Design and Fabrication of Pellets for Magnesium Production by Carbothermal Reduction

For carbothermal reduction (CTR) to be an economic and clean process for magnesium metal production, operational challenges must be overcome. Strong and reactive precursor pellets are necessary to effectively and selectively produce Mg_(g) from any feedstock. In this study, the effects of ore (magnesia and dolime), carbon (petroleum coke, charcoal, algal char, and carbon black), and binder (organic and inorganic) on pellet strength and reactivity, product yield and purity, and reduction selectivity were analyzed. Theoretically and experimentally, the CTR of dolime (MgO·CaO) favored MgO reduction over CaO reduction; however, with enough carbon and heat, both oxides could be reduced. CaO carbothermal reduction produced CaC₂ and Ca_(g). The selectivity to CaC₂ remained constant (7 ± 4 pct) for all C/MgO·CaO ratios analyzed, while the selectivity to Ca_(g) increased (5 pct → 40 pct) when C/MgO·CaO was increased from 0.5 to 2.0. As the overall metal yield decreased (77.6 pct → 59.7 pct) with increasing CaO reduction (38.2 pct → 78.1 pct), Ca_(g) reverted faster than Mg_(g). Heavy metal impurities primarily remained in the residue (< 30 pct volatilized) and, when volatilized, condensed at high temperatures (700 °C to 1450 °C), relative to light metal impurities (350 °C to 1000 °C, > 78 pct volatilized). Organic binders added reducing power to the pellets but produced frail pellets (radial crush strength = 9.1 ± 0.7 N) after pyrolysis, relative to pellets with inorganic binders (15.1 ± 3.2 N). Kinetic parameters were determined for extruded pellets to predict the reaction rate as a continuous function of pressure and temperature.     

Studies on dissolution kinetics of dolime in electrothermal magnesium slag

The electrothermal process of magnesium metal production is a promising route, where large sized internally heated reactor is used for magnesium production resulting in less energy and labour intensive and high space-time yield process. However, the dissolution behavior of dolime in the electrothermal slag has been found critical for the process optimization. In this paper, the dissolution kinetics of the dolime in the slag was discussed. Quaternary slag (CaO-Al₂O₃-SiO₂-MgO) was prepared having basicity CaO/SiO₂ ≥ 1.8 and Al₂O₃/SiO₂ ≥ 0.26 for dolime dissolution studies by static hot dip method. Prior to the experiments, FactSage calculations were carried out varying temperatures and slag compositions. In the kinetic studies, dolime particles 10–15 mm size was added in slag melted at 1450, 1500 and 1550°C and samples were taken at various time intervals. The chemical analysis of slag sample was carried out to investigate the dissolution kinetics to establish the rate expression. The activation energy for the process was calculated for different models used in study and was found to be in the range of 130–270 kJ/mol. SEM analysis was done for surface analysis of reacted particles. This study would be helpful in optimizing the dolime charging rate during pilot scale trials for electrothermal magnesium production at CSIR-NML, Jamshedpur.     

对煅白表面改性提高出镁率

主要介绍了生产煅白的工艺参数,并对煅白的表面改性及其表征方法进行了分析。     

Thermochemical Analysis of Phases Formed at the Interface of a Mg alloy-Ni-plated Steel Joint during Laser Brazing

The thermodynamic stability of precipitated phases at the steel-Ni-Mg alloy interface during laser brazing of Ni-plated steel to AZ31B magnesium sheet using AZ92 magnesium alloy filler wire has been evaluated using FactSage thermochemical software. Assuming local chemical equilibrium at the interface, the chemical activity–temperature–composition relationships of intermetallic compounds that might form in the steel-Ni interlayer-AZ92 magnesium alloy system in the temperature range of 873 K to 1373 K (600 °C to 1100 °C) were estimated using the Equilib module of FactSage. The results provided better understanding of the phases that might form at the interface of the dissimilar metal joints during the laser brazing process. The addition of a Ni interlayer between the steel and the Mg brazing alloy was predicted to result in the formation of the AlNi, Mg₂Ni, and Al₃Ni₂ intermetallic compounds at the interface, depending on the local maximum temperature. This was confirmed experimentally by laser brazing of Ni electro-plated steel to AZ31B-H24 magnesium alloy using AZ92 magnesium alloy filler wire. As predicted, the formation of just AlNi and Mg₂Ni from a monotectic and eutectic reaction, respectively, was observed near the interface.     

