A Review on the Kinetics of Iron Ore Reduction by Hydrogen

A clean energy revolution is occurring across the world. As iron and steelmaking have a tremendous impact on the amount of CO2 emissions, there is an increasing attraction towards improving the green footprint of iron and steel production. Among reducing agents, hydrogen has shown a great potential to be replaced with fossil fuels and to decarbonize the steelmaking processes. Although hydrogen is in great supply on earth, extracting pure H2 from its compound is costly. Therefore, it is crucial to calculate the partial pressure of H2 with the aid of reduction reaction kinetics to limit the costs. This review summarizes the studies of critical parameters to determine the kinetics of reduction. The variables considered were temperature, iron ore type (magnetite, hematite, goethite), H2/CO ratio, porosity, flow rate, the concentration of diluent (He, Ar, N2), gas utility, annealing before reduction, and pressure. In fact, increasing temperature, H2/CO ratio, hydrogen flow rate and hematite percentage in feed leads to a higher reduction rate. In addition, the controlling kinetics models and the impact of the mentioned parameters on them investigated and compared, concluding chemical reaction at the interfaces and diffusion of hydrogen through the iron oxide particle are the most common kinetics controlling models.

Comparative studies on the adsorption of various radioactive nuclides from waste aqueous solutions on graphene oxide, inorganic and organic ion exchangers

Adsorption of the radionuclides 141Ce, 140La, 140Ba, 137+134Cs, 131I, 125Sb, 103Ru, 95Nb and 95Zr are studied on graphene oxide from waste aqueous solution samples and their adsorption behaviors are compared to that on the inorganic ion exchanger Ceric tungstate as well as on the strong acidic cation exchanger Dowex-50X8 H+ form, the chelating resin Chelex-100 Na+ form and the strong basic anion exchanger AG-1X8 Cl− form. The waste samples are dilute aqueous solutions resulting from previous work. These solutions contained neither oxidizing nor reducing agents, consequently, it is expected that these radionuclides are existing in their most stable oxidation states, i.e. Ce(III), La(III), Ba(II), Cs(I), Ru(III) & (IV), Sb(III) & (V), Nb(V) and Zr(IV). The adsorption is studied under static conditions for all these radioactive nuclides in the presence of each other. Gamma radiometric analysis is carried out for these radionuclides. Effect of some factors on the adsorption is studied such as pH, graphene oxide particle sizes, contact time, temperature and other parameters. Complete removal of some radionuclides is achieved from these waste solutions by adsorption on graphene oxide. Some separation alternatives for some of these radionuclides are also achieved.

Phonon Scattering and Suppression of Bipolar Effect in MgO/VO2 Nanoparticle Dispersed p-Type Bi0.5Sb1.5Te3 Composites

Bismuth-Telluride-based compounds are unique materials for thermoelectric cooling applications. Because Bi2Te3 is a narrow gap semiconductor, the bipolar diffusion effect is a critical issue to enhance thermoelectric performance. Here, we report the significant reduction of thermal conductivity by decreasing lattice and bipolar thermal conductivity in extrinsic phase mixing of MgO and VO2 nanoparticles in Bi0.5Sb1.5Te3 (BST) bulk matrix. When we separate the thermal conductivity by electronic κel, lattice κlat, and bipolar κbi thermal conductivities, all the contributions in thermal conductivities are decreased with increasing the concentration of oxide particle distribution, indicating the effective phonon scattering with an asymmetric scattering of carriers. The reduction of thermal conductivity affects the improvement of the ZT values. Even though significant carrier filtering effect is not observed in the oxide bulk composites due to micro-meter size agglomeration of particles, the interface between oxide and bulk matrix scatters carriers giving rise to the increase of the Seebeck coefficient and electrical resistivity. Therefore, we suggest the extrinsic phase mixing of nanoparticles decreases lattice and bipolar thermal conductivity, resulting in the enhancement of thermoelectric performance over a wide temperature range.

The Formation of Mn-Ce Oxide Catalysts for CO Oxidation by Oxalate Route: The Role of Manganese Content

The Mn-Ce oxide catalysts active in the oxidation of CO were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), transition electron microscopy (TEM), energy dispersive X-Ray (EDX), and a differential dissolution technique. The Mn-Ce catalysts were prepared by thermal decomposition of oxalates by varying the Mn:Ce ratio. The nanocrystalline oxides with a fluorite structure and particle sizes of 4–6 nm were formed. The introduction of manganese led to a reduction of the oxide particle size, a decrease in the surface area, and the formation of a MnyCe1−yO2−δ solid solution. An increase in the manganese content resulted in the formation of manganese oxides such as Mn2O3, Mn3O4, and Mn5O8. The catalytic activity as a function of the manganese content had a volcano-like shape. The best catalytic performance was exhibited by the catalyst containing ca. 50 at.% Mn due to the high specific surface area, the formation of the solid solution, and the maximum content of the solid solution.

Physiological performance, bromatological quality, and productivity of sweet potato using calcium oxide particle film

The objective of this work was to evaluate the effect of the application of calcium oxide (CaO) particle film on the physiological performance, bromatological quality, and productivity of sweet potato (Ipomoea batatas). The experimental design was randomized complete blocks with three treatments (5, 10, and 15% CaO particle film concentrations) and a control (water), with three replicates, applied 30 days after planting. The following parameters were evaluated: physiological, including net photosynthetic rate and Falker chlorophyll index (FCI); bromatological, i.e., crude protein, neutral detergent fiber (NDF), acid detergent fiber (ADF), total digestible nutrients (TDN), dry matter digestibility (DMD), and total carbohydrates; and productivity. The use of the 10 and 15% CaO particle film increased sweet potato photosynthesis, FCI, crude protein content, and tuber and aerial part productivity. At those concentrations, the lowest NDF and ADF contents and the highest TDN and DMD contents were also observed. The use of the CaO particle film at the concentration of 10 and 15% improves the physiological, productivity, and bromatological parameters of the sweet potato crop.