Activation Energy Of Reduction Reaction Research Articles

Effects of CaF2 on the direct reduction of beach titanomagnetite at different temperatures

AbstractEffects of CaF2 on the mineralogical composition and microstructure of reduction products at different temperatures during direct reduction of beach titanomagnetite is investigated. In the absence of CaF2, armalcolite and a large number of small‐size metallic iron particles in reduction products at different temperatures prevented the separation of Ti and Fe. The metallization rate of reduction products was only 90.32 wt% at 1350°C. CaF2 reduced the activation energy of reduction reaction and promoted the reduction of armalcolite, further achieving the separation of Ti and Fe on the mineral phase. When 5 wt% CaF2 was added at 1250°C, the metallization rate of reduction products could reach 90.88%. The effect of CaF2 on the metallization rate was better than that of increasing temperature by 100°C. Besides, CaF2 also reduced the melting point and viscosity of the roasting system, and significantly promoted the aggregation and growth of metallic iron particles, thus optimizing the conditions for the separation and enrichment of Ti and Fe, respectively. Adding 10 wt% CaF2 promoted the growth of MgTi2O5 into a mineral with regular boundary, which created conditions for the recovery of titanium resources. By comparison, the promotion effect of CaF2 on the increasing the metallization rate of reduction products, aggregation and growth of metallic iron particles was obviously better than that of increasing the reduction temperature without CaF2. Therefore, CaF2 could also significantly reduce the energy consumption on the basis of promoting the separation of Ti and Fe.

Experimental study on the high performance of Zr doped LaCoO3 for solar thermochemical CO production

Solar thermochemical CO production via CO2 splitting is an effective route to achieve carbon cycle and reduce carbon emissions. One of the most important issues for thermochemical fuel production technology is to find a material with high oxygen release capacity and fuel production as well as excellent thermal stability. Due to the excellent oxygen releasing capacity and limited fuel production and durability of LaCoO3, the feasibility of elemental doping for enhancing the redox capacity were studied in detail. Novel and high efficient redox materials, Zr doped LaCoO3 perovskites obtained were firstly used for solar thermochemical CO production. Zr doping is beneficial to improve CO yield and thermochemical redox stability. LaCo0.7Zr0.3O3, an optimum in doping for CO production, produced an average of 1066.6 μmol/g CO, which was an inspiring performance in the current perovskite based thermochemical field. The degree of reduction of LaCo0.7Zr0.3O3 was positively correlated with temperature and heating rate. Kinetics study shows that the activation energy of reduction reaction is 107.1 kJ/mol, which is much lower than that of CeO2, and the reduction process is a first order reaction. This material has better performances by comparison with CeO2 and other similar materials reported in literatures. The excellent CO production performance, pretty redox stability and kinetics manifested by LaCo0.7Zr0.3O3 provided a new approach for exploiting higher performing materials for solar thermochemical CO2 splitting.

Spectroscopic study of microstructure-reducibility relation of CexZr1−xO2 solid solutions

We have successfully elucidated the microstructures of CexZr1−xO2 solid solutions prepared by co-precipitation and their relation with the reduction behaviors. X-ray absorption spectroscopy and X-ray photoelectron spectroscopy results demonstrate that Zr(IV) occupies initially substituting site and then interstitial site in cubic CeO2. The accumulation of Zr(IV) in interstitial site induces the gradual phase transition from cubic phase to tetragonal phase. The results of selective chemisorption of methyl orange demonstrate that the substituting-site doping of Zr(IV) preferentially occurs in the bulk and then extends to the outmost surface. H2 temperature-programmed reduction results indicate that the substituting-site doping of Zr(IV) mainly enhances the reducibility of Ce(IV) whereas the interstitial-site doping of Zr(IV) not only enhances the reducibility of Ce(IV) but also lowers the activation energy of reduction reaction. These results provide novel insights into the microstructure-reducibility relation of CexZr1−xO2 solid solutions.

Mechanism of Low-Temperature Reduction Degradation of Alumina-Containing Hematite Solid Solution Below 550 °C

Low-temperature reduction degradation (LTRD) of sinter has an adverse effect on blast furnace permeability, and it is mainly caused by the stress produced in the reduction process of hematite. This stress is strongly influenced by alumina dissolved in hematite crystal lattice. In this work, the experiments were conducted to investigate the effect of alumina dissolved in hematite solid solution (Hss) on LTRD by reducing Hss below 550 °C. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), and optical microscope have been used to characterize the mass change and mineral change of samples, respectively. Jade software has been used to calculate the micro strain in magnetite for quantitatively studying the change of strain in reducing process. The results show that alumina was unfavorable to the reduction of Hss on thermodynamics, and the starting reduction temperature of Hss containing 6.0 mol pct alumina was 28 °C higher than that of pure hematite. According to the calculation on kinetics, the generation rate of stress was accelerated by dissolving alumina into hematite crystal lattice. The apparent activation energy of reduction reaction lowered from 47.89 to 28.07 kJ/mol with the increase of alumina content from 0.0 to 6.0 mol pct. The addition of alumina also increased the stress in the reduction products, and this stress was released in the form of LTRD.

Thermogravimetric study of the reduction of copper slag by biomass

The utilization of copper slag is an attractive option of iron resource. However, extra energy consumption is required and contributes to greenhouse gases. In this paper, biomass was introduced as a new kind of reductant for the reduction of copper slag to decrease the energy consumption. The reduction kinetics and reduction characteristics of three kinds of biomasses were studied by thermogravimetric analyzer (TG). The TG curves showed the reduction reaction of copper slag and biomass could be divided into three stages during heating process: drying and pyrolysis of biomass process ( 1100 K). Pine sawdust showed the best reducing property and the reduction ratios of pine sawdust, corncob and straw reached to 80.6, 76.1, and 60.0 %, respectively, when the mass ratio of biomass/slag was 2:1. As the additive, CaO had promotion effects on the reduction reaction. With the increase in CaO addition, the reduction ratio of copper slag increased firstly and reached a peak at CaO/slag was 0.3:1 and then it declined due to the changes of slag viscosity. By kinetics analysis, the reduction reaction confirmed well with shrinking core model (R1). The activation energy of reactions was affected by the addition of biomass and heating rate in experiments. With the increase in the addition of biomass, the activation energy of reduction reaction increased gradually; with the increase in heating rate, the activation energy of reduction reaction decreased.