A new energy-efficient and environmentally friendly process to produce magnesium

A new process for magnesium production was proposed in which both the calcination stage and the reduction stage are performed in one retort. Thermal analysis and vacuum reduction experiments were carried out for evaluating the feasibility of the process. The results suggested that ferrosilicon and CaF₂ reduced the decomposition temperature of dolomite in the pre-prepared pellets, which was approximately 40?K lower than that of pure dolomite pellet. The reduction ratio larger than 90% was obtained at 1573?K for 3?h in the process. The element Fe may not participate in the reduction reactions, which were caused by the diffusion of Si. Magnesium sheet with a high crystallinity and magnesium powder containing a small amount of magnesia were obtained from the present experiments.     

Equilibria in the silicothermic reduction of calcined dolomite

When a mixture of calcium oxide and silicon is heated to above 1000°C a liquid Ca-Si alloy is formed. When magnesium metal is produced by reacting calcined dolomite with silicon, the alloy still forms and is the effective reducing agent for magnesium oxide. In this investigation the thermodynamic data on the Ca-Si alloys have been related to the magnesiumproducing reaction, the calcium pressures over mixtures CaO + Si were measured using a Knudsen cell, and the magnesiumand calcium pressures over the mixtures CaO + MgO + Si were measured using the transportation method. The magnesium content of the equilibrium alloy was determined isopiestically and the identity of the silicate was established. The results constitute a complete and consistent definition of the equilibria in the magnesium production reaction, and have also yielded an improved value of thefree energy of formation of calcium orthosilicate. Formerly Graduate Student, University of Toronto, Toronto, Ontario, Canada.     

Effect of Microwave Treatment Upon Processing Oolitic High Phosphorus Iron Ore for Phosphorus Removal

Influence of microwave treatment on the previously proposed phosphorus removal process of oolitic high phosphorus iron ore (gaseous reduction followed by melting separation) has been studied. Microwave treatment was carried out using a high-temperature microwave reactor (Model: MS-WH). Untreated ore fines and microwaved ore fines were then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and thermogravimetric analysis (TGA). Thereafter, experiments on the proposed phosphorus removal process were conducted to examine the effect of microwave treatment. Results show that microwave treatment could change the microstructure of the ore fines and has an intensification effect on its gaseous reduction by reducing gas internal resistance, increasing chemical reaction rate and postponing the occurrence of sintering. Results of gaseous reduction tests using tubular furnace indicate both microwave treatment and high reduction temperature high as 1273 K (1000 °C) are needed to totally break down the dense oolite and metallization rate of the ore fines treated using microwave power of 450 W could reach 90 pct under 1273 K (1000 °C) and for 2 hours. Results of melting separation tests of the reduced ore fines with a metallization rate of 90 pct show that, in addition to the melting conditions in our previous studies, introducing 3 pct Na₂CO₃ to the highly reduced ore fines is necessary, and metal recovery rate and phosphorus content of metal could reach 83 pct and 0.31 mass pct, respectively.     

Vacuum Carbothermic Reduction of Panzhihua Ilmenite Concentrate: A Thermodynamic Study

Electric arc furnace is mainly used in the production of high titania slag; however, since impurities cannot be eliminated, this causes difficulty in the production of titania pigment with chlorination process. Consequently, removing impurities is the crucial way to deal with low-grade ilmenite, especially for the Panzhihua ilmenite concentrate in China. This article studied the theoretical calculation of vacuum carbothermic reduction of Panzhihua ilmenite concentrate. Thus, when the temperature was higher than 1600°C and the carbon amount was greater than 12%, all of the Fe almost entered into the gas phase. When the temperature was higher than 1300°C and the carbon amount was greater than 14%, magnesium also entered the gas phase. When the temperature was higher than 1100°C, most of the element manganese was volatilized in the gas phase. The TiO₂ grade increased with the increase in carbon amount (14%). When the temperature was higher than 1600°C and the carbon amount was less than 14%, the TiO₂ grade in the slag phase could reach the maximum value, which can be used for the chlorination process to prepare titanium dioxide.     

