Magnesium-containing Materials Research Articles

Formation and aggregation behavior of inclusions in Ni-based alloys with different Mg contents

Large non-metallic inclusions affect the mechanical properties and service life of nickel-based superalloys. This study investigates the effects of magnesium elements on non-metallic inclusions in K4169 nickel-based superalloys, exploring the formation mechanisms and aggregation relationships of the inclusions. Four gradients of the magnesium content were used to simulate the erosion of MgO refractories on inclusions in the vacuum induction melting of nickel-based superalloys. The observed inclusions mainly comprised MgO, TiN, MgAl2O4, and MgAl2O4–TiN composites. To study the formation mechanism of inclusions in Ni-based alloys with different Mg contents, the predominance diagram of Mg–Al–Ti–O inclusions in nickel-based superalloy systems was calculated using Factsage thermodynamics software and classical thermodynamics separately. The aggregation behavior of MgAl2O4 and MgO inclusions on the surface of molten nickel-based superalloys was observed in situ under a high-temperature confocal laser scan microscope. The capillary force acting on inclusions in nickel-based superalloys was calculated using the Kralchevsky–Paunov model (K–P model), the calculation was verified with experimental results, and the influencing factors were analyzed. The capillary force acting on inclusions on the surface of molten nickel-based superalloys weakened in the order of MgAl2O4 > MgO > Al2O3, which is the opposite of the order for the force acting on inclusions in molten steel. Minimizing the magnesium content in the alloy is crucial to preventing the formation of large inclusions in nickel-based superalloys, and the use of magnesium-containing materials in the smelting process should thus be avoided.

Analysis of the use of magnesium-containing additives in the charge of iron flux in order to reduce CO2 emissions

The growing requirements for the quality of finished steel products oblige to obtain steel with a low content of harmful impurities, especially sulfur. The main charge for steel production in the conditions of JSC EVRAZ NTMK is vanadium iron, the external desulfurization of which leads to large losses of valuable vanadium. Therefore, the smelting of iron with a low sulfur content is an urgent task. The main way to reduce sulfur in iron is to increase the basicity of the slag (B2), but MgO is the best desulfurizer. The paper evaluates the effectiveness of the use of various magnesium-containing materials in the conditions of the blast-furnace stage of JSC EVRAZ NTMK, taking into account CO2 emissions. The possibility of replacing limestone in the iron flux charge with dolomite, as well as with steel converter slag, is considered. Both materials will increase the proportion of MgO in blast-furnace slag, however, the use of dolomite is accompanied by a two-fold increase in CO2 emissions compared to limestone. Converter steel slag (CSS) does not contain carbonates, thus eliminating the formation of CO2 during the limestone decomposition. An additional advantage of CSS is its high content of valuable vanadium and manganese. The effect of an increase in MgO in slag on its melting point is considered. It has been established that an increase in the proportion of MgO to 14% will not cause difficulties in the processing of blast-furnace smelting products and will reduce the sulfur content in iron and the formation of titanium carbides and carbonitrides.

Intensification of the wastewater treatment process using magnesium-containing materials

An analysis was made of the use of magnesium-containing materials of natural and technogenic origin in complex systems for the purification of wastewater from mining enterprises from heavy metals. The transfer mechanisms of dissolved heavy metals into the precipitate and onto the surface of the sorbent have been theoretically studied. Magnesium-containing minerals in water partially undergo hydration, forming an association of complex molecules. The main purification mechanism is the formation of sparingly soluble metal hydroxides. The mechanisms of adsorption, co-precipitation, co-crystallization of impurities with products of hydration and hydrolysis of magnesium-containing minerals also work. Exploratory studies of the intensification of the wastewater treatment process using magnesium-containing materials have been carried out, which have shown that the residual concentration of almost all metals, with the exception of nickel and chromium, when using brucite at the same pH level is lower. The highest water purification efficiency is observed for zinc and lead ions. The addition of dolomite to brucite in an amount of less than 10% makes it possible to reduce the residual concentration of cadmium in water at 20-60 minutes of contact and other equal experimental conditions.

