Reduction Of Zinc Oxide Research Articles

Reduction of electric arc furnace dust pellets by simulated reformed natural gas

The purpose of this paper is to study the kinetic reaction of electric arc furnace dust pellets using a reducing gas simulating the reformed natural gas. The kinetic investigation was accomplished via forced stepwise isothermal analysis method. The tests were programmed in the range of 500–1000 °C. It was used a reducing gas contained 25 % of CO and 75 % of H2. X-ray patterns were analyzed in order to understand the reduction process. The results show the reduction of electric arc furnace dust pellet occurs in three steps. At 550–650 °C, the zinc ferrite is reduced to magnetite and zinc oxide, followed by the reduction of magnetite to wustite. Carbon deposition on the pellet surface was detected in this step, which impairs the kinetic analysis. In the range of 700–800 °C, wustite is reduced to iron. It was determined a mixed control between nucleation and diffusion with E a of 89.2 kJ mol−1. At 850–950 °C, the main reaction is zinc oxide reduction to gaseous zinc. However, wustite reduction is also observed. The E a of 135.5 kJ mol−1 with a mixed control between diffusion and chemical reaction was detected.

Effect of magnesium on the aluminothermic reduction rate of zinc oxide obtained from spent alkaline battery anodes for the preparation of Al–Zn–Mg alloys

The aluminothermic reduction of zinc oxide (ZnO) from alkaline battery anodes using molten Al may be a good option for the elaboration of secondary 7000-series alloys. This process is affected by the initial content of Mg within molten Al, which decreases the surface tension of the molten metal and conversely increases the wettability of ZnO particles. The effect of initial Mg concentration on the aluminothermic reduction rate of ZnO was analyzed at the following values: 0.90wt%, 1.20wt%, 4.00t%, 4.25wt%, and 4.40wt%. The ZnO particles were incorporated by mechanical agitation using a graphite paddle inside a bath of molten Al maintained at a constant temperature of 1123 K and at a constant agitation speed of 250 r/min, the treatment time was 240 min and the ZnO particle size was 450-500 mesh. The results show an increase in Zn concentration in the prepared alloys up to 5.43wt% for the highest initial concentration of Mg. The reaction products obtained were characterized by scanning electron microscopy and X-ray diffraction, and the efficiency of the reaction was measured on the basis of the different concentrations of Mg studied.

Continuous Solar Carbothermal Reduction of Aerosolized ZnO Particles Under Vacuum in a Directly Irradiated Vertical-Tube Reactor

A solar-driven aerosolized particle reactor under vacuum was tested for carbothermal reduction of zinc oxide using concentrated solar power. The reactor concept is based on the downward flow of zinc oxide and carbon particles, which are indirectly heated by an opaque intermediate solar absorption tube. The particles are rapidly heated to reaction temperature and reduced within residence times of less than 1 s. In the continuous feeding experiments, maximum sustained temperatures close to 2000 K and heating rates as fast as 1400 K min−1 could be achieved for pressures between 1 and 1000 mbar. Reactant conversions of up to 44% were obtained at 1000 mbar. It was found that a reduction in system pressure leads to a decreased particle residence time (as low as 0.09 s), and therefore low conversion (as low as 1%), thus partially diminishing the positive thermodynamic effects of vacuum operation. Experimental results validate the robust and versatile reactor concept, and simultaneously highlight the necessity of balancing the system design in order to optimize the conflicting influence of vacuum operation and reacting particle residence time.

Thermodynamic analysis of the carbothermic reduction of electric arc furnace dust in the presence of ferrosilicon

Thermodynamic analysis of zinc recovery from electric arc furnace (EAF) dust by carbon in the presence of ferrosilicon was studied. A preheating process was performed to remove volatile compounds from dust to avoid impurities in the final zinc product. The main process includes reduction of zinc oxide and gasification and condensation of zinc vapor. Equilibrium condition was computed using FactSage program for the processes of reduction and gasification. The effect of ferrosilicon addition on the recovery of zinc was investigated for the temperature range of 950–1050°C at the constant pressure of one atmosphere. It is shown that ferrosilicon provides a better kinetic condition for zinc recovery by facilitating slag formation. The preferred condition for formation of liquid slag was predicted based on thermodynamic calculations and verified by performing some experiments. The experimental results show that good agreement between calculations and experiments can be obtained with higher amounts of silicon contents and at higher temperatures where liquid slag is presented. A mixture of the dust with 10% C and 7% FeSi(75%) can be used to achieve over 97% zinc recovery.

