Carbothermal Reduction Process Research Articles

Effects of carbon on the synthesis and densification of tantalum carbide powder

Tantalum carbide (TaC) powder was synthesised at 1500 ºC by sol-gel and carbothermal reduction processes using tantalum pentachloride (TaCl5) and phenolic resin as the starting materials. The effects of the C/Ta ratios in the Ta-containing precursor on the reaction yield, microstructure, chemical composition, and sinterability of the powders were investigated. The results showed that a high C/Ta ratio was favourable for the formation of TaC powder. With an increase in the C/Ta ratio, the oxygen content of the powder decreased, whereas the free carbon content increased. Consolidated TaC ceramics with high relative density (> 97%) were obtained at 1900 ºC for 5min under 80MPa after sintering the powder synthesised at C/Ta ratios of 4.00 and above. However, the hardness and fracture toughness of the TaC ceramics were slightly reduced when the C/Ta ratio exceeded 4.00, owing to weak interface bonding caused by excessive free carbon in the powder. It was found that sintering TaC powders prepared at a C/Ta ratio of 4.00 produced dense TaC ceramics, with a Vickers hardness and fracture toughness of 16.54GPa and 3.72GPa∙m1/2, respectively.

Influence of localized thermal effect of microwave heating on the carbothermic reduction process of ZnFe2O4

As an environmentally efficient method, microwave heating has been proposed to recover Zn from electric arc furnace dust (EAFD) recently. During the process, microwave irradiation has been shown to promote the reaction by lowering the reaction temperature and activation energy, in addition to providing efficient heat. However, the mechanism by which microwave heating promotes the zinc removal reaction of EAFD remains unclear. Thus, this study focused on ZnFe2O4, the primary component of EAFD, and developed an electromagnetic-thermal-chemical reaction coupling model to investigate the factors influencing the carbothermic reduction process of ZnFe2O4 and analyze the promoting mechanism of the microwave on the reaction. The main results indicate that the localized thermal effect, determined by the microwave distribution, exacerbates temperature differences and leads to non-uniform reaction behavior inside the sample. Increasing microwave power and graphite addition enhances the localized thermal effect, worsening field uniformity. In the simulation, the localized thermal effect of microwave heating reduced the activation energy of the zinc removal reaction to 252.97 kJ/mol, with an R2 reaction model. The assistance of the non-thermal effect in enhancing ion diffusion leads to a significant decrease in the activation energy observed in the actual microwave heating experiments.

Controlled synthesis of tantalum-based solid solution and exploration of electrochemical properties as soluble anode for molten salt electrolysis

Metal oxycarbide solid solution possesses an extensive potential applications due to its remarkable physical features. In this paper, TaCxO1-x solid solution is successively and controllably synthesized by carbothermal reduction of Ta2O5. Based on the thermodynamic calculation, the possible reactions under different conditions in the carbothermal reduction process were analyzed, which provides theoretical guidance for controllable regulation and optimization of carbon thermal reduction process. The effects of carbon content, sintering temperature, and holding time on the synthesis of TaCxO1-x solid solution were investigated and the ideal process parameters for the synthesis of single-phase solid solution were identified. A single-phase solid solution with a carbon‑oxygen ratio close to 1:1 can be created as a soluble anode if the synthesis temperature is 1500 °C, the holding period is 6 h, and the molar ratio of C/Ta is 3.42. Moreover, the process feasibility of preparing metal tantalum by electrolysis of tantalum-based soluble anode is discussed, which provides a new method for metal tantalum preparation.

Effect of calcium aluminates content on the formation of Сa-α-SiAlON ceramics obtained by hot-pressing

This study explores a novel method for fabricating Ca-α-sialon ceramics using a calcium aluminate oxide eutectic additive. Conventional sintering techniques for Ca-α-sialon ceramics employ nitrogen-containing additives to facilitate the Si–N bond substitution mechanism with Al–O and Al–N bonds. In this work, calcium aluminate additives are utilized, leading to the formation of Ca-α-sialon ceramics via carbothermal reduction processes and partial nitridation of aluminum oxide. The influence of varying calcium aluminate content (5, 10, 15, 30, and 40 wt%) on the phase composition of Ca-α-sialon ceramics, produced by hot pressing at 1650 °C in a nitrogen atmosphere, was investigated. Results indicate that increasing the calcium aluminate content leads to the formation of a β-sialon phase, which subsequently transforms into Ca-α-sialon. At 40 wt% calcium aluminate, complete conversion of α-Si3N4 to Ca-α-sialon is achieved, with significant glassy phase formation at the grain boundaries. The study elucidates the relationship between calcium aluminate content, phase composition, lattice parameters, mechanical properties, oxidation resistance, and thermal expansion of the ceramics.

