Carbon Thermal Reduction Research Articles

Experimental Study on the Recovery of Arsenic and Iron from Arsenic–Iron Precipitate by Carbon Thermal Magnetization Reduction

Arsenic–iron precipitate was treated using a carbon thermal magnetization reduction method in order to recover arsenic and iron. Arsenic–iron precipitate mixed with coke powder was roasted at a low temperature; arsenic was recovered in the form of As2O3, and iron was recovered in the form of Fe3O4. The volatilization rate of arsenic was 97.45%, and the content of arsenic in the precipitate was decreased to 0.60%. Iron and arsenic were recovered in the form of Fe3O4 and As2O3 with a purity of 99.91 wt.% under the conditions of a roasting temperature of 650 °C, coke powder addition of 25 wt.%, a roasting time of 180 min, and an argon flow rate of 10 L/min. The volatilization of arsenic was controlled by a chemical controlling step at 20–100 min, and this was switched to a diffusion controlling step at 120–180 min by kinetic experiments. The reaction mechanism of arsenic and iron under carbon thermal magnetization reduction was as follows: in the early stage of the reaction, a large amount of FeAsO4 was decomposed into As2O3 and Fe3O4; in the middle and late stages of the reaction, FeAsO4 was continuously decomposed and reduced, and the content of Fe3O4 was continuously increased until all iron was magnetized to generate Fe3O4, and the decomposed As2O3 volatilized into dust. Arsenic reacted with CaO to generate Ca3(AsO4)2, and this may be the reason why arsenic could not be removed completely.

Guest Ion-Dependent Reaction Mechanisms of New Pseudocapacitive Mg3 V4 (PO4 )6 /Carbon Composite as Negative Electrode for Monovalent-Ion Batteries.

Polyanion-type phosphate materials, such as M3 V2 (PO4 )3 (M = Li/Na/K), are promising as insertion-type negative electrodes for monovalent-ion batteries including Li/Na/K-ion batteries (lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), and potassium-ion batteries (PIBs)) with fast charging/discharging and distinct redox peaks. However, it remains a great challenge to understand the reaction mechanism of materials upon monovalent-ion insertion. Here, triclinic Mg3 V4 (PO4 )6 /carbon composite (MgVP/C) with high thermal stability is synthesized via ball-milling and carbon-thermal reduction method and applied as a pseudocapacitive negative electrode in LIBs, SIBs, and PIBs. In operando and ex situ studies demonstrate the guest ion-dependent reaction mechanisms of MgVP/C upon monovalent-ion storage due to different sizes. MgVP/C undergoes an indirect conversion reaction to form Mg0 , V0 , and Li3 PO4 in LIBs, while in SIBs/PIBs the material only experiences a solid solution with the reduction of V3+ to V2+ . Moreover, in LIBs, MgVP/C delivers initial lithiation/delithiation capacities of 961/607 mAh g-1 (30/19 Li+ ions) for the first cycle, despite its low initial Coulombic efficiency, fast capacity decay for the first 200 cycles, and limited reversible insertion/deinsertion of 2 Na+ /K+ ions in SIBs/PIBs. This work reveals a new pseudocapacitive material and provides an advanced understanding of polyanion phosphate negative material for monovalent-ion batteries with guest ion-dependent energy storage mechanisms.

Identifying features in the structural and phase composition of the products of recycling of the scale of high-speed cutting steel by carbon thermal reduction

This paper reports a study into the features of the structural-phase composition of products from the carbon-thermal reduction of scale of high-speed steels that yields an alloying additive. This is necessary to determine the technological parameters that reduce the loss of target elements in the process of obtaining and using resource-saving alloying material. The study indicates that when the degree of scale reduction changed from 28 % to 67 % and 81 %, an increase in the manifestation of a solid solution of carbon and alloying elements in the α-Fe lattice was observed. At the same time, the intensity of the diffraction maxima of FeO and Fe3O4 decreased. In the reduced products, the presence of Fe3C, FeW3C, Fe3W3C, and WC was traced. With an increase in the degree of scale reduction from 28 % to 67 %, the disordered (of "loose" appearance) microstructure was replaced with the formed particles of round and multifaceted shape with different content of alloying elements. At the reduction stage of 81 %, the microstructure had a finely fibrous structure. Based on the suite of studies, the most acceptable degree of reduction of scale of high-speed steel, followed by the use of the obtained material as an alloying additive, is 81 %. At the same time, ensuring the degree of recovery at the level of 67 % would also suffice. This is due to the fact that residual carbon in the form of carbides provides an increased reducing ability and degree of assimilation of alloying elements with the restoration of the residual oxide component in the liquid metal during doping. Spongy microstructure contributes to faster dissolution, in relation to the corresponding standard ferroalloys. This ensures a reduction in the total smelting time and, as a result, a decrease in the energy consumed