Synthetic zinc ferrite reduction by means of mixtures containing hydrogen and carbon monoxide

Solid waste generation is one of the main problems in the steelmaking process. One of the most problematic waste products is the electric arc furnace dust, which is a by-product rich in iron and zinc and is present as zincite (zinc oxide) or franklinite (zinc ferrite). This work focuses on the reduction kinetics of synthetic zinc ferrite by gases containing hydrogen and carbon monoxide. This process was examined via forced stepwise isothermal analysis. The test was conducted at temperatures ranging from 500 to 950 °C. Reduction of zinc was accomplished using a mixture of hydrogen and carbon monoxide in order to simulate reformed natural gas. The results indicated that reduction of zinc ferrite occurred in two stages (550–750 °C and 800–900 °C). The first stage was characterized by iron oxide reduction, where a mix control between nucleation and diffusion was determined. The apparent activation energy obtained was 71.5 kJ mol−1. The second stage was characterized by zinc oxide reduction, where the controlling mechanism was identified as a mixed control between diffusion and phase boundary reaction. The apparent activation energy was 135.5 kJ mol−1. The formation of a dense layer of metallic iron around the unreacted core may have caused the apparent activation energy to increase.

Electrochemical Kinetics of Reduction of Zinc Oxide to Zinc Using 2:1 Urea/ChCl Ionic Liquid

Electrochemical reduction of zinc oxide to zinc was investigated in 2:1 urea/choline chloride electrolyte at applied cell potentials of 3.2 - 3.5V. Concentration polarization was observed at the beginning of electrochemical reduction process. The diffusion coefficient of zinc species in the electrolyte was calculated to be 7.85×10−13m2/s at 363K. An increase in the current density was observed after a sharp initial decrease due to activation polarization, in which case, a linear relationship was established between log (current density) and over-potential. The electrochemical kinetic parameters was investigated in the steady-state current region. The transfer coefficient was calculated to be 0.2 indicating an irreversible charge transfer process. The XRD analysis confirmed that the electrodeposits consists of high purity zinc. The SEM analysis showed the formation of dendrites at higher over-potential (≥0.65V), which is comparable to the calculated critical over-potential for Zn dendrite formation. The estimated energy consumption varied from 3.04 to 3.66 kWh/kg and current efficiency from 78.5 to 88.9%.

Briquetting of EAF Dust for its Utilisation in Metallurgical Processes

Abstract Dust generated at an electric arc furnace during steel production industry is still not a solved problem. Electric arc furnace dust (EAF) is a hazardous solid waste. Sintering of well-prepared briquetted mixtures in a shaft furnace is one of possible methods of EAFD utilisation. Simultaneously some metal oxides from exhaust gases can be separated. In this way, various metals are obtained, particularly zinc is recovered. As a result, zinc-free briquettes are received with high iron content which can be used in the steelmaking process. The purpose of the research was selecting the appropriate chemical composition of briquettes of the required strength and coke content necessary for the reduction of zinc oxide in a shaft furnace. Based on the results of the research the composition of the briquettes was selected. The best binder hydrated lime and sugar molasses and the range of proper moisture of mixture to receive briquettes of high mechanical strength were also chosen and tested. Additionally, in order to determine the thermal stability for the selected mixtures for briquetting thermal analysis was performed. A technological line of briquetting was developed to apply in a steelworks.

