Carbonaceous Reductant Research Articles

Analysis of Different Types of Carbonaceous Reductants and Methods of Slag and Sludge Recovery at Converter Production

Recycling of metal-containing wastes with an iron content of more than 15%, such as slag and sludge from the gas cleaning of converter production, can be used to recover the metal. In order to study the reducing properties of coal sludge, coke breeze (coke), Shubarkol coal, a series of experimental melting of coal sludge briquettes with different contents of the listed carbon-containing materials was carried out. Sludge-coal briquettes were made from converter slag and sludge using hydrated lime as a binder. To determine the necessary parameters for the reduction of the iron-containing element, chemical and technical analyzes were carried out for ash content, moisture content and volatile matter. The choice of the optimal component composition of briquetted mixtures has established that the proportion of the reducing agent in the briquette should not exceed 20...25%, in order to avoid excess carbon, which binds into solid carbide compounds. The share of the reducing agent in the briquette was 15...18%. Chemical analysis of the resulting alloy and slag component pointed out the expediency of using Shubarkol coal as a carbonaceous reducing agent with high reactivity and electrical resistivity

The effect of petrographically determined parameters on reductant reactivity in the production of high-carbon ferromanganese

In pyrometallurgical processes, metal oxides are reduced from molten slag through carbothermic reduction. It is of interest to evaluate the reactivity of the carbonaceous materials towards substances such as slag. Characterization techniques such as coal petrography can provide insight into the influence of feed coal properties and how they potentially dictate reductant performance. This study aimed to compare the petrographically determined organic composition of coal to reductant reactivity. Two South African medium-rank C bituminous coals and one anthracite sample were investigated together with high-carbon ferromanganese industrial slag. The reductant reactivity tests were conducted at 1500°C in a muffle furnace to assess the potential of carbonaceous reductant in reacting with the main slag components. SEM-EDS was applied to understand the extent of MnO (and to a lesser extent, SiO2) reduction from the slag. Coal 2, consisting of a greater proportion of vitrinite (59.5 vol% on a mineral matter-free basis and 54.7 vol% including mineral matter) was the most reactive reductant. The anthracite sample, with the highest inert maceral proportions (71.8 vol% including mineral matter and 76.8 vol% on a mineral matter-free basis), was the least reactive reductant.

A Review on Pyrometallurgical Extraction of Antimony from Primary Resources: Current Practices and Evolving Processes

Antimony is classified as a critical/strategic metal. Its primary production is predominated by China via pyrometallurgical routes such as volatilization roasting—reduction smelting or direct reduction smelting. The performance of most of the pyro-processes is very sensitive to concentrate type and grade. Therefore, technology selection for a greenfield plant is a significant and delicate task to maximize the recovery rate of antimony and subsequently precious metals (PMs), mainly gold, from the concentrates. The current paper reviews the conventional pyrometallurgical processes and technologies that have been practiced for the treatment of antimony concentrates. The blast furnace is the most commonly used technology, mainly because of its adaptability to different feeds and grades and a high recovery rate. In addition, several other more environmentally friendly pyrometallurgical routes, that were recently developed, are reviewed but these are still at laboratory- or pilot-scales. For example, decarbonization of antimony production through the replacement of carbonaceous reductants with hydrogen seems to be feasible, although the process is still at its infancy, and further research and development are necessary for its commercialization. At the end, available refining methods for removal of the most important impurities including arsenic, sulfur, lead, iron, and copper from crude antimony are discussed.

