Investigations on the carbothermic reduction of chromite ores

Experimental studies were carried out on the reducibility of two different chromite ores using different reducing carbonaceous reducing agents in the temperature range 1173 to 1573 K. “Friable lumpy” ores and “hard lumpy” ores were used in the experiments. Petroleum coke, devolatilized coke, (DVC) and graphite were used as reducing agents. It was found that iron was practically completely reduced before the commencement of the reduction of chromium in the ore. The reduction of iron was controlled by diffusion. The activation energy for this process was estimated to be 130 kJ/mole. The reduction of chromium was controlled by either chemical reaction or nucleation. Rate of reduction was highest when raw petroleum coke was used as the reducing agent. The DVC was less effective compared to raw coke, whereas the rate of reduction was lowest when graphite was used as the reducing agent.     

Kinetics and mechanism of carbothermic reduction of magnesia

The reaction between MgO and graphite powders under flowing argon atmosphere was studied using a dynamic thermogravimetric method. In the temperature range 293 to 1973 K, the effects of compacting pressure, magnesia/carbon ratio, heating rate, Ar carrier-gas flow rate, and CO-partial pressure were investigated. An experimentally determined reaction mechanism was proposed and discussed. The reduction process could be divided into two stages. The first stage includes the direct reaction between MgO and graphite particles and partial gas-solid reaction at relatively low temperature (below 1750 K). The overall reaction rate depends on the solid phase-boundary reaction between magnesia and carbon particles. The second stage is the gas-solid reaction between CO and MgO, which determines the overall reaction rate. The apparent activation energies of the two stages were estimated to be 208.29 and 374.13 kJ/mol, respectively.     

微细粒贫赤铁矿碳热还原的动力学

通过对微细粒贫赤铁矿进行非等温动力学研究,考察其反应控速环节,并探究反应配碳量及升温速率对还原过程的影响,研究结果表明:还原过程由界面反应控制;配碳量增加及升温速率提高均对还原反应起促进作用;碱金属盐对还原具有催化作用,降低了反应活化能。     

Kinetics of manganese ore reduction by carbon monoxide

A step has been made in the direction of understanding the fundamental chemical processes taking place inside electric are furnaces producing manganese alloys. The reduction of higher manganese oxides to MnO by carbon monoxide has been studied in the temperature range 700 °C to 1100 °C. A topochemical pattern with a single shrinking core inside the ore particles has been observed in most cases. It has been found that the reduction of some manganese silicates (braunite minerals) is influenced by reaction interface kinetics, whereas the reduction rate of manganese oxides (bixbyite and hausmannite) is mostly determined by product shell pore diffusion. Sintering kinetics and the extent of natural porosity determine the product shell pore diffusivity. As the melting point of the reaction product is approached, rapid sintering leads to a decrease in diffusivity.     

钒钛磁铁矿固态直接还原的动力学研究

在温度为1 100~1 350℃及惰性气体保护条件下,对钒钛磁铁矿进行了等温直接还原试验,研究了还原温度、时间等还原条件对还原速率和金属化率的影响。结果表明:在温度为1 150~1 350℃时,初始30 min的还原速率高,之后还原缓慢;动力学分析结果表明,在温度1 100~1 350℃,钒钛磁铁矿内配碳直接还原反应受三维扩散控制。     

Studies in the carbothermic reduction of phosphogypsum

Phosphogypsum has been reduced in the solid state by active charcoal both in the presence and absence of catalysts. Kinetic data could be fitted to the modified volume reaction model. Mixed catalysts like potassium dichromate were found to enhance the reaction rate quite satisfactorily. This result could be fruitfully employed during reduction with industrial coke also.     

Mechanically activated carbothermic reduction of ilmenite

A systematic study of the effect of milling conditions on the low-temperature carbothermic reduction of the mineral ilmenite has been carried out. It was found that after ball milling of an ilmenite-carbon mixture at room temperature, the ilmenite was reduced to rutile and metallic iron during subsequent low-temperature annealing (760 °C for 30 minutes). A longer milling time results in a lower reduction temperature and a higher reduction rate. Higher milling intensity also leads to a lower reduction temperature. This enhanced reduction reaction induced by ball milling mainly results from the intimate mixing and large contact area between milled ilmenite and carbon particles.     