On the Development of a Zinc Vapor Condensation Process for the Solar Carbothermal Reduction of Zinc Oxide

In the conventional Imperial Smelting Process, the dominating pyrometallurgical zinc production process, zinc vapor is recovered from the furnace off-gas by absorption into an intense spray of molten lead droplets in a splash condenser, followed by separation of zinc from the Zn-Pb alloy upon cooling from 550°C to 450°C by taking advantage of the decrease in the solubility of zinc in lead at lower temperatures. The adaptation of this condenser technology into a solar-driven thermochemical plant using concentrated solar energy faces several drawbacks owing to its mechanical complications and the continuous recirculation of large quantities of lead. An alternative zinc condenser concept involving gas bubbling through a zinc liquid bath of the off-gas evolved from the carbothermal reduction of ZnO is thus proposed and numerically modeled for transient heat and mass transfer. Condensation of bubbles containing 53.5% of noncondensable gases yielded chemical conversions of Zn(g) to Zn(l) in the range of 95.6–99.8% for operation in the temperature range 500–650°C while conversions of Zn(g) to ZnO in the order of 10−6 were obtained, thus predicting successful suppression of Zn(g) reoxidation by CO2 and CO.

Plasma in-liquid method for reduction of zinc oxide in zinc nanoparticle synthesis

Metal air-batteries with high-energy density are expected to be increasingly applied in electric vehicles. This will require a method of recycling air batteries, and reduction of metal oxide by generating plasma in liquid has been proposed as a possible method. Microwave-induced plasma is generated in ethanol as a reducing agent in which zinc oxide is dispersed. Analysis by energy-dispersive x-ray spectrometry (EDS) and x-ray diffraction (XRD) reveals the reduction of zinc oxide. According to images by transmission electron microscopy (TEM), cubic and hexagonal metallic zinc particles are formed in sizes of 30 to 200 nm. Additionally, spherical fiber flocculates approximately 180 nm in diameter are present.

Numerical Investigation of a Metal-oxide Reduction Reactor for Thermochemical Energy Storage and Solar Fuel Production

The optimum design of a thermochemical reactor involves complex phenomena such as radiation heat and mass transfer, reaction kinetics, and fluid-solid interactions which makes the process to be cumbersome. The computational modelling using computational fluid dynamics (CFD) is an important tool to study, analyse, interpret and optimize such a complex system. The present study has developed a CFD model using Ansys-Fluent 14.0. The model employs the Eulerian-Lagrangian approach with the chemical reactions for a vertical axis thermochemical reactor for Zinc oxide reduction process. The conversion efficiency and temperature distributions for Zinc oxide reduction estimated by the CFD results have been validated with the published results by the PROMES CNRS laboratory (France) for a horizontal reactor design. The effect of particle size and gravity with a view to adapt it for a vertical beam-down solar concentrator have been analysed in the present study. It was observed that smaller particles provide higher surface area for enhanced heat transfer. Gravitational effects turned to be significant as the particle size increases. The model will assist in the effort of developing an efficient solar chemical reactor, for innovative thermochemical energy storage systems or fuel production, which will be tested at the Masdar Institute‘s beam down research facility.

Mathematical simulation of direct reduction process in zinc-bearing pellets

A one-dimensional unsteady mathematical model was established to describe direct reduction in a composite pellet made of metallurgical dust. The model considered heat transfer, mass transfer, and chemical reactions including iron oxide reductions, zinc oxide reduction and carbon gasification, and it was numerically solved by the tridiagonal matrix algorithm (TDMA). In order to verify the model, an experiment was performed, in which the profiles of temperature and zinc removal rate were measured during the reduction process. Results calculated by the mathematical model were in fairly good agreement with experimental data. Finally, the effects of furnace temperature, pellet size, and carbon content were investigated by model calculations. It is found that the pellet temperature curve can be divided into four parts according to heating rate. Also, the zinc removal rate increases with the increase of furnace temperature and the decrease of pellet size, and carbon content in the pellet has little influence on the zinc removal rate.

Numerical investigation of thermal disassociation of ZnO for hydrogen production: Parametric study and reactor configuration

SUMMARY The present research is focused on the two-step ZnO/Zn thermochemical water splitting cycle for hydrogen production. In the present paper, the numerical modeling of the first step, which involves endothermic reduction of zinc oxide (ZnO), is carried out in a cylindrical reactor using Computational Fluid Dynamics (CFD). The parametric study shows that the fractional conversion of ZnO increases with an increase in the flow rate of ZnO, while it decreases with an increase in the ZnO particle diameter and carrier gas mass flow rate. Six different reactor configurations are also assessed comprehensively. It is observed that a cylindrical reactor with a tangential inlet at the top plane and a tangential outlet at the bottom plane has higher robustness to the variation of various operating parameters with consistently high ZnO fractional conversion. Copyright © 2013 John Wiley & Sons, Ltd.

