Zinc Dross Research Articles

Study of Flow and Zinc Dross Removal in Hot-Dip Galvanizing with Combined Traveling Magnetic Field

The removal of zinc dross, which continuously generates and partially floats on a molten zinc surface, has been a persistent challenge during hot-dip galvanizing. Herein, a three-dimensional mathematical model coupled with the electromagnetic field, flow field and air-knife jet flow was established to investigate the flow and zinc dross removal in a zinc pot. Two types of traveling magnetic field combined modes (Mode 1 and Mode 2) were compared. The surface dross removal efficiency was introduced to evaluate the ability of the zinc flow field to compel the movement of zinc dross. The research findings indicate that, in comparison to the influence of strip steel line speed, both the electromagnetic field and air-knife jet have a more pronounced effect on altering the flow characteristics of a molten zinc at surface. The dross removal efficiency for Mode 1 is much far superior to that of Mode 2. With an increase in the driving current, the dross removal efficiency increases while the excessive driving current cannot promote the dross removal efficiency significantly.

An Experimental Study of Zinc Evaporation from Bottom Zinc Dross at Atmospheric Pressure and in Inert Atmosphere with Integrated CFD Modelling.

In the present study, the recycling process of bottom zinc dross was performed by evaporation and subsequent condensation at 800 °C for 30 min with an observed argon flow rate of 100-400 mL/min to ensure an inert atmosphere, to observe the evaporation rate and final form of the product. Under the set conditions of over 98% zinc purity, products in the form of nanofibres (thickness 500 nm), powder (size of spherical particles 2-5 μm), dendrites, and metallic forms were obtained. The employed mathematical modelling (via Ansys 2023R1 software) predicted the behaviour of the argon flow current in the quartz tube, as well as the temperature gradient in the quartz tube and in the close vicinity of the zinc sample. Via Inventor 2014 software, the rate of zinc sample heating was calculated. All the simulations were compared with the physical measurements and correlation was proven.

Recovery and utilization of zinc dross for sacrificial anode cathodic protection of steel structures

Zinc dross is highly zinc-rich industrial waste produced during galvanization of steel. It is a byproduct of the reaction between molten zinc and loose iron particles in a molten zinc bath. Generally, 10–20% of galvanized zinc is converted into zinc dross. This work proposes a unique way of recycling of dross into a high value sustainable resource material leading to development of sacrificial anode used in cathodic protection of steel. The electrochemical behavior was studied in 3.5 wt% NaCl solution. The anode performance test was performed as per the standard DNV-RP-B401 in an artificial seawater solution. The performance parameters, (closed circuit potential (CCP), anode efficiency, and consumption rate) of the recovered zinc anode from dross, are close to the commercial zinc anodes. It satisfies the required anode criteria. Hence, the recovered zinc anode from dross could be used as a sacrificial anode for the cathodic protection of steel structures.

Synthesis of Fe3O4/ZnO from Zinc Dross Waste as an Active Material for Dye-Sensitized Solar Cells

Abstract Zinc oxide (ZnO) is an attractive active material in emerging solar cell technologies, such as dye-sensitized solar cells (DSSCs), due to its high stability and electron mobility. The activity of ZnO can be enhanced by adding a small amount of impurity, such as iron oxide. Since zinc dross contains Zn as the primary element and Fe as the minor element, it can be used as a precursor to obtain iron oxide/ZnO. In this study, ZnO was prepared from zinc dross through a hydrometallurgy process and utilized as the active material for DSSCs. For comparison, pure ZnO was also prepared using zinc acetate as the precursor through the sol-gel process. X-ray diffraction (XRD) results show that pure ZnO was observed in the sample prepared using zinc acetate as the precursor, while ZnO with a Fe3O4 phase was observed in the sample prepared using zinc dross. Scanning electron microscopy (SEM) examinations reveal that the thickness of ZnO layer that was deposited onto fluorine-doped tin oxide glass was 11.3 ± 0.4 μm. The solar cell performance tests showed that the presence of dyes that adsorbed on ZnO synthesized from zinc dross could increase the efficiency of DSSCs up to 26.5 times while the ZnO synthesized from zinc acetate has 11.5 higher efficiency compared to the non-sensitized counterpart. Moreover, ZnO from zinc dross exhibited 1.2 times higher efficiency than ZnO from pure Zn precursor, indicating the feasibility of converting zinc dross waste into valuable materials.