Phase formation during the carbothermic reduction of eudialyte concentrate

The phase transformations of eudialyte concentrate during the carbothermic reduction in the temperature range 25–2000°C are studied by thermodynamic simulation, differential thermal analysis, and X-ray diffraction. As the temperature increases to 1500°C, the following phases are found to form sequentially: iron and manganese carbides, free iron, niobium carbide, iron silicides, silicon and titanium carbides, and free silicon. Strontium, yttrium, and uranium in the temperature range under study are not reduced and are retained in an oxide form, and insignificant reduction of zirconium oxides with the formation of carbide ZrC is possible only at temperatures above 1500°C.     

Physicochemical aspects of carbothermic reduction of cassiterite in the ionic melt

Conditions of the carbothermic reduction of the cassiterite concentrate in the melt of the Na₂CO₃-NaNO₃ salt system (weight ratio 1: 0.3) are investigated. The charge composition is established, and the temperature range of reduction (600–900°C) is determined. It is shown that the intermediate Na₂SnO₃ compound is formed during the interaction of cassiterite with the melt. This compound is mainly reduced by gaseous CO in a liquid phase of the melt with a high rate (1.5 h), thereby providing the recovery of 97% Sn from the cassiterite concentrate into the crude alloy.     

Kinetics of manganese reduction leaching from weathered rare-earth mud with sodium sulfite

The kinetics of manganese reduction leaching in an acidic medium from a weathered rare-earth mud (WREM) were investigated. Using sodium sulfite as a reductant, the effect of reaction temperature, mechanical agitation rate, sulfuric acid dosage, and feed particle size on leaching kinetics were examined. The leaching process can be described by the shrinking-core model. An apparent activation energy of 11.5 kJ/mol for manganese reduction leaching is estimated. The diffusion of reactants and leaching products through a porous ore matrix was found to be the rate-limiting step. An empirical equation relating the manganese leaching rate constant with feed-particle size and leaching temperature was established. It was found that the smaller the feed-particle size or the higher the leaching temperature, the faster the leaching proceeds, as anticipated. The kinetic process exhibited a self-catalysis characteristic of Mn²⁺ in the mud. This finding suggests that Mn(III,IV) in the mud was rapidly reduced to Mn²⁺ during the initial stage of leaching.     

Gaseous reduction of laterite ores

Lateritic nickel ores have been reduced under laboratory conditions. The reduction experiments were carried out at temperatures from 500 °C to 1100 °C in a horizontal tube furnace using various mixtures of H₂ and CO₂. The hydrogen evolution method was used to measure the degree of metallization of the reduced ore. It was found that the rate of reduction was very low at 500 °C but then increased rapidly upon heating the ore to 600 °C. The percent metallics increased with increasing H₂ to CO₂ ratios in the reducing gas. At temperatures between 600 °C and 1100 °C, a H₂ to CO₂ ratio of 3 leads to the formation of 5 to 6 pct metallics in the reduced calcine was shown. Heating the ore in air or nitrogen prior to reduction does not affect the degree of metallization. A H₂ to CO₂ ratio of at least 4 is required to obtain a ferronickel product analyzing 36 pct nickel if no further reduction is carried out during the subsequent smelting operation.     

Solid-phase carbothermic reduction of the components of chrome-iron ore raw materials

The procedure and results of laboratory studies of the solid-phase reduction of chromium and iron from chrome-iron ore raw materials are presented.     

Kinetic study on carbothermic reduction of MnO2 with graphite

The carbothermic reduction of MnO₂ with graphite has been investigated for the reduction mechanism in the temperature range of 1000–1300°C. Although several researchers studied the reduction step from MnO₂ to MnO, it was attempted to employ the in situ testing of reduction behaviour with the analysis of product gas composition simultaneously from the different points of view. The overall reduction rate increased with temperature, which was controlled by the carbon gasification. It is because the reduction rate of MnO₂ to MnO was much faster than the carbon gasification at the experimental temperatures. This was confirmed by the generation of negligible amount of CO compared with CO₂ in the analysis of product gases. Furthermore, the results could explain the difficult formation of manganese carbide from MnO₂ in contrast with the carbide formation from pure MnO.     