Effects of Briquetting and High Pyrolysis Temperature on Hydrolysis Lignin Char Properties and Reactivity in CO-CO2-N2 Conditions

Carbonaceous reductants for pyrometallurgical applications are usually obtained from fossil-based sources. The most important properties of the reductants greatly depend on the application and the feeding of the reductant into the process. However, the mechanical strength, calorific value, fixed carbon content, and reactivity of the reductant are the properties that usually define the applicability of the reductant for different processes. The reactivity of the biochars is usually high in comparison to metallurgical coke, which may restrict the applicability of the biochar in reduction processes. One cause of the higher reactivity is the higher surface area of the biochars, which can be suppressed with agglomeration treatment, e.g., briquetting. In this work, hydrolysis lignin was used for slow pyrolysis experiments to produce biochars. The biochars were pyrolyzed in briquetted form and in as-received form at various temperatures. The reactivity values of the biochars were tested in dynamic reactivity tests in a CO-CO2-N2 gas atmosphere at temperatures of up to 1350 °C. It was found that the yield of the hydrolysis lignin char only decreased by 3.36 wt% when the pyrolysis temperature was elevated from 600 to 1200 °C, while a decrease in yield of 4.88 wt% occurred when the pyrolysis temperature was elevated from 450 to 600 °C. The mass loss of hydrolysis lignin biochar in the reactivity experiment in CO-CO2-N2 atmosphere was significantly decreased from 79.41 wt% to 56.80 wt% when the hydrolysis lignin was briquetted before the slow pyrolysis process and the temperature of the pyrolysis process was elevated from 600 to 1200 °C. This means that the mass loss of the material was suppressed by 22.61 wt% due to the higher pyrolysis temperature and briquetting process.

Evaluation of the mechanical properties of wood-derived charcoal briquettes for use as a reductant

SYNOPSIS Silicon Smelters consumes more than 80000 t/a of wood-derived charcoal as carbonaceous reductant in the production of silicon metal. More than 10% of this material is discarded as fines (<6 mm) generated due to abrasion during processing. Charcoal fine residues (<650 μm) and polyvinyl alcohol (PVA) binder were used in this study to produce mechanically strong charcoal briquettes for metallurgical application as carbonaceous reductant. The PVA binder was added in mass percentages of 1, 3, and 5 wt% to the charcoal fines. The compressive strength, abrasion resistance index (ARI), drop shatter resistance (SRI), and water resistance index (WRI) were measured as functions of curing for up to 7 days under atmospheric conditions, and the results compared with metallurgical grade coarse charcoal. The ash content of the produced briquettes was found to be high (6.6-8.0%) compared with the coarse charcoal (1-3%). The 3 and 5 wt% PVA-bound briquettes were found to be the strongest, with compressive strengths of 40 and 115 kg/cm2 respectively, with WRI values of 75 and 73% respectively. The produced briquettes were found to have lower ARI and SRI values compared to the coarse charcoal. Future work should include beneficiation of the fine charcoal discards prior to briquetting, and an increase in binder addition to above 6 wt% to improve the ARI and SRIn. Keywords: wood charcoal, fines, briquettes, reductant, polyvinyl alcohol binder, compressive strength, water resistance, curing time.

Effect of AC as a reductant through the coupling treatment of microwave-assisted and alkali carbonate on silicon production

High energy consumption and high pollution arising from the production of a compound reductant with high-coke and high-coal has drawn universal attention and urgently requires a solution. In this study, activated carbon (AC) as a carbonaceous reductant produced via combined microwave heating and additive inclusion (K2CO3 and Na2CO3) was investigated during carbothermic reduction of silicon. The effect of microwave-assisted treatment on the kinetic and thermal behavior of AC mixed with alkali carbonate was evaluated by thermogravimetric analysis. By using microscopy techniques such as Raman spectroscopy, Fourier-transform infrared spectroscopy, and field-emission scanning electron microscopy (FESEM), the influence of specific factors on the chemical properties of the AC were analyzed. The results showed that the properties of the silicon produced via carbothermic reduction changed after microwave-assisted treatment, which was attributable to changes in structure of the aromatic ring and carbon chain in the AC. In the presence of different alkali carbonates, AC subjected to microwave-assisted treatment exhibited varied in performance because of the different degrees of microwave absorption of the different alkali carbonates. For the additive K2CO3, weight loss improved by 54.35%, and activated energy was reduced by 31.32% during reduction reaction under microwave-assisted treatment. Similarly, the weight loss increased by 42.01%, and the activated energy decreased by 14.30% for the additive Na2CO3. These data indicated that the largest improvement was achieved under microwave-assisted treatment, which contributed substantially to energy-saving. Carbonaceous reductants are important raw materials for silicon production, which currently present a major technical problem. These research results may provide new insights into the use of AC loaded with alkali metal compounds as a carbon reducing agent in production systems.

