction of hematite to magnetite and magnetite to iron was illustrated by the dependence of E on the extent of conversion, α(0.02 ≤ α ≤ 0.95). The values of E decreased sharply with α for 0.02 ≤ α ≤ 0.11 range in the initial sample and mechanically activated samples, followed by a slight decrease in the values of E during further reduction by α ≤ 0.85 in the ground samples up to 3 h. A slight increasing dependence of E on α for mechanically activated sample within 9 h in the second step of reduction was observed due to the finely agglomerated particles during intensive milling and subsequently the formation of a dense layer during the reduction processes. In addition, the dependence of ln Aα on α was detected and it was found that the ln Aα shows the same dependence on α as the apparent activation energies.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Thermochimica Acta - Volume 454, Issue 2, 15 March 2007, Pages 69–77
نویسندگان
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