Hollow multi-shell SiC@C@PANI nanoparticles with broadband microwave absorption performance

The hollow multi-shell structure has been used as a basic concept for the design and preparation of microwave absorbing (MA) materials. Herein, we prepared novel hollow SiC@C@PANI (SCP) nanoparticles by a two-step in situ polymerization method, template method and carbon thermal reduction method. By coating different proportions of polyaniline (PANI) on the surface of SiC@C microspheres to regulate the impedance matching and reduce the escape of electromagnetic waves, the suitable dielectric loss and impedance matching reach an optimal balance, the multilayer heterogeneous interface significantly improves the polarization relaxation behavior, and the hollow structure enhances the multiple reflections and scattering of electromagnetic waves. Finally, the effective absorption bandwidth (EAB) of SCP-1:1.5 reached 5.61 GHz at only 1.88 mm. Moreover, we designed and optimized the macroscopic structure of the MA metamaterial through gradient modulation, and successfully broadened the EAB to 10 GHz by introducing multiple interferences, which completely covers the X, Ku bands. Simultaneous optimization strategies for microscopic design and macroscopic regulation of hollow multi-shell absorbers provide ideas for breaking the performance boundaries of MA materials.

Unique Spindle-Like Bismuth-Based Composite toward Ultrafast Potassium Storage.

Bismuth (Bi)-based materials have attracted great attention as anodes in potassium ion batteries (PIBs) for their high theoretical capacity and suitable voltage range. Herein, the authors report a unique spindle-like structured Bi@N-doped carbon composite (SPB@NC) consisting of interconnected nano-Bi coated heteroatom-doped hard carbon layer via an interesting insitu carbon thermal reduction method. The special interconnected Bi nanoparticles gradually form porous structure with ample inner voids for accommodating volume variations while the N-doped carbon layer not only keeps the electrode stable, but also contributes to rapid electron/ion transfer. As a result, such a robust framework endows SPB@NC fast potassium storage with outstanding capacity of 276.5mAhg-1 at 30Ag-1 (i.e., 1min for discharge/charge) and durable cycling performance of 299.3mAhg-1 at 5Ag-1 after 2000cycles. Notably, a full cell assembled with potassium vanadate cathode is promising for practical applications. A series of exsitu techniques reveals the in-depth potassium storage mechanism and kinetics reactions. This work illuminates helpful insights into Bi-based anodes for PIBs.

A stable anode-free Na-S full cell at room temperature

The extended cycling life of room-temperature Na-S batteries depends predominantly on the excessive Na metal. Inhibiting Na corrosion by soluble Na polysulfides (NaPS) and reducing the usage of Na metal are key challenges to achieve practical Na-S batteries. Herein, an anode-free Na-S full cell is assembled with Na2S@carbon paper cathode prepared by in situ carbon-thermal reduction of Na2SO4, and 3D current collector (3DCC) of carbon nanofibers at the anode side, extraordinarily using Fluoroethylene carbonate (FEC) as electrolyte additive. This Na2S-based 3DCC||Na2S full cell not only provides stoichiometric Na source but also permits FEC to participate in formation of SEI on 3DCC ahead of the production of soluble NaPS during the initial charging, overcoming the incompatibility of FEC in Na-S battery. The polysulfide-resistant SEI guarantees the stable plating/stripping of volume-expansion alleviated Na metal on 3DCC. The as-developed anode-free 3DCC||Na2S full cell demonstrates 500-cycle life at 0.5 C, delivering much higher overall energy density than those using excessive Na metal. This is the first report of rechargeable anode-free Na-S battery with satisfactory cycling durability, representing a significant step toward achieving practical Na-S batteries.

