Dross Particles Research Articles

Iron oxides in the beach sediments of the North-Western part of the Sea of Azov

The morphological features and chemical composition of iron oxides in the beach deposits of the northwestern part of the Sea of Azov were studied on the basis of research materials of 2016-2020, using a scanning electron microscope with an integrated electron-probe analysis system. The chemical composition of iron oxides varies from Fe39O86 to Fe17O8. Most of the individuals surveyed are stoichiometric iron (III) oxide Fe2O3, but only a few of them have morphological features of the natural hematite, usually martite. The vast majority of Fe2O3 individuals and other individuals in the whole range of the chemical composition have specific morphological features of technogenic compounds and generally are ferrous dross particles formed during the rolled steel process. The sharp predominance of the technogenic component of iron oxides in the black sands is an important fact that witnesses the powerful man9made pressure on the ecosystems of the Azov Sea.

CFD-DEM simulations of a stirred liquid bath containing particles based on a theoretical scaling framework

BackgroundCoupled computational fluid dynamics-discrete element method (CFD-DEM) simulations are valuable tools for studying particle-fluid coupling problems. However, because of the many particles involved, full-scale simulations are not feasible. MethodsA theoretical scaling framework developed in our previous work was introduced for the first time in the CFD-DEM simulations. A 1/2 scaled-down numerical model was established based on the physical model used to observe the dynamic behavior of dross particles in a hot-dip galvanizing bath. The applicability of the theoretical scaling framework for the CFD-DEM simulations was demonstrated by comparing the results of the physical and scaled-down numerical models. Additionally, the effects of the belt width and velocity on the flow field and dynamic behavior of the particles were investigated. Significant findingsThe results show that the evolution of the particle-accumulation morphology at different belt widths in scaled-down simulations agreed with that in physical model experiments, confirming that the theoretical scaling framework can be used in CFD-DEM simulations and is advantageous in significantly reducing number of particles required for the simulations. As the belt speed decreased, the number of suspended particles also decreased. Furthermore, a reduction in the belt width led to a shift of the aggregation region of the suspended particles away from the vicinity of the symmetrical plane of the bath toward the sidewalls. This shift of the aggregation region was beneficial in preventing the adhesion of dross particles to the surface of the steel strip during the hot-dip galvanizing process.

Thermodynamics-CFD-DPM modeling of dross formation and diffusion in a Zn-0.3Al galvanizing bath

In order to further reduce the production cost and enhance product of steel strip marketing competitiveness, industrial enterprises will choose to increase production rate, leading to the more dross generation. This paper proposes a numerical simulation based on thermodynamics, computational fluid dynamics (CFD) and discrete particle method (DPM) to simulate the η-Fe2Al5 dross formation distribution, and to track the trajectories of different sized dross particles in a Zn-0.3Al galvanizing bath. An optimized modeling of interfacial reactions involving the instantaneous rate of iron dissolution and aluminum uptake is firstly set up and validated with the previous experimental results and theoretical calculation. On the basis of the analysis on interfacial reaction, a potential influence factor (strip velocity) is discussed. The results show that higher strip velocity will result in much more η-Fe2Al5 dross around the strip entry side and the average dross formation within the V-typed region increases with the increase of the strip velocity due to the higher dissolved Fe concentration in molten zinc. Additionally, the trajectories of dross particles are discussed by injecting particles in the specific generation area. It can be concluded that the η-Fe2Al5 is likely to adhere to the steel-strip and roll surface. Furthermore, the trajectories of the dross particles are affected significantly by the flow of zinc and the particle size, thus the trajectories of particles resemble the streamlines. The average residence time of the suspended dross particles in the outer area of steel strip exit is longest. It is illustrative that the dross build-up region is the front wall area of the zinc pot.

Phase Stability of Dross Particles in Hot-Dip Zn-55wt%Al-1.6wt%Si Galvanizing Bath.

Dross in a Zn-55wt%Al-1.6wt%Si metal coating bath is a mixture of bath metal and the quaternary intermetallic phase τ5c-Al20Fe5Si2(+Zn). Understanding the properties and formation of dross in a hot-dip Al-Zn galvanizing bath at the processing temperature (~600 °C) is critical for improving the production quality of steel sheet coating. However, dross analysis is usually conducted at room temperature with dross samples taken from the hot-dip bath and it is not known how representative these samples are of the phase(s) existing at high temperature. Using in-situ synchrotron X-ray diffraction (XRD), the crystal lattice and the coefficient of thermal expansion (CTE) of the intermetallic phase have been determined in the temperature range of 30 °C to 660 °C. Phase formation and phase stability of the intermetallic phase in the dross powder have been determined, providing fundamental knowledge for optimizing the production and quality of steel sheet coating.