Theoretical and Practical Evaluation of the Feasibility of Zinc Evaporation from the Bottom Zinc Dross as a Valuable Secondary Material

This study presents a theoretical and practical evaluation of zinc evaporation from bottom zinc dross (hard zinc) as a secondary zinc source (zinc content approximately 94-97%), which originates in the batch hot-dip galvanizing process. The thermodynamics of the zinc evaporation process were studied under the normal pressure (100 kPa) in the inert atmosphere, using argon with flow rate 90 mL/min. Samples were subjected to the evaporation process for 5, 10 and 20 min under the temperature of 700 °C and 800 °C, respectively. For the theoretical thermodynamic study, HSC Chemistry 6.1 software was used and final products, as well as residuals after the evaporation process, were analyzed by SEM (Scanning Electron Microscopy) and EDX (Energy Dispersive X-ray). Calculated and experimental argon consumption in the process of zinc evaporation has been compared. A high purity zinc with efficiency over 99% was reached. Due to a dynamic regime, argon consumption at the temperature of 700 °C and 800 °C were 7 times and 3 times, respectively, less than calculated.

Numerical Simulation of the Electromagnetic Dross Removal Technology Applied in Zinc Pot of Hot-Dip Galvanizing Line

The forming of zinc dross floating on the surface of molten zinc in zinc pot is inevitable during hot-dip galvanizing production. The cleaning of zinc dross has always been a challenge and a difficult problem to solve. Based on the electromagnetic field theory and its application, a new electromagnetic dross removal technology was proposed, and the zinc dross driven by flowing molten zinc was possible to remove in an electromagnetic field circumstance. Through the coupling simulation of electromagnetic field and flow field, the electromagnetic force acting on molten zinc and the flow situation of molten zinc were simulated. The results showed that electromagnetic field can effectively act on the top surface of molten zinc and affect the flow of molten zinc. Different load conditions of electromagnetic field and the distance between the bottom surface of the iron core and the top surface of molten zinc related to zinc dross removal effect were discussed. Finally, the optimal application parameters of the electromagnetic dross removal technology were put forward.

Separating Silver from Tin Silver Alloy Residue: Effect of Agitation Rate

In this paper, research on the effects of agitation rate for desilvering tin silver alloy residue by using pyrometallurgy was carried out. SnAg alloy residue with 92 wt.% tin and 3.56 wt.% silver was used in this study, and 99.999 wt.% zinc was added as metal solvent. Residues were melted to a temperature of 400 °C for enriching tin silver alloy. The obtained tin silver alloy was melted in a temperature range of 450 °C to 500 °C by adding zinc to evaluate zinc dissolution. The obtained tin silver zinc was agitated at different agitation rates for 20 min at a temperature of 480 °C, then cooled down while stirring to an eutectic point of tin zinc alloy (198.9 °C) to remove silver zinc dross. X-ray Fluorescent-1800 (XRF-1800) and Field Emission Scanning Electron Microscopy Energy Dispersive Spectroscopy (FE-SEM-EDS) analyses were performed in this research. Different factors including holding time, zinc dissolution, agitation time and agitation rate were evaluated. The results revealed that an agitation rate of 600 RPM, 25% Zn and 60 min at a temperature of 198.9 °C were efficient. Zinc silver was removed as dross every 20 min to get 92% silver separation efficiency, and the use of supergravity centrifuge is highly recommended to get best separation efficiency.

Zinc powder preparation from zinc dross

Direct electro winning of zinc containing waste under anodic material may be useful in electrowinning of zinc powder. The present invention deals with the electrolytic zinc powder preparation from zinc dross in sodium zincate solution. The zinc dross was first expose to SEM-XRD for micrographic study and then subjected for wet chemical analysis. It was observed that most of the zinc is in metallic state with few amount of zinc is associated with iron. Different parameters such as current density, current efficiency, voltage and concentration of electrolyte have been studied to establish the process. It was observed that at 5 amp/dm2 current density the formation of zinc powder is possible with 1.23 kWh per kg of energy consumption. The corresponding impressed voltage was found 1.2 V and with a current efficiency of 90 %.

