Be Thou Exalted, Volume 3: O Lord, By Thee Delivered: Vocal

Pages 1-4 in Be Thou Exalted, Volume 3: Vocal

Impurity removal from Si by Si-Ca-Mg ternary alloying-leaching system

In this work, Si-Ca-Mg alloys were made with different compositions and solidification conditions to investigate the impurity segregation and separation performance from Si, especially for the crucial P impurity at several ppmw levels. Varying acid leaching parameters were also employed to investigate the optimized process window. Results indicate that the novel Si-Ca-Mg alloying-leaching system is valid for high P extraction. The ternary intermetallic phase Ca7Mg7.5±δSi14 appears as the main precipitate in all alloys to gather other minor impurities. Rapid cooling significantly reduced the size of precipitates and Si grain, the impurity segregation was also limited. In the acid leaching experiments, HCl is found as the most economical leaching agents among the studied combinations. Smaller particle size promotes the leaching efficiency, but the increment narrows with increasing Ca/Mg ratio. Leaching kinetics of the studied alloys was found following the modified Kröger-Ziegler model based on a cracking-shrinking mechanism. The impurity purification efficiency increases with increasing Ca/Mg mixing ratio, but significantly reduced by rapid cooling. An analytical model was developed for ternary alloy system to predict the P segregation and its removal with varying alloy concentration through the thermodynamic approach, which shows good agreements of the experimental results.publishedVersio

Magnesiothermic Reduction of Silica: A Machine Learning Study

undamental studies have been carried out experimentally and theoretically on the magnesiothermic reduction of silica with different Mg/SiO2 molar ratios (1–4) in the temperature range of 1073 to 1373 K with different reaction times (10–240 min). Due to the kinetic barriers occurring in metallothermic reductions, the equilibrium relations calculated by the well-known thermochemical software FactSage (version 8.2) and its databanks are not adequate to describe the experimental observations. The unreacted silica core encapsulated by the reduction products can be found in some parts of laboratory samples. However, other parts of samples show that the metallothermic reduction disappears almost completely. Some quartz particles are broken into fine pieces and form many tiny cracks. Magnesium reactants are able to infiltrate the core of silica particles via tiny fracture pathways, thereby enabling the reaction to occur almost completely. The traditional unreacted core model is thus inadequate to represent such complicated reaction schemes. In the present work, an attempt is made to apply a machine learning approach using hybrid datasets in order to describe complex magnesiothermic reductions. In addition to the experimental laboratory data, equilibrium relations calculated by the thermochemical database are also introduced as boundary conditions for the magnesiothermic reductions, assuming a sufficiently long reaction time. The physics-informed Gaussian process machine (GPM) is then developed and used to describe hybrid data, given its advantages when describing small datasets. A composite kernel for the GPM is specifically developed to mitigate the overfitting problems commonly encountered when using generic kernels. Training the physics-informed Gaussian process machine (GPM) with the hybrid dataset results in a regression score of 0.9665. The trained GPM is thus used to predict the effects of Mg-SiO2 mixtures, temperatures, and reaction times on the products of a magnesiothermic reduction, that have not been covered by experiments. Additional experimental validation indicates that the GPM works well for the interpolates of the observations.publishedVersio

Modeling Viscosity of High Titania Slag

TiO2-FeO-Ti2O3 slag system is the dominant system for industrial high-titania slag production. In the present work, viscosities of TiO2-FeO and TiO2-FeO-Ti2O3 systems were experimentally determined using the concentric rotating cylinder method under argon atmosphere. A viscosity model suitable for the TiO2-FeO-Ti2O3 slag system was then established based on the modification of the Vogel-Fulcher-Tammann (VFT) equation. The experimental results indicate that completely melted high-titania slags exhibit very low viscosity of around 0.8 dPa s with negligible dependence on temperature and compositions. However, it increases dramatically with decreasing temperature slightly below the critical temperature. Besides, the increase in FeO content was found to remarkably lower the critical temperature, while the addition of Ti2O3 increases it. The developed model can predict the viscosities of the TiO2-FeO-Ti2O3 and TiO2-FeO systems over wide ranges of compositions and temperatures within experimental uncertainties. The average relative error for the present model calculation is < 18.82 pct, which is better than the previously developed models for silicate slags reported in the literature. An iso-viscosity distribution diagram was made for the TiO2-FeO-Ti2O3 slag system, which can serve as a roadmap for the Ilmenite smelting reduction process as well as the high titania slags tapping process.publishedVersio

Isothermal Hydrogen Reduction of a Lime-Added Bauxite Residue Agglomerate at Elevated Temperatures for Iron and Alumina Recovery

The hydrogen reduction of bauxite residue lime pellets at elevated temperatures was carried out to recover iron and alumina from the bauxite residue in a new process route. Prior to the H2 reduction, oxide pellets were initially prepared via the mixing of an industrial bauxite residue with fine calcite powder followed by calcination and high-temperature sintering. The chemical, compositional, and microstructural properties of both oxide and reduced pellets were studied by advanced characterization techniques. It was found that iron in the oxide pellets is mainly in the form of brownmillerite, and calcium–iron–titanate phases, while upon reduction they are converted to wüstite and shulamitite intermediate phases and further to metallic iron. Moreover, it was found that the reduction at lower temperature of 1000 °C is faster than that at higher temperatures of 1100 °C and 1200 °C. The slower rate and extent of reduction at the higher temperatures is attributed to the porosity loss and reduction mechanism change to a diffusion-controlled process step. In addition, it was found that Al-containing phases in the raw materials are converted mainly to gehlenite in sintered pellets and further to the leachable mayenite phase. The alkaline leaching of selected reduced pellets by a sodium carbonate solution yielded up to 87% Al recovery into the solution, while the metallic iron was not affected.publishedVersio