An Energy Saving Option for Production of pure α – Alumina for Industrial Applications Using Waste Aluminium Dross

Globally, over four million tonnes of aluminium dross are reportedly produced throughout the world each year, in which about 95% of this material is land-filled. This material represents a major waste from primary and secondary aluminium production that contain about 15 to 70% recoverable metallic aluminium that can be extracted and later used for industrial and engineering purposes.In this study, the production of alumina from aluminium dross via leaching-cum-precipitation route for other industrial purposes was examined. Arrangement of elements, compounds present within the aluminium dross particle size -150 + 70 μm was initially determined by X-ray Fluorescence (XRF), X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) to give basis for explaining the dissolution process of aluminium the intermediate material for alumina production. The results obtained showed that 99% of aluminium was leached out using -150+78 mesh ore particle size at a reaction temperature of 60°C for 60 min reaction time with 1.5 M hydrochloric acid. The morphology analysis of the produced alumina at optimal leaching by XRD showed that it contains α-alumina (α-Al2O3) and hydrated hydroxyl molecule (OH) as the major compound.

Reversible Reaction Kinetics Model for the Formation of Dross Particles in Hot-Dip Galvanizing Lines

Reversible Reaction Kinetics Model for the Formation of Dross Particles in Hot-Dip Galvanizing Lines

Preparation of Aluminum Dross Non-Fired Bricks with High Nitrogen Concentration and Optimization of Process Parameters

In order to solve the difficulties in the utilization of aluminum dross resources, non-fired bricks with aluminum dross with high nitrogen concentration as the main raw material were prepared. Three process parameters, including forming pressure, mixing-water amount, and aluminum dross particle size, were subjected to single-factor experiments. Based on the response surface method, a mathematical model was established between the process parameters and the non-fired bricks’ compressive properties, which were subjected to ANOVA. The process parameters were optimized and then verified experimentally. According to the results, the established regression model is able to accurately predict the compressive properties of non-fired bricks. The difference between the experimental value and the model’s predicted value was only 0.36%. The optimal process parameters for aluminum dross to prepare non-fired bricks are as follows: forming pressure is 18 MPa, mixing-water amount is 15% and particle size range is 80–130 mesh. The compressive strength of the prepared non-fired bricks is 24.66 MPa, which meets the requirement of MU20 non-fired bricks in Non-fired Rubbish Gangue Bricks.

Hydrodynamically driven facet kinetics in crystal growth

In this paper we show that the presence of liquid flow around a crystal growing from melt can induce dissymmetry in growth similar to that described by anisotropic interfacial kinetic coefficients. A front tracking interface model based on a cellular automaton approach was applied to the growth of a Fe2Al5 crystal (also known as top dross particle) in a saturated Zn melt at constant temperature. The growth rate was found to be influenced by the intensity of the melt flow and by the direction of the flow with respect to the crystal orientation. The magnitude and the direction of flow modify the diffusion boundary layer, changing the conditions (temperature and concentration) at the facet interface, therefore the mass transfer. We have shown that despite the isotropy of interfacial kinetics, hydrodynamics was able to introduce an anisotropy in the crystal growth similar to the natural anisotropy in interfacial kinetics of the facets. The facets grow rate was found to be strongly dependant on the Reynolds number as well as on the orientation of the crystalline orientation with respect to the flow direction.

Trajectory of Top-Dross Particles During the Melting of Zinc Ingot in Galvanizing Pot

The production of hot-dip galvanized steel presents great challenges, because it is currently the main raw material in the manufacturing of automobiles, and its surface quality is fundamental for the construction of automobiles. Obtaining the best surface appearance in galvanized steels is directly related to understanding the phenomena involved in the galvanizing process. In this process, achieving thermal and chemical stability of the galvanizing pot means keeping top-dross formation under control. The top-dross is the main problem to be controlled, because it impacts the surface quality of coated steel. Some studies have been conducted to understand the formation of top-dross particles into the zinc bath, but little is known about the path of the particles formed from the melting ingots. In this study, the trajectories of these particles were simulated. It has been found that, depending on the immersion depth, dross particles may have different destinations.