Recovery of lithium from spent NMC batteries through water leaching, carbothermic reduction, and evaporative crystallization process

The demand for lithium grows exponentially due to its expanding range of applications. Because of their composition, spent lithium-ion batteries represent a promising secondary source of lithium. The present work focuses on a two-stage lithium recovery process applied to two different black masses from NMC 622 electric vehicle batteries after prior crushing and separation stages. In the first stage, hydrolysis is used to extract lithium compounds from the degradation products of the electrolyte (LiPF6). In the second stage, a carbothermic reduction process is carried out in which various reducing agents are evaluated. The result of this stage is a product that is leached with water and crystallised by evaporation. The result of the first stage is two industrially useful compounds: LiF, which is used in the production of lithium-ion battery electrolytes, and Li3PO4, which is used in the production of lithium-iron-phosphate batteries. In the second stage, Li2CO3 is recovered with a remarkably low LiF content, with a purity higher than 98.4 %. This process allows 90–94 % of the total lithium in the black mass to be recovered.

Antimony nanoparticles encapsulated in interconnected nitrogen-doped carbon nanospheres for high performances PIBs

Antimony (Sb) has attracted significant attention as an anode material for potassium-ion batteries (PIBs) due to its high theoretical capacity and suitable working voltage. However, the severe volume variations of Sb during potassiation/depotassiation process lead to sluggish kinetics and poor cyclic stability for PIBs. In this study, Sb nanoparticles are confined within interconnected N-doped carbon nanospheres (Sb@NC) through an effective carbothermal reduction process. The potassium storage performances and mechanism are elucidated through electrochemical tests combined with ex-XRD analysis. When used as an anode for PIBs, the optimized Sb@NC-2 anode exhibits excellent cycle stability of 463.0 mAh g−1 at 200 mA g−1 over 100 cycles and superior rate capability of 113.4 mAh g−1 at a high current density of 2 A g−1. Besides, a full cell comprising an Sb@NC-2 anode and a PTCDA cathode is also tested to validate the practical feasibility of the anode. Furthermore, Density Functional Theory (DFT) calculations demonstrate that N-doped carbon can enhance the adsorption of K+ and improve the kinetics of electrochemical reactions. Therefore, the unique yolk-shell structure in this study effectively restricts volume expansion and aggregation of Sb particles while facilitating rapid electron/ion transfer. These findings provide a potential alternative anode material for advanced PIBs.

Bio-Carbon Assisted Carbothermal Reduction Process for the Recovery of Lithium and Cobalt from the Spent Lithium-Ion Batteries

Bio-Carbon Assisted Carbothermal Reduction Process for the Recovery of Lithium and Cobalt from the Spent Lithium-Ion Batteries

Construction of multi-interface magnetic FeMnC modified carbon/graphene aerogels for broadband microwave absorption

Magnetic carbon-based aerogels with low-density and strong attenuation, have attracted significant attention as microwave absorbing materials, but still face huge challenges. Herein, magnetic FeMnC modified carbon/Graphene aerogels (NCMF) were synthesized utilizing freeze casting following a carbothermal reduction process. The conductivity, defects density, material component and electromagnetic properties can be regulated by the temperature. The NCMF aerogels exhibit remarkable microwave absorption properties, with an effective absorption bandwidth of 5.76 GHz at a thickness of 2.1 mm and a minimum reflection loss as low as −50.8 dB at 7.52 GHz with a fill ratio of only 5 wt%. The exceptional microwave absorption capabilities of NCMF aerogels are attributed to the synergistic effects of dielectric loss, magnetic loss, three-dimensional (3D) carbon conductive network, and the optimal impedance matching. Consequently, this research paves a way for the development of microwave absorbing materials with lightweight, broadband and strong microwave absorption at low loading.