Simultaneous Selective Chlorination and Carbothermic Reduction of High-Iron Manganese Ore for the Recovery of Manganese Chloride and Metallic Iron

Metallurgical processing of low-grade manganese ore with high iron content is gaining increasing attention due to the gradual depletion of high-grade Mn ores, amid the difficulties in its efficient extraction for both Mn and Fe values in an environmentally-friendly manner. Attempting to tackle the difficulties, this paper describes an innovative process for selectively chlorinating and reducing the high-Fe manganese ore in a simultaneous manner, aiming to produce water-soluble MnCl2 and metallic Fe. After pre-mixing with carbonaceous reductant, CaCl2 and MgCl2 as the chlorinating agent, the Mn ore was heated at 1000 °C. As much as 89.4% Mn can be chlorinated in its water-soluble form, with dissolution of only 3.0% Fe. The presence of CaCl2 during carbothermic reduction resulted in significant promotion in both the Fe reduction rate and formation of large metallic Fe particles due to the segregation effect, facilitating subsequent separation. Selective Mn chlorination by MgCl2 took place with or without the involvement of SiO2, forming MgSiO4 or MgO, respectively.

Influence of Temperature on Reaction Mechanism of Ilmenite Ore Smelting for Titanium Production

The carbothermic smelting reduction process of ilmenite ore at high temperature was investigated by thermodynamic calculations in conjunction with smelting experiments. Based on thermodynamic calculations, conducting the smelting process at a higher temperature was recommended to achieve a larger amount of FeO reduction, i.e., higher Ti-enrichment, as less precipitate and thus large amounts of a liquid slag were predicted. However, even though the reduction of FeO in ilmenite ore at the initial stage seemed to be faster as the temperature increased, no significant difference in the TiO2 or FeO concentration was observed after the reaction was complete, regardless of the temperature. This was caused by the precipitation of pseudobrookite due to the local depletion of FeO during reaction at higher temperatures, by which further reduction reaction was prohibited. The apparent rate constant increased with increasing temperature and the activation energy of the reduction process was estimated to be 144 kJ/mol, from which it was concluded that the reduction reaction of FeO in ilmenite slag by carbonaceous reductant was generally controlled through the mass transfer in the slag phase. Additionally, the formation of TiC also occurred in the iron bath. At 1923 K (1650 °C), approx. 20 pct more TiC was generated as compared to TiC formation at 1823 K (1550 °C), which also prevented further reduction of Fe at higher temperatures.

Carbothermic reduction of chromite fluxed with aluminum spent potlining

Abstract Aluminum spent potlining (SPL) was employed as both the fluxing agent and a source of carbonaceous reductant for the carbothermic reduction of chromite, aiming to allow effective separation of alloy from the slag component. The experimental results show that the carbonaceous component of the SPL is more reactive towards chromite reduction compared to graphite. The formation of refractory spinel (MgAl2O4) on chromite particles hinders further reduction and alloy growth. The slag-making components of the SPL (e.g. nepheline and NaF) form molten slags at low temperatures (∼1300 °C) and partly dissolve the refractory spinel as well as the chromite. Destruction of the spinel layer with enhanced mass transfer greatly improves the alloy growth, which can be further promoted by reduction at a higher temperature (e.g. 1500 °C). Ferrochrome alloy particles grow large enough at 1500 °C in the presence of SPL, allowing effective separation from the slag component using elutriation separation.