Development of Magnesian Cement Producing Technology on the Ural Region Raw Materials Basis

This article considers an effective way of processing natural and technogenic magnesium-containing materials, which will release magnesium oxide and magnesium sulphate for the production of magnesian cement. Using this method, pure magnesium oxide, magnesium sulphate and magnesium sulfate have been obtained, the study considers the properties of magnesian cement with differeng magnesium oxide production conditions.
 Keywords: non-conventional magnesium containing raw materials, technogenic materials, magnesian cement, hydrochemical processing, ammonium hydrosulfate

Phosphorus recovery from pig farm biogas slurry by the catalytic ozonation process with MgO as the catalyst and magnesium source

In China, most large-scale pig farms use a large-volume cover lagoon digester to treat swine wastewater and recover energy, but the effluent biogas slurry is dark in color, contains refractory organic matter, high NH3–N, and low BOD5/COD (B/C), and exhibits poor biodegradability, and it is difficult for the effluent from the wastewater treatment system to reach the standard discharge requirements. Therefore, it is necessary to study the pretreatment of biogas slurry. The purpose of this study is to use ozone to pretreat the biogas slurry, increase the ozone oxidation efficiency by adding magnesium-containing materials, simultaneously recover phosphorus (struvite) as a magnesium source, and improve the wastewater B/C. In this study, a laboratory ozone generator and ozone reactor combination device were used. The experiment investigated the effects of the magnesium material type, catalyst dosage, ozone dosage and pH on catalytic ozonation and phosphorus recovery efficiency. The results show that MgO is superior to MgCO3, dolomite and MgCl2 as a catalyst. With the addition 1.5 g/L MgO and an ozone dosage of 0.58 g/L, the COD, UV254 and chroma removal rates of biogas slurry reached 55.43%, 70.22% and 88.87%, respectively. At pH 10, the phosphorus recovery rate reached 98.47%. The SEM-EDX and XRD analyses of the phosphorus recovery product revealed that the product contained a certain amount of MAP in addition to MgO. A 3D-EEM analysis of water quality before and after ozonation of biogas slurry showed that humic acids were significantly reduced after ozonation. The GC-MS results showed that catalytic ozonation can effectively degrade refractory organic pollutants, and the biogas slurry B/C increased after pretreatment, which improved biodegradability. After ozonation pretreatment of biogas slurry, the water quality of effluent treated by a sequencing batch reactor (SBR) reached the standard discharge requirements. Using ozone to pretreat pig farm biogas slurry and adding MgO as a catalyst can not only improve ozone oxidation efficiency but also achieve phosphorus recovery. The results provide an innovative technology for the pretreatment of biogas slurry in pig farms.

Study of blast furnace heat filterability through coke filling

Increase of gas permeability of burden materials column lower part is one of the way of blast furnace heat intensification. Filterability of intermediate slag through coke filling determines the gas permeability of the lower zone and the blast furnace heat running. To study the filterability a methodology was elaborated and implemented, which enabled to estimate reliably the iron ore raw materials behavior in the blast furnace at high temperatures. By laboratory studies influence on the filterability of BF slag melt was determined, when MgO, MnO and CaO adding to the burden, depending on the oxides mineralogical composition. The positive influence of magnesium oxide on the slag filterability has an extreme character, at that the sinter basicity has a considerable influence. The mineral form of magnesium-containing additives introduced into the burden substantially influenced the filterability on heat products in blast furnace. Replace ofsiderite and dolomite by other magnesium-containing materials facilitates to improving of slag filterability through coke filling. Additional input of manganese in the form of manganese limestone or manganese-containing ferritic-calcium flux is an effective mean to improve filterability of sinter smelting products through coke filling. Transfer to hot metal smelting from fluxed pellets and sinter will facilitate heat products filterabilityincrease thanks to close physical andchemical properties of BF burden components in respect of smelting and slag filtering through coke filling.

ChemInform Abstract: A Review of Mineral Carbonation Technologies to Sequester CO2

AbstractReview: 230 refs.

Electrical Characterization of Mullite Bodies Containing Al-Rich Anodizing Sludge

Al-rich sludge produced from industrial anodising and surface treatment processes had been tested in the fabrication of mullite-based materials, by using unidirectional dry pressing as shaping technique. Mixture with common natural silica and magnesium-containing materials, like ball clay, kaolin and diatomite were prepared in order to achieve interesting final fired refractory and/or electrical insulating materials. Microstructural changes upon sintering and crystalline phase evolution are detailed and their relationship with the electrical behaviour is also studied, by the use of impedance spectroscopy. Finally, different models were used to fit the experimental electrical resistivity values and to estimate the percolation limit of the bi-phase material.

Electrical characterisation of cordierite bodies containing Al-rich anodising sludge

Al-rich sludge produced from industrial anodising and surface treatment processes had been tested in the fabrication of cordierite-based materials, by using unidirectional dry pressing and extrusion as shaping techniques. Mixtures with commercial sand and magnesium-containing materials, like ball clay, and talc were prepared in order to achieve interesting final refractory and/or electrical insulating compositions. Microstructural changes upon sintering and crystalline phase evolution are detailed and their relationship with the electrical behaviour is now studied, by the use of impedance spectroscopy.

Synthesis of cordierite from low-temperature masses based on magnesium-containing materials

Synthesis of cordierite from low-temperature masses based on magnesium-containing materials