In situ steam oxidation of nickel phosphide/carbon composite nanofibers as anode materials for lithium-ion batteries

The synthesis of self-standing nickel phosphide/carbon (NixP/C) composite nanofibers is accomplished through a one-pot electrospinning and in situ steam oxidation after the carbothermal reduction process. Control over the levels of in situ steam oxidizers in the forms of crystal water and nitrates in the precursor fibers is achieved by systematically adjusting the drying temperature before the high-temperature heat treatment. This led to structural modifications in the final products analyzed through comprehensive characterizations. Mechanistic insights into the in situ steam oxidation process are provided, emphasizing its potential in optimizing electrode materials. Electrochemical assessments reveal significantly improved performance in the sample prepared from the media with optimal content of oxidizers, attributed to a tailored surface oxide layer, electronic configuration, and microstructure, enabling enhanced reaction kinetics and minimizing volume expansion. This results in exceptional cycling stability and notable capacity retention during prolonged charge-discharge cycles. Thus, NixP/C achieves the highest initial charge capacity of 719.5 mAh g−1 with an initial Coulombic efficiency of 61% and maintains a high capacity of 590.7 mAh g−1 after 100 cycles at a current density of 0.1 A g−1.

Optimization of sintering process to fabricate high-density ultrafine-grained (HfNbTaTiZrW)C ceramic: A comparative study

The fabrication of senary carbide (HfNbTaTiZrW)C was achieved by carbothermal reduction process combined with three different kinds of sintering paths, including conventional single-step sintering (CS) and two kinds of two-step sintering (TSS-1 and TSS-2). It is revealed that the synthesized nanosized powders (∼102 nm) through carbothermal reduction exhibited excellent sintering capability to obtain a high density single-phase solid solution with homogeneous metal cation distributions at macro- and sub-micrometer scales, while atomic-level heterogeneity existed with Zr segregation. Compared to CS samples with bimodal microstructure, the application of two-step sintering significantly reduced the amounts of intergranular pores and (ZrHf)O2, accompanied with grain refinement. In particular, a well-designed TSS-2 route comprising short-term high-temperature followed by low-temperature sintering achieved ultrafine-grained bulk with grain size of 1.44±0.22 μm and excellent mechanical properties of elastic modulus of 480 MPa, microhardness of 23.4 GPa, and fracture toughness of 3.8 MPa·m1/2.

Utilizing pulverized waste polyvinyl chloride film as an alternative reducing agent for iron ore reduction

The research into using waste plastics as a substitute for coal powder and coke as a reducing agent has garnered significant attention, driven by various factors such as increased environmental concerns and growing interest in sustainable materials. This study investigates the process of carbothermal reduction using a mixture of waste polyvinyl chloride (PVC) and iron concentrate. Thermogravimetric analysis demonstrated that the heat-treated polyvinyl chloride products (PVC370) exhibited superior reaction properties compared to anthracite. Reduction tests indicated that PVC370-bearing pellets were less sensitive to temperature changes than anthracite-bearing pellets, highlighting a potential advantage of PVC370 in industrial applications. Moreover, the metallization ratio of PVC370-bearing pellets exceeded that of anthracite-bearing pellets before reaching 1150 °C. At a temperature of 1100 °C and a C/O of 0.8, the metallization ratio of PVC370-bearing pellets peaked at 83.17 %. During the reduction process of PVC370-bearing pellets, hydrogen (H2), carbon monoxide (CO), and hydrogen chloride (HCl) were efficiently released at relatively low temperatures. The efficiency of gas release in the reduction process could be attributed to certain factors, such as the composition or structure of the PVC370-bearing pellets. Notably, the quality of gasses generated during the reduction process of PVC370-bearing pellets is superior to that of anthracite-bearing pellets, even when considering chlorine content.

