Wt Pct MgO Research Articles

Phase Equilibrium studies in the system “FeO”–SiO2–Al2O3–CaO–MgO at 1200 °C and Po2 10-8atm

Iron oxides and silica are the major components of copper smelting slag. The oxides of aluminum, calcium and magnesium are also present in the slag that is introduced through copper concentrate, flux and refractories. Liquidus temperatures of the copper smelting slags are usually controlled by Fe/SiO2. The concentrations of Al2O3, CaO and MgO, and FeO/Fe2O3 in the slag can also affect the liquidus temperatures where FeO/Fe2O3 is a function of oxygen partial pressure. High temperature equilibration under controlled oxygen partial pressure followed by quenching and electron probe microanalysis were used to determine the compositions of the liquid and solid phases at 1200 °C and Po2 10-8 atm. The experimental results are presented in the forms of pseudo-ternary sections “FeO”-CaO-SiO2 at fixed 2, 4 and 6 wt pct MgO, and 2 + 2, 4 + 4 and 6 + 6 wt pct MgO + Al2O3. Spinel and tridymite are the major primary phases in the composition range investigated. In addition, CaSiO3, pyroxene, olivine, and melilite are also present. The isotherms in the spinel and tridymite primary phase fields move towards higher SiO2 concentration directions with increasing CaO, Al2O3, and MgO concentrations. The experimentally determined results are compared with the FactSage calculations.

Phase Equilibria in the TiO2-Rich Part of the TiO2-CaO-SiO2-10 Wt Pct Al2O3-5 Wt Pct MgO System at 1773 K

The phase equilibria of the TiO2-CaO-SiO2-10 wt pct Al2O3-5 wt pct MgO system in the TiO2-rich part were investigated experimentally at 1773 K using the high-temperature equilibration–quenching method and the electron probe microanalyses. Through this study, the isothermal section of the above system was obtained containing one liquidus region and five solid–liquid coexistence regions. The primary phase region of anosovite was not only found, but it is the optimal composition region that is most beneficial to the anosovite selective crystallization and separation. The phase diagram of the TiO2-CaO-SiO2-10 wt pct Al2O3-5 wt pct MgO system in the TiO2-rich corner at 1773 K has been established. The obtained phase diagram can provide reliable reference for the slag adjusting during vanadium-titanium magnetites smelting to make sure the resulting Ti-bearing slag can be upgraded using the selective crystallization and phase separation method.

Precious Metal Distributions in Direct Nickel Matte Smelting with Low-Cu Mattes

Base metal (Cu, Fe, and Ni) and trace element (Ag, Au, Co, Pd, and Pt) distributions between low-iron nickel mattes with [Ni]:[Cu] = 4 (w/w) have been studied at 1623 K to 1723 K (1350 °C to 1450 °C). We equilibrated small slag–matte samples with CO–CO2–SO2–Ar atmospheres in pre-selected \( P_{{{\text{S}}_{2} }} \)–\( P_{{{\text{O}}_{2} }} \) points, maintaining silica saturation by fused silica crucibles. The slags studied contained about 0 to 8.5 wt pct MgO. The matte–slag distribution coefficients L m/s[Me] were obtained from assays by electron probe X-ray microanalysis for the matte and by laser ablation-ICP-mass spectrometry for the slag. The measured L m/s[Me] values were clearly dependent on iron concentration of the matte and on MgO concentration of the slag, with values on the order of 104, 105, and 104 for gold, platinum, and palladium, respectively, in the 5 wt pct iron in matte experiments. The obtained data for silver were scattered, due to volatilization, resulting in depletion of most silver and its escape from matte to gas phase during the 3-hour equilibration period. The matte-to-slag distribution coefficient for silver was estimated to be L m/s[Ag] = 100 to 400. We also measured the distributions of the base metals Cu and Ni in the same conditions as the trace elements.