某难处理金矿石工艺矿物学研究

为探索某金矿石特性,采用BPMA自动测试系统、显微镜、化学分析等技术手段,对其开展了详细的工艺矿物学研究,查明矿石矿物组成、主要矿物嵌布特征等,并分析了影响金、银回收的矿物学因素。结果表明:该矿石为高硫、高砷、高钙难处理金矿石,金品位为6.62 g/t、银品位为58.90 g/t;金属矿物主要有黄铁矿、毒砂,多呈粗—中粒嵌布,少部分呈细粒嵌布;脉石矿物主要有方解石、白云石;金主要为硫化物包裹金,占88.50%,自然金和少量银金矿粒度较细,对金的回收有一定影响;银的独立矿物粒度一般小于0.020 mm,是影响银回收的主要原因。工艺矿物学研究结果为该矿石资源的开发利用提供了参考依据。     

Green metallurgical processing of chromite

A new green metallurgical process for chromite ore has been proposed and developed to solve the serious environmental problem in the traditional production process of chromate. In the new process, the oxidation of chromite ore is carried out in sub-molten potassium hydroxide at 300 °C. Compared with the traditional roasting process in a rotary kiln at 1200 °C, the oxidation and mass transfer are greatly intensified in the new process. Chemical conversion of chromium is above 99% and the recovery of chromium is raised by more than 20% while the reaction temperature is dropped by 900 °C. Thus the energy consumption is decreased. Furthermore, as no limestone or dolomite additives are required, the amount of chromium-containing residue is decreased from 2.5 tonnes to 0.5 tonnes with the production of 1.0 tonne of product in the new process. As all reactions and separating operations are performed in liquid media, pollution due to toxic dust is prevented.With the change of reaction medium, the new process achieves higher resource and energy utilization efficiency. At the same time, the new process also changes the physical and chemical properties of other components co-existing in the chromite ore. The process provides the possibility for virtually complete utilization of chromite and zero emission of residue. Thus, the clean production of chromate can be realized.     

Effect of Lanthanum on Nodule Count and Nodularity of Ductile Iron

The present study aims at finding out the effect of the addition of a single rare earth element, that is, lanthanum on the nodularity and nodule count of ductile iron under controlled conditions. For this purpose, four melts with different compositions were made, using a 28 kg inductotherm medium frequency induction furnace. The temperature was carefully maintained between 1400 and 1450 ℃ for these heats. A good quality charge consisting of Sorel metal, ferrosilicon, Swedish iron, ferrosilicon magnesium, and ferrosilicon lanthanum was used for the production of melts. A vertically parted sand mould was used for casting of 10 test bars made from local silica sand. Standard coin samples were chill-cast to conduct chemical analysis of the ductile iron. Mierostructure study of the samples was conducted using a Leica optical microscope. Nodule count and nodularity of the samples were carried out using an image analyzer. The results obtained indicated that with the increased addition of lanthanum the nodule count of ductile iron increased, thus making it evident that it played a significant role in increasing the mechanical properties. The highest nodule count of 467 was obtained with the addition of 0.03% lanthanum. However, the effect of lanthanum on nodularity was negligible with nodularity ranging from 81% to 83 %.     

Silicon reduction of alkali metal oxides of the type Na2O·Al2O3–xSiO2

Abstract

During the silicothermic production of magnesium from dolomite, alkali metals are produced. Assuming that these metals are present in the ore as complex oxides, the silicon reduction of the mineral nepheline syenite was examined.

This mineral was very resistant to reduction by silicon. At. 1150°C, reaction was 65% complete in seven hours. When MgO and CaO were added, the reaction was 50% complete in two hours. It is suggested that the magnesium gas produced by the reduction of MgO reduces the alkali metal silicate.

Résumé

Au cours de la préparation du magnésium par silicothermie il y a production de métaux du groupe alcalin. En faisant l'hypothese que ces métaux proviennent d'oxydes complexes compris dans le minerai il devenait intéressant d'examiner la réduction de la syénite néphélénique par sillcothermie.

Cette espèce minérale est très refractaire à la réduction par le silicium. A 1150°C la réaction était à 65 p. 100 complétée en sept heures. En présence de MgO et de CaO la réaction était à 50 p. 100 complétée en deux heures. Il semblerait que la vapeur de magnésium provenant de la réduction du MgO réduise le silicate du métal alcalin.     

Utilization of Coke Oven Gas and Converter Gas in the Direct Reduction of Lump Iron Ore