Briquette Shape Roles in Carbothermal Reduction Process of Limonitic Laterite Nickel

Lateritic ore carbothermalreduction is currently the focus of many researchers. This process uses a relatively lower temperature of operation than the smelting. Therefore, the carbothermal reduction process has a relatively lower primary energy demand and CO2 gas emissions. This research examines the appropriate briquette form to obtain the optimum recovery, concentration of nickel, and selective reduction of nickel, as well as analyzes the compounds/phases formed. The briquette in this study was formed into three different geometries, i.e., the pillow, spherical, and cylindrical forms. First, this research was carried out by mixing the raw materials and forming it into specified briquette forms. Second, the formed briquettes were put into a crucible. Third, the coal-limestone bed mixture was used to cover the briquettes. Then, the carbothermic reduction process was started by heating to 700 oC for 2 hours and continued to 1400 oC for 6 hours. Finally, the magnetic separation process was performed to separate the reduced briquettes. As a result, the cylindrical shape briquette obtained better results at 6.74% Ni, with a nickel recovery of 96.20% and a selectivity factor value of 10.39. The compounds formed after carbothermic reduction process products include FeNi, Fe3Si, and SiO2. In a spherical-shaped briquette, Fe3O4 and Mg2SiO4were found in the reduced product, indicating impurities in the reduced briquettes.

Planetary Soil Simulant Characterisation: NU-LHT-2M Study Case to Support Oxygen Extraction Lab Tests with a Low-Temperature Carbothermal Process

Since the landing on the lunar surface, the lunar regolith has begun to interact in different ways with landed elements, such as the wheels of a rover, astronaut suits, drills, and plants for extracting oxygen or manufacturing objects. Therefore, a strong effort has been required on Earth to fully characterise these kinds of interactions and regolith utilisation methods. This operation can only be performed by using regolith simulants, soils that are reproduced with the Earth’s rocks and minerals to match the real features. This article presents the main guidelines and tests for obtaining the properties of a generic simulant in terms of composition, physical and mechanical properties, solid–fluid interaction, and thermal properties. These parameters are needed for the designing and testing of payloads under development for planned lunar surface missions. The same tests can be performed on lunar, martian, or asteroid simulants/soils, both in laboratory and in situ. A case study is presented on the lunar simulant NU-LHT-2M, representative of the lunar highlands. The tests are performed in the context of an in situ resource utilisation (ISRU) process that aims to extract oxygen from the lunar regolith using a low-temperature carbothermal reduction process, highlighting the main regolith-related criticalities for an in situ demonstrator plant.

Kinetics of microwave carbothermal reduction of Sb2O3: Isothermal and non‐isothermal microwave thermogravimetric analysis

AbstractKinetics of antimony production via carbothermal reduction of Sb2O3–carbon powder–NaCl mixture using microwave and conventional heating was investigated to identify the dominant controlling mechanism. Results of conventional heating revealed the temperature range of conventional carbothermal reduction reaction is 500°C to 800°C, with the average activation energy of each stage being 81.97 kJ/mol (α = 0.1–0.5), 65.17 kJ/mol (α = 0.5–0.75), and 69.86 kJ/mol (α = 0.75–1.0), respectively. In the microwave field, the carbothermal reduction reaction of raw materials can be completed at 600°C to obtain antimony, and the weight loss data of the carbothermal reduction process were recorded for the first time. The above results show that the microwave field enhanced the interfacial chemical effect, accelerated the interfacial diffusion from the metal phase to the oxide phase, and reduced the activation energy of the carbon thermal reduction process to 6.85 kJ/mol. The growth index of antimony grain growth process is estimated to be 4.33, controlled by the surface diffusion. These data provide a reliable theoretical basis for studying the reduction reactions of minerals in microwave fields.