Silicon Carbide Formation Enhanced by In-Situ-Formed Silicon Nitride: An Approach to Capture Thermal Energy of CO-Rich Off-Gas Combustion

Carbothermic smelting of ores to produce metals or alloys in alternating current open/semiclosed and closed submerged arc furnaces, or in closed direct current furnaces, results in large volumes of CO-rich off-gas being generated. Most of the CO-rich off-gas is cleaned and flared on stacks, since the storing of large volumes is problematic due to the associated toxic and explosive risks. Flaring of CO-rich off-gas results in significant wastage of energy. In this study, an alternative method to partially capture the thermal energy associated with off-gas combustion, in the form of silicon carbide (SiC) generated from waste materials (quartz and anthracite fines), is proposed. SiC can partially replace conventional carbonaceous reductants used to produce alloys such as ferrochromium. The influences of quartz and anthracite particle size, treatment temperature, and gaseous atmosphere (nitrogen or air) on SiC formation were investigated. A quartz-anthracite mixture with 90 pct of the particles < 350.9 µm carbothermically treated at 1873.15 K (1600 °C) resulted in almost complete conversion of quartz to SiC in both nitrogen and air atmospheres. The study indicated significant potential for industrial application of the process.

Efficient and economical recovery of lithium, cobalt, nickel, manganese from cathode scrap of spent lithium-ion batteries

A combined process was presented to recover valuable metals from lithium nickel cobalt manganese (NCM) cathodes of spent lithium-ion batteries. In this process, the cathode scrap was first roasted with carbonaceous reductant, and then carbonation water leaching was employed to selectively extract Li from the roasted cathodes. Finally, the obtained residue was leached in sulfuric acid solution to recover Co, Ni and Mn. A systematic investigation combining thermodynamic analysis, leaching experiments and characterization was conducted to explore the effect of operating conditions and leaching mechanism. The results indicate that the leaching of Li is significantly improved by injecting of CO2 into the leaching system, and more than 80% of Li can be leached within 10 min at a low liquid-solid ratio. High-quality Li2CO3 can be prepared from the leachate by direct evaporation. More than 96% of Ni, Co and Mn are extracted without adding reductant under the conditions of a H2SO4 dosage of 1.15 times the theoretical value, a time of 2.5 h, a temperature of 55 °C and a liquid-solid ratio of 3.5 mL g−1. The acid leaching process is more efficient and economical, which is ascribed to the transformation of the low-valence states of metals with high activity after reduction roasting.

Smelting of ferrosilicum from the position of energy and technology criteria of ferroalloys electric arc furnace operation

For estimation of ferroalloy-producing electric arc furnace operation efficiency an energy and technology criteria proposed. Its physical meaning is as follows: it determines a share of energy from the current source, in particular its useful part, spent by ore reduction carbon-thermal process of a ferroalloy production (ferrosilicum, ferrochrome, ferromanganeese), taking into account heat losses and degree of extraction of the leading element into the alloy.Results of an analysis of ferroalloys smelting parameters in electric arc furnaces via carbon-thermal process by example of smelting FeSi using energy and technology criteria of ferroalloys furnace operation presented. It was shown, that while increasing values of energy and technology criteria, the specific consumption of electric power per one basic tonne of the alloy is reducing. For mid power electric furnaces that melted 75% FeSi, the energy and technology criteria of ferroalloys furnace operation corresponds to a range from 0.300 to 0.314. At the same time, the specific electric power consumption is from 9.0 to 8.6 MW∙h/t of the alloy. A satisfactory, but less efficient version of the furnace operation is the range of energy and technology criteria from 0.272 to 0.293 and specific electricity consumption of electric power varies from 9.8 to 9.2 MW∙h/t of alloy. Such a complex value can be considered as the main element of the energy and technological audit of the ferroalloy furnace facility, as well as to identify effective operating modes, analysis of usage of various types of charge materials (ore raw materials, carbonaceous reductants) and the application of innovative melting technologies.