The application of off-gases from the integrated steel plant for the direct reduction of lump iron ore could decrease not only the total production cost but also the energy consumption and CO₂ emissions. The current study investigates the efficiency of reformed coke oven gas (RCOG), original coke oven gas (OCOG), and coke oven gas/basic oxygen furnace gas mixtures (RCOG/BOFG and OCOG/BOFG) in the direct reduction of lump iron ore. The results were compared to that of reformed natural gas (RNG), which is already applied in the commercial direct reduction processes. The reduction of lump ore was carried out at temperatures in the range of 1073 K to 1323 K (800 °C to 1050 °C) to simulate the reduction zone in direct reduction processes. Reflected light microscopy, scanning electron microscopy, and X-ray diffraction analysis were used to characterize the microstructure and the developed phases in the original and reduced lump iron ore. The rate-controlling mechanism of the reduced lump ore was predicted from the calculation of apparent activation energy and the examination of microstructure. At 1073 K to 1323 K (800 °C to 1050 °C), the reduction rate of lump ore was the highest in RCOG followed by OCOG. The reduction rate was found to decrease in the order RCOG > OCOG > RNG > OCOG-BOF > RCOG-BOFG at temperatures 1173 K to 1323 K (900 °C to 1050 °C). The developed fayalite (Fe₂SiO₄), which resulted from the reaction between wüstite and silica, had a significant effect on the reduction process. The reduction rate was increased as H₂ content in the applied gas mixtures increased. The rate-determining step was mainly interfacial chemical reaction with limitation by gaseous diffusion at both initial (20 pct reduction) and moderate (60 pct reduction) stages of reduction. The solid-state diffusion mechanism affected the reduction rate only at moderate stages of reduction.     

Preparation of Industrial Manganese Compound from a Low-Grade Spessartine Ore by Hydrometallurgical Process

The increasing global demands for pure manganese in steel production and manganese compound as dietary additives, fertilizer, pigment, cells and fine chemicals production cannot be over-emphasized. Thus, continuous efforts in developing low cost and eco-friendly route for purifying the manganese ore to meet some defined industrial demands become paramount. Therefore, this study focused on reductive leaching and solvent extraction techniques for the purification of a Nigerian manganese ore containing admixture of spessartine (O_96.00Mn_24.00Al_16.00Si₂₄.₀₀) and quartz (Si_3.00O_6.00). During leaching, parameters such as leachant concentration and reaction temperature on the extent of ore dissolution were examined accordingly for the establishment of extraction conditions. At optimal leaching conditions (1.5 mol/L H₂SO₄?+?0.2 g spent tea, 75 °C), 80.2% of the initial 10 g/L ore reacted within 120 min. The derived dissolution activation energy (Ea) of 35.5 kJ/mol supported the diffusion reaction mechanism. Thus, the leachate at optimal leaching was appropriately treated by alkaline precipitation and solvent extraction techniques using sodium hydroxide and (di-2-ethylhexyl) phosphoric acid (D2EHPA) respectively, to obtain pure manganese solution. The purified solution was further beneficiated to obtain manganese sulphate monohydrate (MnSO₄.H₂O, melting point?=?692.4 °C: 47-304-7403) of high industrial value. The unleached residue (~?19.8%) analyzed by XRD consisted of silicileous impurities (SiO₂) which could serve as an important by-product for some defined industries.     

粗硫酸镍中铁钴钙镁深度脱除的工艺研究

研究了以臭氧和氟化钠为脱杂试剂,采用"溶解造液--强氧化除铁钴--氟化除钙镁--结晶析出"为主干的工艺处理粗硫酸镍,深度脱除其中的铁、钴、钙、镁杂质的工艺可行性及最佳工艺条件。试验结果表明,以臭氧为强氧化剂,可深度脱除粗硫酸镍中的铁钴杂质,最佳反应条件为:反应温度80℃,时间8h,终点pH值4.5~5.0,反应终点溶液中铁、钴浓度小于0.005g/L;以氟化钠做添加剂,可深度脱除粗硫酸镍中的钙镁杂质,最佳反应条件为:反应温度90℃,时间2h,pH值5.5,氟化钠添加系数1.5,反应终点溶液中钙0.007g/L,镁0.005g/L;将"强氧化除铁钴"与"氟化钠除钙镁"工序相结合,可获得更好的除杂效果。     

Calorimetric and fourier transform infrared spectrophotometric studies of potassium elimination by dunite

This report contains the results of simultaneous and comparative differential thermal, thermogravimetric, and Fourier transform infrared spectrophotometric studies of the interaction between K₂CO₃ and a mineral of dunite. The use of olivine during the reduction of iron oxides in the blast furnace is a common practice employed to increase the magnesium content of the slag and to eliminate alkaline elements, principally potassium. However, the use of dunite is less known and can have certain advantages over olivine. In this investigation, a dun ite-coke-K₂CO₃ system was studied to simulate the operating conditions of a furnace in temperatures up to 1200 °C. The results obtained show that the reaction begins with the dehydration of dunite and its transformation into forsterite and enstatite. This is followed by the fusion of potassium carbonate and, at temperatures between 1000 °C and 1200 °C, a series of consecutive chemical reactions that includes the formation of potassium vapor and its reaction with enstatite and clinoenstatite, possiblyvia an intermediate phase in which unstable potassium iron silicates are produced. Ultimately, this leads to the formation of magnesium potassium silicate complexes. In the blast furnace, this silicate would be incorporated into the slag, taking with it the potassium brought in by the coke and iron ore of the load.     