One-step preparation of Fe/N co-doped porous biochar for chromium(VI) and bisphenol a decontamination in water: Insights to co-activation and adsorption mechanisms

Herein, magnetic nitrogen doped porous biochar (Fe/N-PBC) was prepared by mixing KHCO3, K2FeO4 and CO(NH2)2 through one-step pyrolysis, and was employed for adsorbing Cr(VI) and BPA in water. The whole co-activated process was accompanied with pore-forming, carbon thermal reduction and element doping. Specifically, the developed microporous structures and high surface area of Fe/N-PBC (1093.68 m2/g) were achieved under synergistic activation of KHCO3 and K2FeO4. Meanwhile, carbon thermal reduction process successfully converted K2FeO4 to Fe0 with introduction of heterocyclic-N (pyrrolic N and pyridinic N) structures by CO(NH2)2 doping. Fe/N-PBC exhibited outstanding uptake for Cr(VI) (340.96 mg/g) and BPA (355.14 mg/g), and possessed favorable regeneration properties after three cycles. Notably, the high-performance Cr(VI) removal was associated to reduction, electrostatic interaction, complexation, pore filling and ion exchange, while pore filling, hydrogen-bonding interaction and π-π stacking were responsible for BPA binding. This work presents reasonable design of Fe/N-carbon materials for Cr(VI)/BPA polluted water remediation.

Carbon thermal reduction of waste ternary cathode materials and wet magnetic separation based on Ni/MnO nanocomposite particles

The widespread use of lithium-ion batteries and the increase in the number of new energy electric vehicles have brought more waste batteries to be recycled. In this paper, a new combined process for in-situ recycling of wasted ternary lithium batteries using graphite for carbon thermal reduction with the cathode material under nitrogen atmosphere, after which the nanocomposite particles formed by the reduction products were separated and recovered by wet magnetic separation, has been proposed. The carbon thermal reduction products were Li2CO3, Ni, Co and MnO, respectively, and Ni and Co could form nanocomposite particles with MnO in the thermal reduction process. The reaction mechanism of the carbon thermal reduction reaction of anode materials and the effects of carbon thermal reduction temperature, wet magnetic separation time and solid-to-liquid ratio on the recovery rate were investigated. The recovery rate of Li, Ni, Co and Mn were 95.57 %, 96.44 %, 94.88 % and 94.98 %, respectively, under the optimum condition of reaction temperature of 650 °C, wet magnetic separation time of 75 min and solid-liquid ratio of 15 g/L, respectively.

Preparation and electromagnetic wave absorption properties of SiC/SiO2 nanocomposites with different special structures

The special microscopic morphology and structure of electromagnetic (EM) wave absorbing materials are the key factors affecting their performance of EM wave absorption. In this work, three different special structures of SiO2/SiC nanocomposites (hollow spherical SiO2/SiC composite nanoparticles (HSPs), core–shell SiO2/SiC composite nanofibers (CSFs) and core–shell SiO2/SiC composite nanochains (CSCs)) are successfully prepared by self-assembly technology and high-temperature carbon thermal reduction method in a single crucible. The EM wave absorbing properties of them are investigated. The results show that HSPs have superior EM wave absorbing performance compared to CSCs and CSFs. The HSPs with a low filler loading of 10 wt% exhibit minimum reflection loss (RLmin) of −52.73 dB at 14.50 GHz with a thickness of 2.64 mm. Moreover, the maximum effective absorption bandwidth (EABmax) is up to 7.79 GHz (10.21–18 GHz) under a corresponding thickness of 2.62 mm. The special hollow spherical structure not only provides a large number of interfaces to enhance interfacial polarization, but also improves impedance matching characteristics, resulting in excellent EM wave absorption performance of HSPs. Thus, this work provides a reference for the structural design of an ideal EM wave absorber.