Processing of copper electrolyte slimes with a carbonaceous reductant

Processing of copper electrolyte slimes with a carbonaceous reductant

Application of a Waste Carbon Material as the Carbonaceous Reductant During Silicon Production

It is important to study the application of alternative carbon reductants for industrial silicon smelting to reduce consumption of carbonaceous reducing agents, electricity, and CO2 emissions during silicon production. In this study, an industrial experiment was carried out in an 8 MVA submerged arc furnace using waste carbon material in place of approximately 20% partial reducing agents. The system was analyzed for silicon yield, power consumption, overall energy efficiency, CO2 emissions, and the utilization rate of carbonaceous materials. The system improved the efficiency of carbonaceous materials and decreased power consumption using alternative carbon reductants. The results have showed that use of waste carbon materials reduced carbon emissions per ton silicon by more than 19.14% and specific CO2 emissions decreased to 0.865 t.

The effect of the carbonaceous materials properties on the energy consumption of silicon production in the submerged arc furnace

Abstract The objective of this study was to use a statistical approach to determine the correlation of fixed carbon, volatile matters and moisture with the specific electrical consumption and exergy efficiency by collecting and analyzing an abundance of actual production data generated in silicon plants during the melting process of silicon produced in the submerged arc furnace (SAF). A high positive correlation (the r maximum value of 0.82) between the fixed carbon composition and the specific electrical consumption, as well as the perfect negative correlation (the r maximum value of −0.92) between the fixed carbon and the exergy efficiency were found, especially when the carbon materials contained a very high amount of graphitized carbon. Compared with the carbon materials without woodchips, the high correlation among the volatile matters, the specific electrical consumption and exergy efficiency was observed when using the carbon materials with woodchips. The influence of the proximate composition on the electrical consumption and exergy efficiency becomes stronger with the increase of the graphitized carbon content in the carbon materials. The analysis results can be used to support decisions when optimizing the proximate composition of the carbonaceous reductants in order to increase exergy efficiency and decrease electrical consumption costs, which is one of the biggest operating costs in the silicon furnace.

Analysis of Coal for Safe Producing Low Temperature Carbon Products

Solid products of low temperature carbonization in comparison with coke have the higher reaction and adsorption capacity, are easier to undergo the subsequent activation and gasification. The low temperature coke can also act as a refined smokeless fuel for boiler plants and domestic ovens, an active carbonaceous reductant for the chemical and metallurgical industries. The results of Tugnuisky open pit (Buryatia) coal quality studies are given in this article. The parameters of the technical and elemental analysis of the feed coal were tested during the experiments. The low temperature carbonization of coal sample in retort was carried out to determine the yield of the low temperature carbonization products. The produced products were investigated according to the quality indicators in accordance with the requirements of the technical specifications.

A Study of the Performance of Submerged Arc Furnace Smelting of Industrial Silicon

The consumption of energy and carbonaceous reductants is one of the more important factors that significantly influence the cost of industrial silicon production. The effect of raw materials on the silicon yield and the energy consumption in the process of producing silicon was investigated in this study using data collected from various submerged arc furnaces. Following analysis of a large quantity of industrial data, the results showed that a 12.5 MVA submerged arc furnace was the most efficient in utilizing the consumption of coal. In addition, the 8 MVA furnaces consumed the petroleum coke (petcoke) more efficiently in a silicon production process. To decrease the raw materials consumption and the energy loss in an industrial silicon production process, the petcoke/coal ratios for the 8 MVA and 12.5 MVA furnaces should be 1.25∼1.4 and 0.4∼0.6, respectively, for the production of one ton of silicon.