Evaluation of Existing Viscosity Data and Models and Developments of New Viscosity Model for Fully Liquid Slag in the SiO2-Al2O3-CaO-MgO System

Metallurgical properties of slag are determined to a great extent by its viscosity. High-temperature viscosity measurements are time-consuming and expensive. It is necessary to develop an accurate viscosity model for blast furnace slag in the SiO2-Al2O3-CaO-MgO system using reliable viscosity data. This paper describes a systemic evaluation procedure to determine the viscosity data to be used for model development. 1780 viscosity data from 10 to 65 wt pct SiO2, 3.5 to 40 wt pct Al2O3, 2 to 60 wt pct CaO, and 2 to 38 wt pct MgO in the SiO2-Al2O3-CaO-MgO system have been accepted for model evaluation after critical reviews. The existing 14 viscosity models in SiO2-Al2O3-CaO-MgO system is also reviewed and evaluated. Based on the structure of alumina-silicate slag and evaluated viscosity data, a new viscosity model has been proposed for the system SiO2-Al2O3-CaO-MgO. A new term “probability,” based on the basic oxide and electronegativity, is introduced to calculate the integral activation energy of slag. The model has been evaluated and compared with existing viscosity models in three different composition ranges in SiO2-Al2O3-CaO-MgO system for different applications. The new model reports an outstanding agreement between predictions and experimental data. The industrial implications of the new model have also been discussed in ironmaking and steelmaking processes.

Crystallization Behavior of the CaO-Al2O3-MgO System Studied with a Confocal Laser Scanning Microscope

The crystallization behavior of a calcium-aluminate system with various MgO content from 2.5 to 7.5 wt pct and CaO/Al2O3 ratios between 0.8 and 1.2 has been examined using a confocal laser scanning microscope (CLSM). CCT (continuous cooling transformation) and time temperature transformation (TTT) diagrams were constructed to identify the primary crystal phase of slag at different compositions and at cooling rates between 25 and 800 K/minutes. In the slag at a CaO/Al2O3 ratio of 1.0, crystallization temperature increased during isothermal and continuous cooling with higher MgO content, and the shortest incubation time was observed at 5 wt pct MgO. When MgO content was fixed to be 5 wt pct, crystallization temperature increased with lower CaO/Al2O3 ratio. According to the slag composition, cooling rates and temperature, the primary phase could be CA, or C5A3, or C3A, or C3MA2, or MgO, and the crystal morphology changes from dendrites to faceted crystals to columnar crystals in this composition range.

Effect of MgO on Liquidus Temperatures in the ZnO-“FeO”-Al2O3-CaO-SiO2-MgO System in Equilibrium with Metallic Iron

The phase equilibria in the ZnO-“FeO”-Al2O3-CaO-SiO2-MgO system have been determined experimentally in equilibrium with metallic iron. Synthetic slags were equilibrated at a high temperature, quenched, and then the compositions of the phases in equilibrium were measured using electron probe X-ray microanalysis. Pseudoternary sections of the form ZnO-“FeO”-(Al2O3 + CaO + SiO2) for CaO/SiO2 = 0.71, (CaO + SiO2)/Al2O3 = 5 and fixed MgO concentrations of 2, 4, and 6 wt pct have been constructed. Wustite (Fe2+,Mg,Zn)O and spinel (Fe2+,Mg,Zn)O·(Al,Fe3+)2O3 are the major primary phases in the temperature and composition ranges investigated. The liquidus temperatures are increased by 140 K in the wustite primary phase field and by 70 K in the spinel primary phase field with the addition of 6 wt pct MgO in the slag. The partitioning of MgO and ZnO between the solid and liquid phases has been discussed.