Kinetics of manganese oxide reduction from basic slags by carbon dissolved in liquid iron

The reduction of manganese oxide from a basic slag by carbon dissolved in liquid iron is a slow reaction, failing to approach equilibrium closely in 20 hr. Furthermore, the rate of stirring has no apparent effect on the reaction rate. This identifies the rate-controlling step as a chemical reaction at the interface. Only the model for the reactionO ²⁻ =O + 2e ⁻ gave a consistent interpretation as the melt geometry, and concentration of manganese oxide and carbon were varied. The rate constant for this reaction was found to be 1.28 × 10⁻⁵ mole per sq cm per min at 155O°C. The effect of temperature is substantial with a calculated energy of activation for the system of 25 kcal per mole. Formerly Graduate Student, The University of Michigan This paper is based on a portion of a thesis submitted by W. L. DAINES in partial fulfillment of the requirements for the degree Doctor of Philosophy at The University of Michigan.     

含锌电炉粉尘水浸处理-真空碳热还原工艺

根据国家对绿色冶金的倡导,对如何高效无污染回收含锌电炉粉尘中的金属锌及K、Na元素进行研究,采用水浸预处理回收粉尘中K、Na元素,再进行真空碳热还原回收金属锌。试验结果表明,水浸最佳方案为固液比为1∶10(g/ml)、搅拌速度为300 r/min、水浸时间为70 min。此条件下,K元素浸出率达91.09%,Na元素浸出率达85.68%。通过FactSage 8.0软件模拟真空碳热还原电炉粉尘在不同含碳条件下热力学行为,并结合前期探索试验表明,水浸渣添加质量分数为10%的焦炭、还原温度为950℃、保温时间为60 min的条件下进行真空碳热还原试验可有效分离Fe、Zn元素,获得金属锌锭(Zn质量分数为98.15%)及高品质铁精粉(Fe质量分数为61.93%)。     

Calculations of manganese ferroalloys production efficiency from different ores

The cost of producing manganese alloys by reduction from manganese ore using carbothermic process is estimated. Alternatives of FeMn78 and SiMn17 production from rich Australian manganese ore with low-phosphorus concentration or low-phosphorus manganese slag in charge mixture with poor domestic Russian ore with comparatively high phosphorus content are calculated and presented in the article. Direct production costs for alternative variants in a wide range of cherge composition are estimated.     

Influence of pellet composition and structure on carbothermic reduction of silica

The melting zone in a cupola has temperatures greater than 1773 K and a reducing atmosphere. This condition is suitable for the carbothermic reduction of silica. The key to the applicability of carbothermic reduction of silica for ferroalloy production is rapid in situ production of SiC and its subsequent dissolution in the hot metal. The main objective of this investigation was to study the kinetics of the carbothermic reduction process and determine the optimum parameters for rapid and complete in situ conversion of silica to SiC. At temperatures above 1773 K, the key reactions in the carbothermic reduction process are (1) SiO₂ (s)+CO (g)=SiO (g)+CO₂ (g), (2) SiO (g)+2C (s)=SiC (s)+CO (g), (3) C (s)+CO₂ (g)=2CO (g). To meet the objective of this study, conditions must be such that the surface reactions occurring at the carbon and silica surfaces are rate limiting and the entire silica is converted to SiC. Pellet composition and structure in terms of carbon to silica ratio, their particle sizes, and compaction pressure that ensure surface reaction is rate controlling were determined. The gas-solid reaction kinetics was mathematically modeled in terms of the process parameters. The reaction kinetics improved by reducing both carbon and silica particle sizes. However, below a certain critical particle size, there was no significant improvement in the reaction kinetics. For complete conversion of SiO₂ (s) to SiC (s), excess carbon and critical porosity are necessary to ensure that the entire SiO (g) generated by Reaction [1] is consumed via Reaction [2] within the pellet.