Influence of a Prior Oxidation on the Reduction Behavior of Magnetite Iron Ore Ultra-Fines Using Hydrogen

The reduction behavior of raw and prior-oxidized magnetite iron ore ultra-fines with hydrogen was investigated. Reduction tests were conducted with a thermogravimetric analyzer in a temperature range from 873 K to 1098 K at 1.1 bar absolute, using hydrogen as reducing gas. The experimental results show that a prior oxidation of the magnetite has a positive effect on the reduction behavior because of changing morphology. The apparent activation energies show a turnaround to negative values, depending on the prior oxidation and degree of reduction. A multi-step kinetic analysis based on the model developed by Johnson–Mehl–Avrami was used to reveal the limiting mechanism during reduction. At 873 K and 948 K, the reduction at the initial stage is controlled by nucleation and chemical reaction and in the final stage by nucleation only, for both raw and pre-oxidized magnetites. At higher temperatures, 1023 K and 1098 K, the reduction of raw magnetite is mainly controlled by diffusion. This changes for pre-oxidized magnetite to a mixed controlled mechanism at the initial stage. Processing magnetite iron ore ultra-fines with a hydrogen-based direct reduction technology, lower reduction temperatures and a prior oxidation are recommended, whereby a high degree of oxidation is not necessary.

A novel method for approximating local changes in the surface absorption for laser marking using 3D laser scanning

Laser marking is a non-contact technique, which achieves colouring by using a laser beam to increase surface oxidation. Controlling the amount of heat induced into the part is essential in ensuring the desired degree of oxidisation. However, the induced heat is not only dependent on the process parameters, but also on the surface absorption, which in turn is dependent on the material, laser wavelength, and surface quality, i.e., current degree of oxidation and contaminants as well as surface roughness. This paper proposes a method for correlating backscatter from a 3D laser scanner with the surface absorption of sheet metal parts. The purpose is to determine local changes in the surface absorption caused by surface oxidation and contamination. The method utilises a 3D laser scanner, which projects a laser line at the surface and measures the resulting backscatter at an angle. The proposed solution applies a bi-directional reflectance model to reduce the influence of varying scanning angles. The method’s sensitivity to variations in surface treatments is investigated and validated against backscatter spectroscopy measurements. The results show that the proposed method can identify changes in the absorption. However, these were, in some cases, more than 70% higher compared to spectroscopy measurements.

Numerical simulation and experimental study on hematite production by oxidation of mill scale

Mill scale is a waste product from steel hot rolling processes and containing a high amount of FeO and Fe3O4. It is crucial to recycle and reuse this waste for the recovery into a metallic iron or its single oxide derivative. One of the end products of mill scale oxidation is hematite which has multitude of uses in various application. In this present study, mill scale is converted to hematite by roasting a mixture of mill scale at a specific set of conditions at 900°C for a varied time under ambient air environment by addition of pelletized limestone as a heat storage media. In this work, the Dimensionless Degree of Oxidation Prediction Model (DDOPM) has been constructed to gain hematite purity approach in the resulting powder by using Matlab. The Buckingham Pi Theorem is used to find dimensionless parameters considering the effect of different parameters including the geometric factor of tubular horizontal furnace used, characteristic of mill scale, ambient air factor, and thermal characteristics of limestone. The degree of oxidation from experimental result was obtained from XRF analysis and compared to the result of DDOPM to show the correlation between the experimental and numerical.

Polimeryzacja aniliny w środowisku stałego pola magnetycznego

Polyaniline is an example of an electronically conducting polymer. During the oxidation of the polymer, positive charges appear in its structure, which must be compensated for e.g. by the presence of anions in the polymer layer. The form of polyaniline depends on both the degree of oxidation and the degree of protonation of the polymer, i.e. the pH of the solution. Due to the ease of electrochemical preparation of polyaniline, as well as the possibility of full control of the course of the process, the influence of the constant magnetic field (s.p.m.) on the reaction of its preparation was additionally investigated. The cyclic voltammetry (CV) method was used for this purpose. Aniline polymerization processes were carried out on platinum, plate electrodes, not insulated (A) and insulated on two different sides with Teflon, with surfaces directed parallel to the line of force of the s.p.m. (To beat). Research on the electrochemical preparation of polyaniline in s.p.m. allowed to conclude that the following factors affect the magnitude of the current in the tested process: (i) the magnitude of the magnetic induction vector B, (ii) the position of the electrode plane in relation to the direction of the vector B, (iii) the type of electrode (insulated on one side or not). Impact on the impact of s.p.m. the magnetic properties (e.g. paramagnetic, diamagnetic) of the particles participating in the electrochemical reaction, as well as their charge (+/-), also had an effect on the electrochemical polymerization processes. Based on the experimental results, the mechanism of the influence of s.p.m. was proposed. on the tested electrochemical reactions. This mechanism was based, inter alia, on the formation of the magnetohydrodynamic effect (MHD), which causes a change in the speed of transport of the reacting substances to the electrode, the magnetohydrodynamic movement of the electrolyte and the change in the kinetics of electrode processes. For the tested process, changes in the rate constants of electrochemical reactions (ks) as a result of external action of s.p.m. were around 30%.

Petrological and geochemical characteristic of the rocks of the Voznesensky intrusive massif (Southern Urals): Оn the question of the composition and sources of magma producing gold and copper porphyry mineralization

Research subject. The petrological and geochemical features of the rocks of the Voznesensky intrusive massif and its dyke series were studied in order to clarify the composition, possible sources and geodynamic settings of magma generation that produced Au- and Cu-porphyry mineralization.Methods. The content of petrogenic oxides was determined by the chemical method, trace elements – by ICP-MS analysis.Results. Among the rocks of the Voznesensky massif, which have the geochemical characteristics of suprasubduction formations, varieties with calc-alkaline and adakite-like properties were established. The main phase of the massif is represented by gabbro-diorites and diorites belonging to the calc-alkaline series. Ore-bearing dykes of gabbro-diorites, diorites and granodiorites of the Au-porphyry Bolshekaransky deposit are of calc-alkaline composition, while the post-ore dykes of granodiorites and plagiogranites of this deposit exhibit adakite-like characteristics.Conclusions. The ore-bearing dyke series of the Voznesensky deposit is represented by calc-alkaline diorites and adakite-like granodiorites and plagiogranites. The metallogenic specialization of the dykes was influenced by the silicic acidity and the redox state of the ore-generating melts. Granitoids with Cu-porphyry mineralization, compared to their gold-bearing varieties, crystallized from more acidic melts with a higher degree of oxidation. It is assumed that the main mantle component of magmas for the Voznesensky rocks were relatively weakly depleted spinel peridotites of the suprasubduction lithospheric mantle. Calc-alkaline magmas were melted from a mantle substrate previously metasomatized by aqueous fluids, and magmas with adakite-like properties – metamorphosed by melts of basalts and sedimentary rocks of slab. Melting of slab rocks may have been associated with additional heating due to friction caused by changes in direction and/or velocity of oblique subduction.