High-Temperature Mechanical Behavior of Extruded Mg-Y-Zn Alloy Containing LPSO Phases

The high-temperature mechanical behavior of extruded Mg_97?3x Y_2x Zn _x (at. pct) alloys is evaluated from 473 K to 673 K (200 °C to 400 °C). The microstructure of the extruded alloys is characterized by Long Period Stacking Ordered structure (LPSO) elongated particles within the magnesium matrix. At low temperature and high strain rates, their creep behavior shows a high stress exponent (n = 11) and high activation energy. Alloys behave as a metal matrix composite where the magnesium matrix transfers part of its load to the LPSO phase. At high-temperature and/or low stresses, creep is controlled by nonbasal dislocation slip. At intermediate and high strain rates at 673 K (400 °C) and at intermediate strain rates between 623 K and 673 K (350 °C and 400 °C), the extruded alloys show superplastic deformation with elongations to failure higher than 200 pct. Cracking of coarse LPSO second-phase particles and their subsequent distribution in the magnesium matrix take place during superplastic deformation, preventing magnesium grain growth.     

Sulfide and sulfate solid solubility in lime,magnesia, and calcined dolomite: Part II. free energy of formation of magnesium sulfate

The free energy of formation of magnesium sulfate and its solubility in magnesia have been determined. The salient feature of the results is that trace amounts of calcium impurity in magnesia noticeably lower the dissociation temperature and pressure of magnesium sulfate. A high-purity magnesia, which was prepared by oxidation of a high-purity magnesium, was used to determine the equilibrium constant for the formation of MgSO₄. The sulfate solubil-ity In magnesia saturated with MgSO₄ was found to be higher than that in lime saturated with CaSO₄. At 1100°C, CaSO₄ and CaS form in calcined dolomite at SO₂ partial pressures higher than those in pure CaO. From these findings it is estimated that at MgO saturation the ac-tivity coefficient relative to CaO is about 0.8.     

Study on Phosphorus Removal of High-Phosphorus Oolitic Hematite by Coal-Based Direct Reduction and Magnetic Separation

In this article, mineralogical phase changes and structural changes of iron oxides and phosphorus-bearing minerals during the direct reduction roasting process were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). It has been found that the reduction of hematite follows the following general pathway: Fe₂O₃ → Fe₃O₄ → FeO → Fe. The last step of the reduction process contains two side reactions: either FeO → Fe₂SiO₄ → Fe or FeO → FeAl₂O₄ → Fe depending on the micro mineralogical makeup of the ore. In the reduction process of FeO → Fe, oolitic structure was destroyed completely and fluorapatite was diffused into gangue while metallic phase is coarsening at temperatures below 1200°C. Therefore, the separation of phosphorus-bearing gangue and metallic iron can be achieved by wet grinding and magnetic separation, and low phosphorus content metallic iron powder can be obtained. However, when the temperature reached 1250°C and beyond, some of the fluorapatite was reduced to elemental P and diffused into the metallic iron phase, making the P content higher in the metallic iron powder.     

Control of autoclave scaling during acid pressure leaching of nickeliferous laterite ore

An operating problem encountered at the Moa Bay operation in Cuba, where nickeliferous laterite ore is processed by sulfuric acid pressure leaching, is the formation of alunite and hematite deposits on the autoclave walls. The AMAX Extractive Research & Development, Inc., metallurgical laboratory (Golden, Colorado) has made substantial improvements in the Moa Bay process in the area of metal recovery, energy consumption, and feed versatility. One of the advantages of AMAX's process is its ability to treat substantial portions of nickel-and magnesium-rich serpentine while maintaining acid utilization efficiency. Scale formation is minimized by combining staged acid addition with vigorous agitation and 270 °C operation. This paper describes how advantage can be taken of MgSO₄· XH₂O precipitation both to inhibit alunite scaling and to disperse hematite scale within the MgSO₄ · XH₂O matrix. Cooling the autoclave from its 270 ·C operating temperature down to 180 ·C takes advantage of the reverse solubility of magnesium sulfate. The magnesium dissolves, liberating entrained hematite, thus providing a means for control of autoclave scale with minimum process disruption. P. B. QUENEAU, Formerly with AMAX Extractive Research and Development, Inc., Golden, CO, P. REY, Formerly with COFREMMI, Paris, France,