In situ vacuum thermal mass spectroscopy for the selection of an environmentally friendly, energy saving catalytic additive and optimization of the process by a novel ignition mechanism

We report herein the utilization of vacuum thermal mass spectrometry (VTMS) for the selection of an environmentally friendly, energy saving catalytic additive and a novel ignition mechanism, which is complementary to catalysis for the reduction of zinc oxide with carbon.

Computational Fluid Dynamics (CFD) Investigation of Submerged Combustion Behavior in a Tuyere Blown Slag-fuming Furnace

A thin-slice computational fluid dynamics (CFD) model of a conventional tuyere blown slag-fuming furnace has been developed in Eulerian multiphase flow approach by employing a three-dimensional (3-D) hybrid unstructured orthographic grid system. The model considers a thin slice of the conventional tuyere blown slag-fuming furnace to investigate details of fluid flow, submerged coal combustion dynamics, coal use behavior, jet penetration behavior, bath interaction conditions, and generation of turbulence in the bath. The model was developed by coupling the CFD with the kinetics equations developed by Richards et al. for a zinc-fuming furnace. The model integrates submerged coal combustion at the tuyere tip and chemical reactions with the heat, mass, and momentum interfacial interaction between the phases present in the system. A commercial CFD package AVL Fire 2009.2 (AVL, Graz, Austria) coupled with several user-defined subroutines in FORTRAN programming language were used to develop the model. The model predicted the velocity, temperature field of the molten slag bath, generated turbulence and vortex, and coal use behavior from the slag bath. The tuyere jet penetration length (l P) was compared with the equation provided by Hoefele and Brimacombe from isothermal experimental work $$ \left( {\frac{{l_{\text{P}} }}{{d_{o} }} = 10.7\left( {N^{\prime }_{Fr} } \right)^{0.46} \left( {\rho_{\text{g}} /\rho_{l} } \right)^{0.35} } \right) $$ and found 2.26 times higher, which can be attributed to coal combustion and gas expansion at a high temperature. The jet expansion angle measured for the slag system studied is 85 deg for the specific inlet conditions during the simulation time studied. The highest coal penetration distance was found to be l/L = 0.2, where l is the distance from the tuyere tip along the center line and L is the total length (2.44 m) of the modeled furnace. The model also predicted that 10 pct of the injected coal bypasses the tuyere gas stream uncombusted and carried to the free surface by the tuyere gas stream, which contributes to zinc oxide reduction near the free surface.

Kinetic investigations of two processes for zinc recovery from zinc plant residue

This paper presents a kinetic study of hydrometallurgical and pyrometallurgical processes employed for the recovery of zinc from a zinc plant residue (ZPR). The hydrometallurgical process investigated involved zinc leaching from the ZPR with sulphuric acid solution, while the pyrometallurgical process was based on zinc oxide reduction from the ZPR using activated carbon as the reducting agent. At the optimum leaching conditions, the zinc recovery was 89·5% at 95°C after 60 min. The data obtained for the leaching kinetics indicated that the dissolution of ZPR is a diffusion controlled process and the activation energy is equal to 21±2 kJ mol−1. The maximum zinc recovery, obtained during pyrometallurgical treatment was 72% at 1300°C after 60 min. Kinetic investigations revealed that the zinc oxide reduction is carried out in the transient kinetic area, where both diffusion and the chemical reaction control the overall process rate, with an activation energy of 38±5 kJ mol−1.Cet article présente une étude cinétique d'un procédé hydrométallurgique et d'un procédé pyrométallurgique utilisés pour la récupération du zinc du résidu d'une usine de zinc (ZPR). Le procédé hydrométallurgique investigué impliquait la lixiviation du zinc du résidu de l'usine de zinc avec une solution d'acide sulfurique, alors que le procédé pyrométallurgique était basé sur la réduction de l'oxyde de zinc du résidu de l'usine de zinc en utilisant du charbon activé comme agent de réduction. Aux conditions optimales de lixiviation, la récupération du zinc était de 89·5% à 95°C après 60 min. Les données obtenues pour la cinétique de lixiviation ont indiqué que la dissolution du résidu de l'usine de zinc était un procédé contrôlé par la diffusion et l'énergie d'activation est égale à 21±2 kJ mol−1. La récupération maximale de zinc, obtenue lors du traitement pyrométallurgique, était de 72% à 1300°C après 60 min. Les investigations de la cinétique ont révélé que la réduction de l'oxyde de zinc était effectuée dans la zone de cinétique transitoire, où tant la diffusion que la réaction chimique contrôlent la vitesse globale du procédé, avec une activation d'énergie de 38±5 kJ mol−1.