Electrochemical Properties of Layered LiMoO<sub>2 </sub>as Cathode for Li-Ion Batteries

With the development of new energy vehicles, it is necessary to develope new fast charging cathode materials for lithium ion batteries. This paper reports a simple carbon thermal reduction routine to synthesize layered LiMoO2 cathode for Li-ion batteries. Impurity-free micro-crystalline powders were synthesized by one-step method with a thermal treatment at 800°C for 5 hrs under N2 atmosphere. The structural, morphological and electrochemical properties of LiMoO2 were characterized by using X-ray diffraction pattern (XRD), scanning electronic microscopy (SEM), charge/discharge cycling and electrochemical impedance spectroscopy (EIS). The diffraction results indicate that the prepared sample has a layered hexagonal structure related to α-NaFeO2. The secondary particles are in order of 2.0 μm length on average with homogeneous distribution. The initial discharge capacity of LiMoO2 is 110.9 mAh·g-1 at 0.1 C, and the capacity can still remain 92.8 mAh·g-1 after 100 cycles. The good cycling performance and high rate discharge performance are attributed to the smaller charge-transfer resistance revealed by EIS results.

Optimization of response surface methodology (RSM) for defluorination of spent carbon cathode (SCC) in fire-roasting aluminum electrolysis

• Response surface methodology can effectively remove fluoride from SCC. • Determine the optimal treatment process in a conventional muffle furnace. • When the roasting temperature is 1499 °C, the treatment time is 3.33 h, and the average particle size is 10 mm, the fluorine removal rate reaches 88%. Spent carbon cathode (SCC) is a typical toxic and hazardous solid waste generated in aluminum electrolysis. The harmless treatment of SCC is extremely important for the aluminum electrolysis industry. Herein, the response surface methodology was used to investigate the best process for removing fluoride from the SCC of aluminum electrolysis using the roasting method. A Box–Behnken design (BBD) was used to investigate the effects of three independent variables, namely, particle size, roasting temperature, and treatment time, on the fluorine removal rate of the SCC. Seventeen groups of experiments were conducted according to these three factors. Statistical analysis system software and a second-order polynomial model were used to analyze the data and predict the response. The results showed that the particle size, roasting temperature, and treatment time significantly influenced fluoride removal in the SCC. Under optimum process conditions, the system predicted a fluoride removal rate of 87% for the SCC. Validation experiments were conducted on the fluoride removal rate of the SCC under optimum process conditions. The results showed that the actual value reached 88%. The X-ray diffraction analysis before and after calcination showed that a small amount of SiO 2 was converted into SiC through a carbon thermal reduction reaction after calcination. This paper provides a theoretical basis for the best process of roasting SCC to remove fluoride. It also has a certain guiding significance for other solid waste treatments.

Investigation of the parameters influence of a cylindrical inductor with two-layer inwall on its temperaturePhysico-chemical prerequisites for decarburization of carbon-thermal reduction products Cr2O3

The development of physicochemical bases for solid-phase reduction of ore and man-made materials makes it possible to obtain spongy ligatures with specified properties. The use of such materials in metallurgy can significantly save mineral and energy resources. The thermodynamic analysis of the process of carbon-thermal reduction of chromium-containing raw materials to determine the conditions for obtaining an alloy with low carbon content. A six-factor mathematical planning experiment was performed using a half-replica of a complete factorial experiment. The analysis of solid-phase reduction of chromium-containing charge was carried out taking into account the following factors: temperature, time, gas phase composition, C/O, Cr/Fe and Fe/Ni ratios. A regression equation is obtained, which makes it possible to quantify the optimal value of each factor. By phase analysis of the Cr-O-C and Cr-Fe-O-C systems, the conditions that ensure the reduction of carbon in the final product are determined. The conditions for the appearance of metastable carbides are considered. Thermodynamic parameters that ensure the stability of solid phases are determined. Thermodynamic analysis with the participation of carbides in the process of solid-phase reduction was performed. Features of the carbido-thermal reduction mechanism are considered. The introduction of metallic iron into the charge creates the preconditions for the reduction of carbon, as well as intensifies the process of solid-phase reduction. The results of the performed researches testify to the fundamental possibility of complete reduction of Cr2O3 in the presence of iron rather quickly. The metallized product obtained under these conditions is largely susceptible to decarburization. Calculations show that at a ratio of Cr2O3 and carbon in the charge and an atomic ratio of Cr/Fe ≈ 1, the carbon content in the final product is ~ 4.5%. The charge mixture in principle allows to reduce the carbon concentration to ~ 2.8%. Replacing iron with iron oxides does not reduce the speed characteristics of the process. It should be noted that the replacement of Cr2O3 by natural material is accompanied by a significant reduction in the rate of recovery. The influence of some parameters on the speed characteristics of carbido-thermal reduction of chromium-containing materials is analyzed.