Elimination of phosphorus vaporizing from molten silicon at finite reduced pressure

对有限负压下熔体硅中磷的挥发去除进行研究。采用电子级硅配制SI-P合金,并采用gd-MS来检测实验前后硅中的磷含量。理论计算结果表明:在有限负压下,硅中的磷以P和P2的气体形式从熔体硅中挥发。实验结果显示:在温度1873k、真空度0.6-0.8PA、熔炼3600S的条件下,熔体硅中的磷从0.046%(460PPMW)下降到0.001%(10PPMW)。实验结果与理论结果一致表明:当熔体硅中磷的含量大且炉腔内气压相对较高时,磷的去除与气压高度相关;而当炉腔气压很低时,磷的去除基本与气压无关。原因是在相对高磷含量的熔体硅中,磷主要以P2气体的形式挥发;在磷含量较低时,磷主要以单原子气体P的形式挥发。Elimination of phosphorus vaporizing from silicon was investigated.Si-P alloy made from electronic grade silicon was used.All the samples were analyzed by GD-MS.Theory calculation determines that phosphorus evaporates from molten silicon as gas species P and P2 at a finite reduced pressure.The experimental results show that phosphorus mass fraction can be decreased from 0.046% (460ppmw) to around 0.001% (10ppmw) under the condition of temperature 1 873 K, chamber pressure 0.6-0.8 Pa, holding time 1 h.Both experimental data and calculation results agree that at high phosphorus concentration, phosphorus removal is quite dependent on high chamber pressure while it becomes independent on low chamber pressure.The reason is that phosphorus evaporates from molten silicon as gas species P2 at a relatively high phosphorus concentration, while gas species P will be dominated in its vapour at low phosphorus content.Project(2007J0012)supportedbytheNaturalScienceFoundationofFujianProvince;China;Project(2007HZ0005-2)supportedbytheKeyTechnologicalProgramofFujianProvince;China;Project(BASIC-10341702)supportedbyNorwegianResearchCounci

A Sustainable Process to Produce Manganese and Its Alloys through Hydrogen and Aluminothermic Reduction

Hydrogen and aluminum were used to produce manganese, aluminum&ndash;manganese (AlMn) and ferromanganese (FeMn) alloys through experimental work, and mass and energy balances. Oxide pellets were made from Mn oxide and CaO powder, followed by pre-reduction by hydrogen. The reduced MnO pellets were then smelted and reduced at elevated temperatures through CaO flux and Al reductant addition, yielding metallic Mn. Changing the amount of the added Al for the aluminothermic reduction, with or without iron addition led to the production of Mn metal, AlMn alloy and FeMn alloy. Mass and energy balances were carried out for three scenarios to produce these metal products with feasible material flows. An integrated process with three main steps is introduced; a pre-reduction unit to pre-reduce Mn ore, a smelting-aluminothermic reduction unit to produce metals from the pre-reduced ore, and a gas treatment unit to do heat recovery and hydrogen looping from the pre-reduction process gas. It is shown that the process is sustainable regarding the valorization of industrial waste and the energy consumptions for Mn and its alloys production via this process are lower than current commercial processes. Ferromanganese production by this process will prevent the emission of about 1.5 t CO2/t metal

Duplex Process to Produce Ferromanganese and Direct Reduced Iron by Natural Gas

The application of natural gas instead of solid carbon to produce ferromanganese is a way forward in sustainable development. Mass and energy balances for an integrated duplex process to produce ferromanganese and direct reduced iron (DRI) by natural gas were studied. The process consists of natural gas injection into molten ferromanganese yielding carbon and hydrogen in which the dissolved carbon into the molten metal bath reduces MnO from a coexisting molten slag that is produced from the smelting of manganese ore. Hydrogen and CO gases reduce solid manganese oxides and iron oxides in the Mn ore to MnO and Fe in the ferromanganese reactor burden. A hot gas with a significant amount of CO and H2 leaves the reactor and is upgraded to a rich CO–H2 gas mixture via methane use in a gas reformer. The obtained highly reducing gas is then used to reduce iron ore in a direct reduction reactor for DRI production, while the DRI reactor process gas is partly looped into the gas reformer and the rest is used in an energy recovery unit for electric power generation for the ferromanganese reactor. It is shown that the presented duplex process is more sustainable than the current commercial ferromanganese production process and its application is accompanied by about 50% less electric energy consumption and about 40% less CO2 emission, excluding the source of electricity

Thermochemical Aspects of Boron and Phosphorus Distribution Between Silicon and BaO-SiO2 and CaO-BaO-SiO2 slags

In the production of solar grade silicon by metallurgical route the distribution of B and P between slags and liquid silicon is the most important key issue. The equilibrium and thermochemistry of reactions between liquid silicon and BaO-SiO2 slags and up to 10% BaO-containing CaO-BaO-SiO2 slags is studied through experimental work and using thermodynamic calculations. It is shown that the distribution coefficient of B (LB) is higher for the CaO-BaO-SiO2 slags than that for BaO-SiO2 slags and it is not significantly affected by temperature and composition changes of the slags. In contrast, the distribution coefficient of P (LP) is higher for BaO-SiO2 slags than that for the CaO-BaO-SiO2 slags, and it is higher at lower temperatures. The chemical activities of the dilute solutions of Ba in liquid silicon, and the dilute solutions of B2O3, P2O5 and BaO in the slags are calculated. Moreover, the reaction mechanisms for B, P, Ba and Ca transport between liquid silicon and the slags are explained