Papers by Keyword: Hematite

Abstract: Spark Plasma Sintering (SPS), also known as pulsed electric current sintering (PECS) or field assisted sintering technology (FAST), belongs to a class of powder metallurgy methods. Investigations of the effect of thermal, electric and electromagnetic fields arising under the conditions of spark plasma sintering of ceramic materials on their final characteristics are of important fundamental scientific significance. In this regard, the work investigated the effect of the IPA temperature on the structure, composition and magnetic properties of hematite α-Fe₂O₃ of high purity 99.995%. Changes in the structure and composition of ceramic specimens under SPS conditions in the temperature range 800-1000°C are described by scanning electron microscopy and X-ray phase analysis. The magnetic properties are studied and the regularities of changes of the magnetization (M_s) and coercive force (H_c) under the influence of an external magnetic field for ceramic samples are determined depending on the temperature of the SPS. These results can be considered as initial study of the process of consolidation of materials with weak ferromagnetism under conditions of spark plasma sintering.

Abstract: Hematite is one of the most stable oxide phases and has been used as a rock-art pigment material in the prehistoric era. Hematite in the form of ochre has been widely used in rock art, burial rites, cosmetics, and decorations on pottery surfaces. Hematite has several hues, ranging from red to black. The variety of hues might arise due to the differences in physicochemical properties of hematite such as crystallinity, crystallite size, morphology, and electronic structure. The differences in physicochemical properties in hematite pigments might be originated from the differences in the pretreatment technique used before application. Herein, we have conducted a thorough study to investigate the evolution of the crystal structure of hematite under various temperatures. We aim to determine the temperature needed to change the hematite color and uncover the transformation of crystallographic properties as a function of sintering temperature. The hematite was synthesized using the precipitation method with Fe (NO₃)₃.6H₂O as a precursor and ammonia (NH₄OH) solution as a precipitating agent. The study of the hematite structural evolution was carried out by varying the sintering temperatures from 600 to 900 °C and analyzing the products after sintered using X-ray diffraction technique. The results showed that hematite hue was gradually darkened as the sintering temperature increased as a consequence of higher crystallinity and larger crystallite size of hematite crystal. This study confirms that the origin of color changes in hematite is due to the heating treatment of hematite material.

Abstract: Bioleaching solutions from uranium and arsenic solid waste served as a source of U(VI) and As (V) ions, while plant extract from green tea (Camellia sinensis) – as a reductor for nanoparticle synthesis. Uranium dioxide and As (III) nanoparticles were formed as a product of bioreduction on the hematite and schwertmannite surfaces respectively, which resulted in an increase in the negative zeta potential with an increase in pH. It suggests, that the electrical potential depends on the presence of nanoparticles. The SEM microphotographs revealed the UO₂ nanoparticles on the hematite surface.

Abstract: There are two types of iron resources such as primary iron ore and iron sand. In general, primary iron ores use as raw materials in iron and steel making and can reduce directly. In Direct reduction process, Fe₂O₃ (hematite) is converted to metallic iron by the removal of oxygen. This work presents a heat transfer rate study for direct reduction process of iron ore cylindrical briquette. An investigation has been carried out of different reduction parameter such as different sizes cylindrical geometry over temperatures ranging from 700°C to 1100°C for reaction time from 10 minutes to 1 hour. The result was indicated that the value of the heat transfer rate decreases in the core and outer parts of the cylinder briquettes.

Abstract: The mineral processing technology of Anshan-type iron ores has been developed in a rapid speed in recent years, and the combined flowsheet at the core of anionic reverse flotation has become a mainstream in the beneficiation of Anshan-type iron ores in china. With the successful application of this combined flowsheet, some obvious problems are also emerging. Such as high requirement of pulp temperature, complex reagent system, high cost of reagent consumption and so on. In view of this,we have carried out an experimental study on the separation of Anshan type iron ore by cationic reverse flotation . A new collector (named KBD) which is mixed amines have been developed . On this basis, the actual mineral separation experiment is carried out in the laboratory.With KBD as the collector,and starch and sodium hexametaphoshate as the depressant, has resulted in an iron concentrate of 68.16% and recovery rate of 89.71%. The determination of the electrokinetic potential and the infra-red spectroscopic analysis show that KBD can effectively and priorly adsorbed to the surface of quartz, and has greatly change the elecrtokinetic potential of quartz.The interaction of the depressing agent has increased the differences of the floatabilities in quartz and hermitite and changed the surface electric property so that the effective separation has been realized.

Abstract: On the basis of the experimental data, a method and mechanism for modifying magnesia binders with iron ore concentrate has been proposed. It consists in form of a material reinforced fine-crystalline structure with elongated magnesium oxychloride crystals, which improves its physical and mechanical characteristics. The components of iron ore concentrate and magnesia binder, having improved sorption properties, significantly accelerates the formation of such a structure.