Boosting Capacitive Deionization Performance of Commercial Carbon Fibers Cloth via Structural Regulation Based on Catalytic‐Etching Effect

Monolithic carbon electrodes with robust mechanical integrity and porous architecture are highly desired for capacitive deionization but remain challenging. Owing to the excellent mechanical strength and electroconductivity, commercial carbon fibers cloth demonstrates great potential as high‐performance electrodes for ions storage. Despite this, its direct application on capacitive deionization is rarely reported in terms of limited pore structure and natural hydrophobicity. Herein, a powerful metal‐organic framework‐engaged structural regulation strategy is developed to boost the desalination properties of carbon fibers. The obtained porous carbon fibers features hierarchical porous structure and hydrophilic surface providing abundant ions‐accessible sites, and continuous graphitized carbon core ensuring rapid electrons transport. The catalytic‐etching mechanism involving oxidation of Co and subsequent carbonthermal reduction is proposed and highly relies on annealing temperature and holding time. When directly evaluated as a current collector‐free capacitive deionization electrode, the porous carbon fibers demonstrates much superior desalination capability than pristine carbon fibers, and remarkable cyclic stability up to 20 h with negligible degeneration. Particularly, the PCF‐1000 showcases the highest areal salt adsorption capacity of 0.037 mg cm−2 among carbon microfibers. Moreover, monolithic porous carbon fibers‐carbon nanotubes with increased active sites and good structural integrity by in‐situ growth of carbon nanotubes are further fabricated to enhance the desalination performance (0.051 mg cm−2). This work demonstrates the great potential of carbon fibers in constructing high‐efficient and robust monolithic electrode for capacitive deionization.

Process Development for Integrated Use of Metallurgical Production Wastes

A physicochemical mechanism was studied for carbon thermal reduction of zinc and iron oxides from blast furnace slurries as well as from gas cleaning unit dusts of steelmaking furnaces. With the use of the kinetic analysis the optimal conditions were defined for the carbon thermal reduction as well as the initial data for the development of the joint carbon thermal reduction processes of zinc and iron oxides. An appropriate and clean process was developed; it allows pellet production from zinc containing dusts and their processing in a rotating furnace with an almost complete zinc rundown and trapping in the hose filters; while the metallic iron remaining in the pellets may be used for conversion. The data obtained through the industrial testing confirms the appropriateness of the process implementation and allows the cost effectiveness analysis of the zinc containing dust reclaiming.

C/Sn deposition on a helical carbon nanofiber matrix as a high performance anode for lithium-ion batteries

C/Sn/HCNF composites were successfully prepared by solution phase synthesis and carbon thermal reduction. Within the hybrid composite, the HCNFs, Sn and carbon layer show a synergistic effect in improving coulombic efficiency and electrical capacity.

Study on a new process and its kinetics of iron recovery and glass-ceramics preparation from desulfurization slag

This paper creatively proposes a new process with desulfurization slag leached by ammonium chloride as pretreatment, and the main point of this paper lies in the processing of desulfurization residue leached by ammonium chloride. Through component analysis the formula is adjusted with high aluminum coal ash and glass cullet, making the melting point of the reduction slag around 1200?, which facilitates the separation of iron and slag. At the same time, the reduction slag is adjusted to the target crystallization phase, so that the high temperature reduction slag after carbon thermal reduction can be used to produce glass-ceramics directly. The results show that iron recovery rate is over 99%, and diopside and nepheline glass-ceramics are produced, which shows that the new process is feasible. However, the crystal growth index is less than 3, which means that the crystallization capacity of the glass-ceramics is low, and nucleating agent is needed in the preparation of glass-ceramics.