Coproduction of silicon nitride & oxynitride whiskers and precipitated silica from industrial rice husk ash

Rice industrialization generates large amounts of rice husk, and when this husk is burned, substantial volumes of ash are produced as a result. The lack of a sustainable application for these ashes constitutes a serious environmental liability. Employing rice husk ash as a starting material to manufacture higher-value products fulfills both environmental and economical purposes. Particularly, the presence of silica and carbon in intimate contact makes rice husk ash an attractive precursor for carbothermal reduction and nitridation processes. In the present work, a pre-treatment was applied to a locally sourced industrial rice husk ash, aiming to render not only a more appropriate starting material for carbothermal reduction and nitridation, but also precipitated silica as a by-product. This process involved a simple alkaline digestion step followed by filtering and acid precipitation of the solubilized silica. For carbothermal reduction and nitridation, the treated ash was introduced in graphite crucibles with graphite lids and held at soaking temperatures between 1200 °C and 1400 °C under a nitrogen atmosphere for 3 h. The pretreatment imposed on the ash permitted the adjustment of the carbon-to-silica ratio, producing a substantial improvement in the carbothermal reduction and nitridation results, and enabling the simultaneous obtention of precipitated silica. α- and β- silicon nitride, and silicon oxynitride whiskers were obtained through carbothermal reduction and nitridation of the treated rice husk ash. The whiskers obtained had lengths in the millimeter range with cross-sections ranging from about 100 nm up to 500 nm.

Mechano-thermic reduction of low-grade titanium ore for high-grade TiO2 synthesis

A systematic study on the mechano-thermic reduction of low-grade ilmenite concentrate for the production of high-grade TiO2 powder used in the production of non-oxide ceramics for cutting tool applications has been successfully carried out. Samples were prepared via planetary ball milling and carbothermic reduction processes, and the as-reduced product was subsequently leached in order to improve the synthesized TiO2 by removing the metallic iron in it and other minor soluble impurities dissolved in the iron. The mechano-thermic reduction was achieved by milling a representative mixture of ilmenite and carbon in a molar ratio of 1:1, followed by carbothermic reduction at 1000 °C in a laboratory high-temperature furnace for 60 min. The as-reduced product was subsequently leached at 80 °C for 6 h in a hydrochloric acid solution. It was found that there was a complete reduction of ilmenite to metallic iron and TiO2 at 1000 °C. The results of the FESEM showed there were only two distinct regions of metallic iron (bright region) and titanium dioxide (grey region) with minor traces of unreacted carbon (dark spots), although there was clear regional demarcation between these regions. However, the iron dissolution during the acid treatment was almost 100% as there were no peaks of iron in the as-leached powder. The results of these analyses confirmed the synthesis of high-grade TiO2, which finds application in cutting tool applications and other areas such as in reflective pigment production.

Research of Bayan Obo tailings characteristics and recovery methods

This paper presents a new method for the recovery of iron and rare earth elements (REEs) from Bayan Obo tailings, which are the waste materials from the extraction of iron and REEs from the Bayan Obo ore deposit in Inner Mongolia, China. The method is based on the combination of microwave-assisted carbothermal reduction and acid leaching. The microwave-assisted carbothermal reduction can effectively reduce the iron oxides and REE oxides in the tailings to metallic iron and REE metals, respectively, and separate them from the gangue minerals. The acid leaching can then dissolve the REE metals from the reduced product and obtain a high-purity REE solution. The effects of various parameters on the performance of the method were investigated and optimized, and the mechanisms and kinetics of the reactions were analyzed and modeled. The results showed that the method can achieve a high recovery rate of iron and REEs, a high selectivity of REEs, a low energy consumption, and a simple process. The economic and environmental benefits of the method are also significant, as it can utilize the Bayan Obo tailings and recover the valuable elements from them, and reduce the waste generation and greenhouse gas emission. The method provides a new and efficient technology for the utilization of Bayan Obo tailings and the recovery of iron and REEs, and contributes to the fundamental understanding of the microwave-assisted carbothermal reduction and acid leaching processes.

Non-isothermal kinetics and thermodynamics analysis of vanadium-titanium magnetite

Thermodynamic calculations and thermal analysis tests were performed to investigate the thermodynamic and kinetic behaviors of the carbothermal reduction of vanadium-titanium magnetite w(C)/w(O) and basicity on the carbothermal reduction process of vanadium-titanium magnetite based on the HIsmelt process. Thermodynamic analysis showed that the addition of basicity promoted the reduction of vanadium-titanium magnetite, and the reaction onset temperature gradually increased with the decrease of the valence states of the elements V, Ti and Fe in the product. Increasing the amount of carbon assigned to the system gradually increased the mass fractions of metal Fe and Fe3C and raised the mass fractions of Ti, V and their low valence compounds at equilibrium. Increasing the basicity had less effect on the Fe, V and Ti fractions of the equilibrium system. The results of kinetic tests showed that the maximum reduction degree and maximum reaction rate of the reduction reaction by increasing w(C)/w(O) and basicity increased, the apparent activation energy and the finger front factor decreased, and the reaction mechanism function of the non-isothermal kinetic reduction process was f(α) = (3/2)(1−α)4/3[(1−α)−1/3−1] −1 belonging to the three-dimensional Z-L-T diffusion model.

