Modeling assessment of recovering iron from red mud by direct reduction： magnetic separation based on response surface methodology

Red mud, the waste generated during alumina production, contains iron and other valuable metals. To recover the iron efficiently from red mud, a three-factor five-level central composite design in response surface methodology was used to study the effects of process parameters, such as FC/O （the molar ratio of fixed carbon in coal to reducible oxygen of iron oxide in red mud）, reduction temperature, reduction time, and their interaction on the iron recovery rate and total iron content in magnetic product obtained from the process of direct reduction-magnetic separation. The relevant assessment model was established. The model could predict the changing rules of iron recovery rate and total iron content in the magnetic product affected by the process parameters. The results show that the iron recovery rate is significantly influenced by three factors and reduction temperature plays the most important role. The iron recovery rate and total iron content in magnetic product could be up to 98.37 and 82.52%, respectively, under the numerically optimal process parameters condition of reduction temperature of 1400 ℃, FC/O of 0.80 and reduction time of 100 min obtained by the assessment model. The predicted values are in good agreement with the experimental values.

Evolution of deformation twins with strain rate in a mediummanganese wear-resistant steel Fe-8Mn-1C-1.2Cr-0.2V

Microstructure evolutions of the medium-manganese wear-resistant steel Fe-8Mn-1C-1.2Cr-0.2V (in wt.%) with stacking-fault energy of 22 mJ m-2 during deformation at strain rate ranging of 10^-2-1 s^-1 were analyzed by means of X-ray diffraction, field emission scanning electron microscopy and high-resolution transmission electron microscopy. The results indicate that the twinning-induced plasticity effect is the main strengthening mechanism of the studied steel, whilst the transformation-induced plasticity effect only occurs at high strain rate. With an increase in strain rate, volume fraction of the deformation twins, in particular that of the secondary twins, increases significantly along with decreasing average size. When applied strain rate is higher than 10^-1 s^-1, the parallel deformation twins are turned into a crossing morphology, and the original straight twin boundaries exhibit a ladder feature, which is attributed to the interactions between regular dislocations and twin dislocations at the twin boundary. The critical strain, a key indicator of the initiation of deformation twin, decreases with increasing strain rate. In addition, the ductility and strength of medium-manganese wear-resistant steel Fe-8Mn-1C-1.2Cr-0.2V are mainly determined by the shape and volume fraction of deformation twins.

Effect of heat input on austenite microstructural evolution of simulated heat affected zone in 2205 duplex stainless steel

The effect of simulated welding thermal cycle on the microstructure and impact toughness of heat affected zone (HAZ) in 2205 duplex stainless steel was investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and room temperature impact test. The results show that the morphology and volume fraction of austenite change greatly with heat input. The amount of residual austenite and grain boundary austenite (GBA) decreases while Widmanstatten austenite (WA) laths and intergranular austenite increase with the increase in heat input. Only the fine equiaxed austenite exists in the HAZ when the heat input is increased up to 61.8 kJ/cm. WA laths nucleate initially either at the ferrite and GBA phase boundaries or directly in ferrite grains and begin to decompose into diamond-shaped austenite with the heat input larger than 25.2 kJ/cm. The impact toughness shows a non-monotonic variation, which is related to the increase in austenite fraction and the formation and the decomposition of WA laths.

Model for RuhrstahI-Heraeus （RH） decarburization process

A mathematical model was established to predict the carbon content of ultralow carbon steel in the Ruhrstahl-Heraeus （RH） process. The model was solved using the fourth-order Runge-Kutta method and assumed that the volume of steel partaking in the reaction depends on the decarburization mechanism. After analyzing the decarburization process using the proposed model, the following conclusions were drawn. First, the initial carbon and oxygen contents in the RH degasser should be stabilized in the range of （200-350） × 10^-6 and （500-700） × 10^-6, respectively. Second, in the initial stage, the pressure should be reduced as quickly as possible. Third, oxygen blowing should begin as early as possible when the forced decarburization is needed and the minimum oxygen flow rate should be 0.1923 m3/（t rain）. Finally, expanding the diameter of the snorkel tube from 480 to 600 mm clearly enhances the decarburization rate.

Wüstite-type Fe0.78Mn0.22O nanocubes:A new class for high-sensitive T2-weighted magnetic resonance imaging agent

Wüstite-type Fe(0.78)Mn(0.22)O nanocubes,with a uniform size of^10 nm in edge length,have been synthesized by thermal-decomposition approach.The nanocubes exhibited superparamagnetic properties at room temperature,associated with a magnetization of 12.6 emu/g.These Fe(0.78)Mn(0.22)O nanocubes present transversal(r2)and longitudinal(r1)relaxivities of 325.9 and 0.518 mM^-1 s^-1 at 7 T for water protons.The ratio of the r2/r1(629.2)ranks them being the highest sensitivity(r2/r1)comparable to currently reported T2-weighted magnetic resonance imaging(MRI)agents.Meanwhile,the Fe(0.78)Mn(0.22)O nanocubes were functionalized and demonstrated to be biocompatible when attached to the surface of mesenchymal stem cells,therefore showing the promise as a new class of MRI agents in clinic applications.