Recycling of Valuable Metals from Spent Lithium-Ion Batteries by Membrane-Pyrolysis Assisted Carbon Thermal Reduction

Recycling of Valuable Metals from Spent Lithium-Ion Batteries by Membrane-Pyrolysis Assisted Carbon Thermal Reduction

Product control and a study of the structural change process during the recycling of lithium-ion batteries based on the carbothermic reduction method

Carbothermal reduction to recover lithium-ion batteries is an environmentally friendly recycling method. This work provides a theoretical analysis of the thermodynamics and an experimental verification process for the carbon thermal reduction recovery of lithium cobaltate (LiCoO2), as well as an explanation of the microstructural changes. The reaction conditions are controlled to obtain the ideal recovery product. A thermodynamic graph of the possible reaction between LiCoO2 and graphite (C) and the reduction of cobalt oxide (CoO, Co2O3, Co3O4) by carbon monoxide (CO) is obtained by thermodynamic analysis. The feasibility of the carbothermic reduction reaction of LiCoO2 at high temperature is studied under standard atmospheric pressure. By controlling the reaction temperature (800 °C) and the ratio of the reactants (LiCoO2/C = 4:5), the reduction products cobalt monoxide (CoO) and lithium carbonate (Li2CO3) are obtained, and the recovery rates are 89% and 84%, respectively. From the perspective of the crystal structure, the reduction process of LiCoO2 is analyzed. The Li-O bond in the LiCoO2 crystal structure is destroyed by CO, which promotes destruction of the Li-O octahedral structure and the formation of a Co-O octahedron. The Li-O octahedron is transformed into a tetrahedral structure in Li2O, and Li2O then reacts with CO2 to form Li2CO3; the Co-O octahedrons combine to form a CoO crystal structure. When the temperature continues to rise, CoO is reduced to Co. The carbothermic reduction recovery method does not require any additional hazardous chemicals and can avoid secondary pollution during the recovery process. This research provides theoretical support for the industrial recycling of lithium-ion batteries.

Recycling of chrysotile-asbestos production waste

The article examines results of studies on the effect of temperature, amount of carbon and pressure on the possibility of obtaining iron silicides and gaseous magnesium by carbon-thermal reduction of silicon and magnesium oxides containing in chrysotile-asbestos waste products. The studies were carried out using the HSC-6.0 software package (Outokumpy) and the second-order rotatable designs (Box-Hunter plans). It has been established that technology allows us to increase αSi(al), for example, at 1400 °C from 89.6 to 96.75%, reduce undesirable losses of silicon with gaseous SiO from 8.97 to 2.08% and slightly increase αMg(gas) from 97.41 to 97.54%. The alloy formed at 1300 °C contains 28.7% of silicon and corresponds to FS25 grade ferrosilicon.

New understanding on metal recovery of Fe, Ni and Cr during carbon-thermal reduction of stainless steel dust

Stainless steel dust is a typical solid waste from iron and steel smelting. In this study, valuable metal components were recovered from stainless steel dust by carbon-thermal reduction. The effect of reduction conditions on the recovery of Fe, Ni and Cr was studied. The restrictive steps of Fe, Ni and Cr in the reduction process were clarified by XRD and SEM. The results show that the reduction temperature has a great influence on the reduction of metal Fe, Ni and Cr in stainless steel dust, and the increase of reduction temperature, reduction time and appropriate carbon ratio promoted the recovery of metal. The intermediate phase fayalite (Fe,Ni)2SiO4 and magnesiochromite Cr2MgO4 in the reduction process are the restrictive factors that cause the low recovery of Fe, Ni and Cr metals. In the process of carbon-thermal reduction, with the increase of reduction time, Fe2+ and Ni2+ in mesophase (Fe, Ni)2SiO4 were replaced by Mg2+ and Ca2+ in MgO and CaO, and finally reduced to MgCaSiO4; Cr3+ in the mesophase Cr2MgO4 was replaced by Al3+ in Al2O3 and finally reduced to Al2MgO4, which improves the recovery of metal Fe, Ni and Cr.