Effect of raw materials on the production process of the silicon furnace

The silicon industry is an energy-intensive industry with high energy operating costs and is currently facing new challenges to improve sustainability and become more competitive. Petroleum coke, coal, and charcoal are typically utilized as carbonaceous reductants for silicon production, and the mixture of different carbonaceous materials plays a very important role in the specific power consumption and the exergy efficiency of the process. Of these materials, in particular, charcoal preparation requires large amounts of wood, and continued and extensive deforestation contributes to ecological damage. Thus, it is urgent to study carbonaceous reductants that can be alternatives to charcoal or to find strategies that do not require the application of charcoal in the silicon production process. Exergy efficiency was used as an overall indicator to evaluate the effect of different carbon materials on the process of silicon production in this study. An exergetic efficiency of 0.39 was obtained for silicon produced with a mixture of woodchips and no charcoal. The overall exergy efficiency and the silicon yield exergy indicator results indicated that the addition of woodchips to a mixture of carbonaceous materials improved the performance of the silicon furnace, even if the fixed carbon contribution was lower. There was no change in exergetic efficiency (0.33) for the mixture of petroleum coke and coal as carbonaceous materials with or without charcoal and woodchips. Therefore, a mixture of petroleum coke and coal without charcoal can be used as carbonaceous reductants while maintaining the exergetic efficiency of the process of silicon production.

STUDY OF THE PHASE-AND-CHEMICAL COMPOSITION OF SILICON PRODUCTION FURNACE SLAGS

Metallurgical grade silicon produced in ore-smelting furnaces (OSF) generates a negligible amount of a furnace slag compromising the valuable smelted product quality. The purpose of the study was to analyze the factors of furnace slag formation with its further passing into silicon when released from the ore-smelting furnace, as well as to study the chemical composition of samples. The computer program was developed to forecast the yield of smelting products (crude silicon, dust-gas mixture, furnace slag) depending on the amount and chemical composition of loaded charge material, i.e. siliceous raw ore and carbonaceous reductants. The paper provides the results of studying OSF slag samples from the existing plant by metallographic, X-ray, and X-ray diffraction methods and electron probe microanalysis. The study showed the presence of entrapped silicon prills with intermetallic inclusions (Fe(Ti)Si, CaSi2), silicon carbide SiC, incompletely reduced α-SiO2-cristobalite and Al2O3, and formed complex oxides of impurity elements (CaO·SiO2). It was found that the amount of formed furnace slag and thus the chemical composition of smelted silicon depend on the optimal excess of solid carbon in charge (within 103–111 %) and stable electrical operation of the ore-smelting furnace.

DEVELOPMENT OF ORE-THERMAL MELTING TECHNOLOGY FOR AGGLOMERATED CHARGE CONTAINING TECHNOGENIC RAW MATERIAL IN SILICON PRODUCTION

Production of silicon in ore-thermal furnaces (OTF) by carbothermic reduction of quartzites is accompanied by large dust emission, containing significant amount of valuable silica (an average of 86 %). In this regard, works devoted to raw material base expansion due to return of technogenic wastes into technological process are of great significance. To be used in process of silicon smelting in OTF, the dust collected by gas treatment units, consisting of 120 microns particles with predominant fraction of +20 – 50 μm, has to pass through preliminary agglomeration (to prevent its possible fly from reaction zone with process gases). Since charge including agglomerated part must have sufficient strength during transportation and loading to OTF, liquid glass is suggested to be used as a binder with addition of aluminum-containing electrostatic precipitators containing resinous substances (polyaromatic hydrocarbons) as a hardening reagent for dust. Based on the results of tests for strength of the agglomerated charge samples, the following charge components ratio is recommended: 24 – 27 % of silicon production dust; 51 – 53 % of carbonaceous reductant (1:1 mixture of petroleum coke and charcoal); 4 – 5 % oversize of fine-grained silicon; 14 – 15 % of binder (liquid glass and dust of electrostatic precipitators of aluminum-magnesium production in 4:1 ratio) (by weight). With such a composition of charge, the drop resistance coefficient averaged 82.5 %. As a result of physical-chemical study of agglomerated compositions obtained by the proposed method, it was found that they have porous structure (45.5 %) which forms a well-developed active surface of material with an apparent density (1100 kg/cm3), which provides operation of OTF in a stable mode when using agglomerated charge of this composition. Experimental melting carried out in a HTF 17/10 type high-temperature furnace has resulted in a product containing more than 44 % (by weight) of silicon carbide as an obligatory intermediate in carbothermic process, that allows to recommend charge agglomerated by proposed procedure with selected component ratio for use as additives to the main (cobbed) charge in production of silicon by carbothermic method.