Investigation of Liquidus Temperatures and Phase Equilibria of Copper Smelting Slags in the FeO-Fe2O3-SiO2-CaO-MgO-Al2O3 System at PO2 10−8 atm

Copper concentrates and fluxes can contain variable levels of SiO2, CaO, and MgO in addition to main components Cu, Fe, and S. Metal recovery, slag tapping, and furnace wall integrity all are dependent on phase equilibria and other properties of the phases and are functions of slag composition and operational temperature. Optimal control of the slag chemistry in the copper smelting, therefore, is essential for high recovery and productivity; this, in turn, requires detailed knowledge of the slag phase equilibria. The present work provides new phase equilibrium experimental data in the FeO-Fe2O3-SiO2-CaO-MgO-Al2O3 system at oxygen partial pressure of 10−8 atm within the range of temperatures and compositions directly relevant to copper smelting. For the range of conditions relevant to the Kennecott Utah Copper (South Magna, UT) smelting furnace, it was confirmed experimentally that increasing concentrations of MgO or CaO resulted in significant decreases of the tridymite liquidus temperature and in changes in the position of the tridymite liquidus in the direction of higher silica concentration; in contrast, the spinel liquidus temperatures increase significantly with the increase of MgO or CaO. Olivine and clinopyroxene precipitates appeared at high MgO concentrations in the liquid slag. The liquidus temperature in the spinel primary phase field was expressed as a linear function of 1/(wt pctFe/wt pctSiO2), wt pctCaO, wt pctMgO, and wt pctAl2O3. The positions of each of the liquidus points (wt pctFe)/(wt pctSiO2) at a fixed temperatures in the tridymite primary phase field were expressed as linear functions of wt pctCaO, wt pctMgO, and wt pctAl2O3.

Phase equilibrium and minor-element distribution between Ni3S2-FeS matte and calcium ferrite slag under high partial pressures of SO2

Calcium ferrite slag has been successfully used in the copper smelting process, but no attempt has been made to use it in the nickel smelting process. The phase equilibrium and the distribution of minor elements between the Ni3S2-FeS matte and the CaO-FeOx-based slag (containing about 2 wt pct MgO) in a magnesia crucible were investigated at 1523 K under controlled partial pressures of S2, O2, and SO2 of 10.1, 50.7, and 101.3 kPa, respectively. The results were compared with those for the iron-silicate-based slag, and the following conclusions were obtained: (1) there is no significant difference in the solubility of nickel between both slags in the high-matte-grade range, (2) the dissolution of cobalt in the calcium ferrite slag is clearly smaller than that in the iron silicate slag, (3) detrimental arsenic, antimony, and bismuth are preferentially collected and fixed in the calcium ferrite slag rather than in the iron silicate slag, and (4) it is considered, with regard to technical feasibility, that the use of the calcium ferrite slag in a converting process of the Bessemer matte will have a prominent future for the nickel converting stage.

Phase equilibrium and minor element distribution between FeO x -SiO2-MgO-based slag and Cu2S-FeS matte at 1573 K under high partial pressures of SO2

As part of a fundamental study of copper smelting processes using oxygen or oxygen-enriched air as a blowing gas, phase equilibrium and distribution of minor elements between copper matte and SiO2-saturated FeOx-SiO2-MgO-based slag containing 5 to 10 wt pct MgO have been investigated at 1573 K under the SO2 partial pressures of 10.1, 50.7, and 101.3 kPa. The copper and sulfur solubilities in the slag were found to be independent of \(p_{SO_2 } \) when the matte grade was specified, and this behavior was ascribed to the constancy of \(\left( {{{p_{O_2 } } \mathord{\left/ {\vphantom {{p_{O_2 } } {p_{S_2 } }}} \right. \kern-\nulldelimiterspace} {p_{S_2 } }}} \right)\) against \(p_{SO_2 } \) at a given matte grade. When the distribution ratio of a minor element (X) between the slag and matte phases was defined as Lxs/m=(wt pct X in slag)/{wt pct X in matter}, Lxs/m for arsenic, antimony, and bismuth at a given matte grade increased with increasing \(p_{SO_2 } \). On the other hand, the distribution ratio of silver at a given matte grade was almost constant against \(p_{SO_2 } \).