Heliostat field layout optimization for high-temperature solar thermochemical processing

The layout of the heliostat field of solar tower systems is optimized for maximum annual solar-to-chemical energy conversion efficiency in high-temperature thermochemical processes for solar fuels production. The optimization algorithm is based on the performance function that includes heliostat characteristics, secondary optics, and chemical receiver–reactor characteristics at representative time steps for evaluating the annual fuel production rates. Two exemplary applications for solar fuels production are selected: the thermal reduction of zinc oxide as part of a two-step water-splitting cycle for hydrogen production, and the coal gasification for syngas production.

Study on Deactivation of Zinc-Based Sorbents for Hot Gas Desulfurization

The possible reasons that were associated with the reduction of zinc oxide and the deposition of elemental Zn on the zinc-based sorbent surfaces were proposed in this study and examined by monitoring chemical reactivity and physical/chemical properties of the sorbents during the multicyclic tests with the aid of various diagnostics in order to investigate the deactivation of the sorbents that was observed in previous works. The reactivity of the sorbents was investigated using a temperature programmed technique (TPT) with a thermal gravimetric analyzer (TGA). From our experiments, the undesirable features due to the reduction of ZnO that was caused by the reducing components in the gasified coal gas were observed in the chemical reactivity and sorbent properties. In the investigation of the migration of elemental Zn onto the sorbent surface, elemental Zn accumulated on the surface of the sorbents rather than the zinc vaporization. It might have caused the deactivation of the zinc-based sorbents.

Real time monitoring of chemical transformations during catalytic reduction using gas source mass spectrometry: carbon/zinc carbonate hydroxide

We report herein the utilization of a vacuum reduction distillation system (VRDS) coupled with mass spectrometry (MS) to characterize chemical transformations in thermal analysis. The system initially designed to monitor metal purification by distillation is applied for the first time to the catalytic reaction of in situ formed nickel oxide during the carbothermic reduction of zinc oxide.1

Kinetics of the reactions of carbon containing zinc oxide composites under microwave irradiation

As a fundamental study for the recycling of EAF dust using microwave heating, the reduction rate of a zinc oxide composite by solid carbon under microwave irradiation was investigated. It was found that the reduction of zinc oxide by solid carbon under microwave irradiation was much faster than the conventional method, and the activation energy for the reaction under microwave irradiation was estimated to be 335 kJ/mol.

Dynamics and control of solar thermochemical reactors

Abstract A general dynamic model for solar-driven thermochemical processes is formulated based on unsteady mass and energy conservation equations coupled to the reaction kinetics. It is applied to two pertinent high-temperature thermochemical reactors for fuel production that make use of concentrated solar energy as the source of process heat, namely: an indirectly irradiated batch-operated packed bed reactor for the carbothermic reduction of zinc oxide, and a directly irradiated continuously operated particle flow reactor for the steam-gasification of petcoke. Model parameter identification and validation is accomplished by comparing numerically simulated and experimentally measured temperatures and outlet product concentrations. A linear feedback controller was implemented using the LQG/LTR design method. Simulations of the controlled reactor system with real solar irradiation data indicates improved quality and steadiness of product composition throughout transient solar input phases and superior solar-to-chemical energy conversion efficiency.