Abstract: The paper presents the results of the research for the reasons of the formation of a brownish bloom on a light clinker brick during its operation. In the work course, the clinker bricks, their mineralogical composition, the nature of the secondary brick coloring and the base materials were tested during bricklaying. It was established that 2 factors caused incrustation. Firstly, the site on which the clinker brick was laid was characterized by a level of alkali soil water close to the surface, and the surface evaporation prevailed over the soil absorption in the warm period of the year. That is all soil water-dissolved salts migrated to the surface of the brick along well-permeable sand joints between the bricks. Secondly, ferrous minerals, including hematite, which was subjected to hydration with the formation of iron hydroxides, and also reacted with sulphates of groundwater with the formation of iron sulphates, were found in the foundation under the brick. This confirms the higher sulfur content in incrustation areas and the presence of a film similar to crystalline hydrates. The analysis of the research allowed us to develop the recommendations for the performance of paving various types of sites with clinker bricks, to develop measures to eliminate an existing bloom, and also to defend the “honor and dignity” of light bricks.

Abstract: The Nimba Range and its western extension are located in the Nimba region on the borders of the Republic of Guinea, Liberia and Côte d'Ivoire. It is a mountainous region made up of metavolcanic and metasedimentary rocks. Metavolcanic rocks are gneisses, granites, amphibolites and quartzites, which constitute the lower part of Archean age. The upper part consists of Proterozoic rocks of metasedimentary origin. It contains important deposits of itabirites which occupy the top of the mountains and hills of the region. The petrographic study of the banded iron formations reveals the existence of silicate banded iron formations (SIF) and oxidized banded iron formations (OIF). The results of the scanning electron microscope (SEM) and metallogenic analyzes show the presence of iron minerals (magnetites, hematites, pyrites, goethites, martites and siderites). These analyzes also reveal the presence of the metamorphic index minerals associated with the banded iron formations, hence the existence of several types of ferriferous formations (silicate (SIF) and oxidized (OIF) banded iron formations). Overall, there is an increase in the degree of regional metamorphism from east to west of the Nimba region. The geochemical analysis of the banded iron formations reveals that with the exception of Na₂O, all the major elements have a negative linear correlation although dispersed with Fe₂O₃. This correlation is explained by a decrease in quartz, garnet, micas (muscovite and biotite), amphibole, pyroxene, plagioclase, titanium and phosphorus contents. Conversely, there is an increase in iron ore content: magnetites, pyrites, hematites, goethite. But the alkali content remains constant in these banded iron formations. Then, the lower the Fe₂O₃ content, the higher the FeO content, while those of SiO₂ and Al₂O₃ are constant in all of these formations in the Nimba region except in the chlorite banded iron formation where both are anticorelated. Finally, the ratio SiO₂ / Fe₂O₃ vs MgO + CaO + MnO / Fe₂O₃ of the banded iron formations of the Nimba region compared to the same formations of the whole world allows to give them Proterozoic age. Some itabirites have high levels of magnetite, hematite, and goethite (same feature as itabirites of Lac supérieur and Pic de fon) and only chlorite itabirite has a low to medium Mg-Si-BIF content.

Abstract: This study reports on the development of an iron oxide-cellulose composite material for the controlled removal of 4-hydroxy-3-nitrobenzenearsonic acid (roxarsone), a model organoarsenical. Hematite (He) and a hematite-cellulose (HeCell) composite adsorbents were prepared and characterized by thermal gravimetric analysis (TGA), nitrogen adsorption, and various spectroscopic (IR, Raman, XRD, and TEM) methods. The uptake of roxarsone at ambient conditions of He and HeCell, and goethite-cellulose (GoCell) adsorbent were compared to study the factors that influence adsorption. The monolayer adsorption capacity (mmol/g) of each adsorbent are listed in parentheses, as follows: cellulose (0.028), goethite (0.0730), Hematite (0.155), 10 % Fe coated GoCell (0.0222) and 10% Fe coated HeCell (0.0873). The relatively large surface area of hematite nanoparticles (NPs) and good dispersion of these NPs onto the cellulose supports contribute to their effective adsorption of roxarsone.

Abstract: Temperature-programmed reduction (TPR) is a widely used method for characterization of oxide-based catalysts, sorbents, and functional materials, but its results lack quantitative assessment. Here, we present a novel approach to kinetic analysis of the TPR that can be applied to a large variety of systems involving multiple limiting stages. Implementation of cubic splines to approximate rate constant vs. conversion dependencies obtained from several TPR curves recorded at different heating rates yields in a set of kinetic parameters (activation energy and preexponential factors) for all reduction stages. Relationship between preexponential factor of the first reduction stage and the specific surface area of the sample has been shown. Reduction of hematite has been studied to prove the performance of the developed kinetic analysis technique.