Crystal Structure Analysis of Top Dross in Molten Zinc Bath by First Principles Calculation and Synchrotron X-ray Diffraction

In a molten zinc bath in a continuous galvanizing line, the top dross particles crystallize as a Zn-containing intermetallic Fe2Al5 compound, which generates surface defects in the final product by easily adhering to the steel sheets. The present study focused on analysis of the crystal structure of a top dross by first principles calculation and synchrotron X-ray diffraction of the top dross prepared in a laboratory. The following results were obtained: first principles calculation on the top dross suggested that two Al atoms at four of the partially occupied Al sites in the Fe2Al5 structure proposed by Mihalkovič et al., were replaced by two Zn atoms. In addition, the Al atoms at both the types of partially occupied Al sites in Fe2Al5 proposed by Burkhardt et al., were equally replaced by Zn atoms. The proposed crystal structure of the top dross was verified by conducting X-ray diffraction profile analysis using RIETAN-FP simulations as well as the experimentally determined lattice constant of the Zn-containing top dross.

Numerical Simulation of Zinc Flow in Different Layouts of Galvanization Pot

The production of galvanized steel with zinc (GI) presents great challenges due to the high demand for surface quality required for its applications. The automotive segment is one of the largest consumers of this type of product. In hot dip galvanizing lines, the main defect that affects the surface quality of the coatings is the dragging of dross particles. Some studies have already been carried out to understand the formation of these particles inside the zinc bath, however little is known about the trajectory of these particles in relation to the pot layout. In this study, two types of layout were simulated to assess how this interferes with the flow of zinc. In the results it was verified that, the position of the heating inductor significantly modifies the trajectory of the dross particles.

Recovery of zinc from Zn–Al–Fe alloys by gas pressure filtration

The recovery of zinc from galvanizing dross and the removal of iron contained dross particles by gas pressure filtration were investigated using the model of Zn–Fe–Al alloys. The majority of molten zinc was separated after filtration, and the residue intercepted by the filter consisting mostly of dross particles. The effects of the pressure differential (p), separation temperature (T) and alloy composition on the zinc recovery and iron removal were investigated. At p = 0.30 MPa and T = 723 K, 86.2 wt.% zinc was recovered from the Zn–4Al–2Fe alloy, and up to 99.9 wt.% of the iron was concentrated in the residue. Applying a higher pressure differential led to the improved filtration efficiency, and the desired separation temperature was about 723 K. The aluminum content in the Zn–Al–Fe alloy had little effect on separation efficiency, whereas increasing the iron content led to a decrease in the separation efficiency. Our findings demonstrate the potential of the gas pressure filtration method for the recovery of zinc from galvanizing dross.

Impact of hydrodynamics on growth and morphology of faceted crystals

The growth of faceted crystals occurs often in nature and industry, involving often the presence of flow. The growth of faceted crystals is the result of interface kinetics and diffusion phenomenon. The present paper presents a front tracking interface model based on a cellular automaton approach for the simulation of faceted crystal growth. The current model takes into account the interface kinetics and solute transport by diffusion and convection. The propagation of kinks is modelled by differentiating two growth velocities, one normal and one lateral at each face. The positions of the crystal corners are shifted according to growth of adjacent faces. The hydrodynamics is computed with a two-phase model using a penalty method to model the presence of growing obstacles (the crystals). This model was applied in 2D to the growth of hexagonal Fe2Al5 crystals, so called top dross particles, in a saturated liquid at constant temperature. Qualitative comparison was made between simulation and experimental observation of crystal shape and size. The growth rate was found to be strongly influenced by the flow hydrodynamic induced kinetics.