Cleaner extraction of white phosphorus from phosphate rock through molten salt electrolysis

White phosphorus (P4) is an essential raw material for the production of phosphorus chemicals. The conventional carbothermal reduction process used to extract P4 from phosphate rock is known as energy intensive and environmentally polluting, posing obstacles to meeting the urgent global demands for clean production and carbon neutrality. Moreover, the low product purity restricts its application in high-value industries. This paper presents an original approach that is both simple and coke-free for extracting high-purity P4. The method involves electrolyzing dissolved phosphate rock in molten CaCl2 at a mild temperature. We undertake an in-depth investigation into the dissolution behavior of phosphate rock in molten CaCl2 and the electrolysis behavior of the melt. The experiments demonstrate the rapid dissolution of phosphate in the rock when exposed to molten CaCl2, reaching saturation within a short time (e.g., within 10 min at 850 °C). The dissolution of phosphate shows a preference over silicates present in the phosphate rock. The electrochemical reduction of PO43− in molten CaCl2 is electrochemically reversible, as observed at potential scan rates not exceeding 0.20 V s−1. The obtained P4 product through electrolysis is of higher purity compared to the industrial-grade commercial product produced via carbothermal reduction. The implementation of pre-electrolysis can further improve the purity of the product and the current efficiency of the electrolysis process. The theoretical electricity and carbon consumption in the electrolysis method are estimated to be 9.12 kWh and 0.53 kg, respectively, for every 1 kg of P4 produced. These values are lower than the conventional carbothermal reduction process. This cutting-edge electrolysis method represents a paradigm shift towards a more sustainable development of the phosphorus chemical industry, thereby showcasing its potential for revolutionizing the field.

Phase Reduction and Thermodynamic Analysis of Ilmenite Ore by Carbothermal-Iodination using Different Carbon Reductants

The present study is on the combination of carbothermal reduction and iodination reaction (carboiodination) process for the phase reduction of ilmenite ore (FeTiO3). The aim is to understand the phase reduction and thermodynamic reaction analysis of ilmenite ore by a combined method of carbothermal-iodination using different carbon reductants (graphite and palm char). Graphite was used as a standard carbon reductant while palm char as a renewable carbon reductant was prepared via the pyrolysis technique. Ilmenite was mixed with carbon reductants and then first reduced by using a carbothermal reduction process at 1550℃. Then, the reduced samples were further investigated with iodination reaction in different temperature ranges of 900-1000 °C using a vertical tube furnace with mixed argon and iodine gas (0.2 L/min). The proximate and ultimate analyses of carbon reductants were analysed by CHON analyser and their microstructure by using SEM, while XRF and XRD were used for analyzing the chemical compositions and the phase reductions of raw ilmenite ore and reduced samples, respectively. The thermodynamics of possible reactions during carbothermal-iodination reactions were calculated by HSC Chemistry 6.0 software. By comparing graphite and palm char, palm char had an amorphous structure, with porous and high carbon content showing high potential for usage as a reductant in titanium extraction from ilmenite ore. The phases of ilmenite ore were ilmenite, rutile, and anatase transformed into rutile, pseudobrookite, and titanium oxide detected by XRD. Further reduction was performed by palm char where more rutile (TiO2) and titanium oxide (Ti3O5) developed from the iodination reaction at the highest temperature compared to graphite due to better properties and amorphous structure. The rutile and titanium oxide were found as stable phases from the thermodynamic analysis and confirmed with XRD. From the findings, the combination of carbothermal-iodination of ilmenite ore was possible and promising for rutile (TiO2) production in mineral extractions.