Distribution of antimony between carbon-saturated iron and synthetic slags

In order to develop an understanding of the behavior of Sb in the blast furnace, the distribution of antimony between carbon-saturated iron and synthetic slags of CaO-MgO-SiO 2 -Al 2 O 3 has been investigated. The experiments were conducted at 1450°C, 1500°C, and 1550°C and at slag basicities [(wt pct CaO + wt pct MgO)/(wt pct SiO 2 + wt pct Al 2 O 3 )] of 0.666, 0.818, and 1.00. Those values correspond to silicate degrees of 2.37, 2.01, and 1.74, respectively

Faceted-nonfaceted dendritic transitions during the laser processing of Al2O3-1.0 Wt Pct MgO

Faceted-nonfaceted dendritic transitions during the laser processing of Al2O3-1.0 Wt Pct MgO

Chemistry, microstructure, and reduction characteristics of dolomite-fluxed magnetite pellets

The addition of dolomite to iron ore pellets improves high temperature reduction properties, primarily by increasing their softening point and reducibility. This study was made to ascertain the compositional ranges within which dolomite fluxed magnetite pellets show such an improvement over good acid pellets. A variety of compositions with MgO levels from 1 to 2 wt pct and CaO/SiO2 ratios of 0.6 to 1.8 were prepared using Hibbing magnetic concentrate. These compositions were balled and then pot-grate fired to various temperatures. Petrographic examination and electron microprobe analyses were used to characterize the phase assemblages. Reduction characteristics were also evaluated. As evidenced by the following petrographically observed relationships, the CaO/SiO2 ratio (c/S) was found to be the controlling factor for pellet microstructure: a) The low c/S ( 1.3) pellets were mostly calcium ferrite-bonded. Intermediate c/S compositions contain more magnesioferrite than do either low or high basicity compositions. Pellets must be fired to a high enough temperature to generate sufficient liquid for ion transport but not so high as to cause pellets to stick together. Well-fired pellets with a c/S of 1.3 or less performed adequately in low temperature degradation tests. Pellets with a c/S of 0.8 or greater displayed satisfactory swelling behavior. Therefore, we determined that pellets within a c/S range of 0.8 to 1.3 are technically acceptable. Pellets containing 1.5 wt pct MgO had the best reduction characteristics, but all fluxed compositions reduced faster and more completely than did acid pellets. Increasing MgO content up to 2.0 pct increased the softening temperature by 165‡C over acid pellets. On the basis of pellet test results and taking into consideration the auxiliary influence of economic and operating considerations, we determined the optimum composition of dolomite fluxed Hibbing pellets to be 1.5 pct MgO and a C/S of 0.8.

Kinetics of chromium oxide reduction from a basic steelmaking slag by silicon dissolved in liquid iron

The reduction of chromium oxide from a basic steelmaking slag (45 wt pct CaO, 35 wt pct SiO2, 10 wt pct MgO, 10 wt pct A12O3) by silicon dissolved in liquid iron at steelmaking temperatures was studied to determine the rate-limiting steps. The reduction is described by the reactions: (Cr2O3) + Si = (SiO2) + (CrO) + Cr [1] and 2 (CrO) +Si = (SiO2) + 2 Cr [2] The experiments were carried out under an argon atmosphere in a vertical resistance-heated tube furnace. The slag and metal phases were held in zirconia crucibles. The course of the reactions was followed by periodically sampling the slag phase and analyzing for total chromium, divalent chromium, and iron. Results obtained by varying stirring rate, temperature, and composition defined the rate-limiting mechanism for each reaction. The rate of reduction of trivalent chromium (reaction [1] above) increases with moderate increases in stirring of the slag, and increases markedly with increases in temperature. The effects of changes in composition identified the rate-limiting step for Cr+3 reduction as diffusion of Cr+3 from the bulk slag to the slag-metal interface. The rate of reduction of divalent chromium does not vary with changes in stirring of the slag, but increases in temperature markedly increase the reaction rate. Thus, this reaction is limited by the rate of an interfacial chemical reaction. The reduction of divalent chromium is linearly dependent on concentration of divalent chromium, but is independent of silicon content of the metal phase.