The Evaluation on Corrosion Resistance and Dross Formation of Zn–23 wt% Al–0.3 wt% Si–x wt% Mg Alloy

: A comparative study of the corrosive resistance and dross formation of 55Al–Zn–1.6Si (wt%) (55AZS) and 23Al–Zn–0.3Si–xMg (wt%) (23AZS–xMg, x = 0, 1.5, 3) alloys are performed using immersion corrosion and dross formation test, respectively. The result of immersion corrosion testing shows that corrosive rate of the 23AZS alloy is lower than that of 55AZS alloy in the latter stage of immersion and 23AZS–1.5Mg alloy shows the optimal corrosive resistance compared to other alloys relatively. The result of dross formation test shows that the number of bottom dross particle formed in 23AZS–xMg (x = 0, 1.5, 3) alloy is less than that in 55AZS alloy. Moreover, the thermodynamic calculation is performed to reveal the solubility of Fe in the alloys, the result shows the solubility of Fe reduces as a decrease of Al content in the alloy, and the number of dross particle (Fe4Al13 and 6 (Al9Fe2Si2) phase) generated in 23AZS alloy is more than that in 55AZS alloy. In general, 23AZS–1.5Mg alloy has an advantage of less dross and a certain corrosion resistance and it is expected to be applied for the hot stamping process of coating.

Thermo-chemical Fluid Flow Simulation in Hot-Dip Galvanizing: The Evaluation of Dross Build-Up Formation

This paper presents a new computational framework to investigate the driving force for the formation of intermetallic dross particles in the zinc bath and dross build-up on the bath hardware. This is a major problem in continuous hot-dip galvanizing lines. The Computational Fluid Dynamics (CFD) model calculates the turbulent thermo-chemical flow conditions within the liquid melt. A detailed modeling of the steel strip–liquid interface enhances this approach, by means of a conjugated heat transfer calculation and a spatially resolved, temperature- and concentration-dependent iron dissolution and aluminum uptake. The heart of the computational framework is a thermodynamic model, which assesses the driving force for the formation or dissolution of dross particles in the bath and dross build-up on stationary and rotating equipment. The simulation results are validated with temperature and species depth profile measurements. The applicability of the CFD model is shown by investigating the locally resolved aluminum uptake and iron dissolution at the steel-strip surface, and the multi-physics conditions in the region near the roll. The novel approach of evaluating the thermodynamic driving force enables the assessment of the formation of dross build-up at the roll surface.

Surface Finish and Back-Wall Dross Behavior during the Fiber Laser Cutting of AZ31 Magnesium Alloy.

Magnesium alloys are of increasing interest in the medical industry due to their biodegradability properties and better mechanical properties as compared to biodegradable polymers. Fiber laser cutting of AZ31 magnesium alloy tubes was carried out to study the effect of cutting conditions on wall surface roughness and back-wall dross. During the experiments, an argon gas chamber was adapted in order to avoid material reactivity with oxygen and thus better control the part quality. A surface response methodology was applied to identify the significance of pulse overlapping and pulse energy. Our results indicate minimum values of surface roughness (Ra < 0.7 μm) when the spot overlapping is higher than 50%. A back-wall dross range of 0.24% to 0.94% was established. In addition, a reduction in back-wall dross accumulations was obtained after blowing away the dross particles from inside the tube using an argon gas jet, reaching values of 0.21%. Laser cutting experimental models show a quadratic model for back-wall dross related with the interaction of the pulse energy, and a linear model dependent on pulse overlapping factor for surface roughness.

A promising green process for synthesis of high purity activated-alumina nanopowder from secondary aluminum dross

Abstract More than one million tons of secondary aluminum dross as a hazardous waste are produced by aluminum manufacturers per year throughout the world, which imposes high disposal costs and serious environmental problems. As secondary aluminum dross is considered as an alumina-rich inorganic waste, this study aims to propose a promising approach for clean production of activated-alumina as a widely-used adsorbent, catalyst and catalyst support. In this paper, synthesis and characterization of high crystalline activated-alumina nanopowder from secondary aluminum dross using a novel five-step leaching-based process are presented. To optimize the process, various parameters of dross particle size, leaching time, leaching temperature, acid concentration, and liquid-to-solid ratio were studied using One-Factor-At-a Time approach (OFAT). For the following optimum leaching conditions: particle sizes between 38 and 75 μm, leaching time of 120 min, leaching temperature of 85 °C, acid concentration of 5 M, and the liquid-to-solid ratio of 20 ml/g, the extraction efficiency of alumina was around 83%. The leach liquor was purified by adding 2 N NaOH resulting in sodium aluminate-rich solution. The purified liquor was treated by adding HCl to precipitate Al(OH)3, and the Al(OH)3 was then washed and calcined at 700 °C for 2 h to obtain alumina. Chemical composition, mineralogical phases, chemical bonds, morphology, and particle size distribution of the as-synthesized activated-alumina were determined using X-ray fluorescence (XRF), X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), and dynamic light scattering (DLS), respectively. The as-synthesized activated-alumina exhibited 97.61% purity. Its XRD pattern showed mainly characteristic peaks of gamma phase of alumina. Morphological study by FESEM revealed that the as-synthesized alumina particles have rounded-corner shape. The crystal and average particle size values were about 18.47 and 513 nm, respectively.

Recovery of zinc from galvanizing dross by a method of super-gravity separation

The hot dip galvanizing dross is a valuable by-product because it contains high levels of zinc, motivating a search for processes or technologies to allow the cost-effective recovery of the zinc content. In this work, the feasibility of recovering zinc from an industrial galvanizing dross by a novel method of super-gravity separation was investigated. The effects of gravity coefficient (G), separation time (t) and separation temperature (T) on the separation efficiency were evaluated. When the gravity coefficient was higher than 15, the galvanizing dross samples were separated into two parts, i.e. the upper residue and the lower filtered zinc. The majority of the dross particles were retained in the upper residue and the filtered zinc was purified significantly. At G ≥ 500, t ≥ 180 s and T = 510 °C, over 79 wt% zinc was recovered with a high purity of about 99 wt%. Increasing gravity coefficient and separating time favored the zinc recovery, but at G ≥ 500 and t ≥ 60 s, the zinc recovery increased at a very limited rate. Increasing separating temperature benefited the zinc recovery but reduced the iron removal. Also, cake mode filtration was determined to be the dominant mechanism of the super-gravity separation of galvanizing dross in this work.

Review of Modeling and Simulation of Galvanizing Operations

Worldwide demand for galvanized steel products continues to grow for the assembly of automobile structures that are lighter and more resistant to impact, as well as for applications in the construction and domestic appliance industries. The technical challenges faced by these producers are the ability to coat a variety of low cost, high strength steels in developing a product with minimal surface defects, and reduced consumption of zinc and energy. The performance of the coating process depends on a thorough understanding of the reactions at the steel surface, the bath chemistry, the temperature variation in the bath, and the fluid dynamics of the coating operation. Operational parameters such as line speed, bath configuration, and immersed hardware all contribute to the variability of the process. Numerical simulations of this process have determined the spatial distribution of temperature and composition of the critical constituents in the zinc bath in transient turbulent flow conditions. This simulation is able to identify the rate of formation and the location of the intermetallic dross particles (dross) within the bath. The generation of dross at the surface of the bath is also simulated experimentally using a mixing system with variable agitation and with air or nitrogen gas streams. Industrial tests carried out to continuously monitor the variation of the temperature and the Al and Fe composition are able to confirm the variations determined by the numerical simulations, validating the use of numerical simulation as an important means of analyzing a complex metallurgical process.

Effect of Initial Iron Content in a Zinc Bath on the Dissolution Rate of Iron During a Hot Dip Galvanizing Process

The mechanism of iron dissolution and the effect of initial Fe content in a Zn bath on the dissolution rate of iron were investigated using a finger rotating method (FRM). When the initial iron content, [Fe]°, in the zinc bath was less than the solubility limit, the iron content in the zinc bath showed a rapid increase, whereas a moderate increase was observed when [Fe]° was close to the solubility limit. Based on Eisenberg’s kinetic model, the mass transfer coefficient of iron in the present experimental condition was calculated to be kM = 1.2 × 10−5 m/s, which was similar to the results derived by Giorgi et al. under industrial practice conditions. A dissolution of iron occurred even when the initial iron content in the zinc bath was greater than the solubility limit, which was explained by the interfacial thermodynamics in conjunction with the morphology of the surface coating layer. By analyzing the diffraction patterns using TEM, the outermost dendritic-structured coating layer was confirmed as FeZn13 (ζ). In order to satisfy the local equilibrium based on the Gibbs–Thomson equation, iron in the dendrite-structured phase spontaneously dissolved into the zinc bath, resulting in the enrichment of iron in front of the dendrite tip. Through the diffusion boundary layer in front of the dendritic-structured layer, dissolved Fe atoms diffused out and reacted with Zn and small amounts of Al, resulting in the formation of dross particles such as FeZn10Alx (δ). It was experimentally confirmed that the smaller the difference between the initial iron content in the zinc bath and the iron solubility limit at a given temperature, the lower the number of formed dross particles.