Recovery of zinc as zinc phosphate and by-products from hydrometallurgical treatment of hot-dip galvanizing (Zn-Al) dross

Zinc dross is the waste product generated during the hot-dip galvanizing, wherein around 11% of the total zinc is arrested by the dross leading to huge zinc losses. Though, there exist several pyro-metallurgical approaches to recover zinc but these are highly energy and cost intensive process; where hydrometallurgical processes take an edge. In this regard, this study holistically focusses on the hydrometallurgical recovery of zinc as zinc phosphate and other impurities like Al as alumina from zinc dross (Zn-Al) obtained from in-house hot-dip galvanizing unit at our laboratory. Zinc dross is leached as received in aqueous sulphuric acid medium without pulverization and stirring requirements, followed by separation of aluminium using NaOH based precipitation. Aluminium hydroxide precipitate is calcined to obtain alumina, whereas the supernatant solution is subsequently treated with disodium hydrogen phosphate to obtain products like zinc phosphate and sodium sulphate. The proposed process is simple, facile and scalable for recovery of zinc and other valuables from dross.

The utilization of carbonized coffee in purifying zinc dross waste by pyrometallurgy method

The purification of zinc oxide has been carried out from zinc dross waste by pyrometallurgy method. The amount of zinc dross waste was cleansed by using aqua DM liquid with ratio of 1:10, then this amount was characterized using XRF to determine chemical compounds contained within the 90% of zinc dross waste, while impurity compositions of Fe, Al, and Mg were found. Hence, the amount of zinc dross waste was mixed to carbonized coffee within two ratios, i.e. 87.5%wt: 12.5%wt, and 75%wt: 25%wt. Carbonized coffee is obtained from carbonization of coffee grounds waste from the coffee industry. The mixture samples were then dissolved by aqua DM, followed by milling treatment by performing Planetary Bill Mill for 40 min, so that the muddy-phase were obtained. This sample was then filtered and it was heated inside an oven at 100 °C for 24 h to powder. The mixture powder of zinc dross and carbon was then placed in pyrolysis vessel at 1200 °C for 2.5 h. The obtained amount of zinc oxide powder was characterized by using XRF, and this has 98% of purity with impurities element i.e. Al2O3, Fe2O3, MgO, and SiO2. Thermal testing was performed for ZnO sample by using DT instrument to investigate the effect heating to the reaction events. The analysis of DTA showed that the mixture sample of zinc dross and carbon had reaction sequences at 800 °C. The morphological analysis conducted by SEM and OM depicted that ZnO has agglomeration characteristics with uniformity shape among particles. The size of the particles is between 1900 μm and 9378 μm.

The pyrometallurgical recovery of zinc from electric arc furnace dust (EAFD) with active carbon

The reduction of minor impurities (e.g., Ferrite, Magnesium, Lead, Chromium) from Zinc rich-EAFD with active carbon addition was investigated at temperature between 900-1300 °C. The result was powder with higher zinc content which then analysed by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD) and scanning electron microscope (SEM) equipped with X-Ray energy dispersive spectrometry (EDS). The thermogravimetry (TG) and differential thermal analysis (DTA) of EAFD and carbon mixture was conducted previously to grasp the temperature of thermic reaction of mixture. Recovery of 90wt% zinc from EAFD available was achieved up to 99.2wt% after the pyrometallurgy process at temperature 900 °C in atmosphere pressure while the extension of the time corresponds to the amount of recovered zinc dross.

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.

Recovery of Zinc From Zinc Dross Using Pyrometallurgical and Electrochemical Methods

Recovery of zinc from its dross was investigated using electrochemical and pyrometallurgical methods. Almost 100% pure zinc was obtained using these methods. A small bench scale system for the investigating the recovery of zinc using pyrometallurgical methods was developed. The system based on the evaporation of zinc (in the dross) at 1050oC and condensing zinc vapors into pure zinc in a separate crucible. Almost pure Zn (99.95%) is obtained using this method. Recovery of zinc was also performed using electrowinning from acidified zinc sulfate bath and electrorefining of zinc dross anodes in alkaline ammonia bath. In either method different parameters including current density and deposition time were addressed. Zinc powder of almost 100% purity was obtained.

Influence of Steel Strip Temperature in Formation Zinc Dross During Process Production Using Continuous Galvanizing Line (CGL) Machine

To control the occurrence of zinc dross during galvanizing process using production Continuous Galvanizing Line (CGL) machine, it is necessary to control steel strip temperature before entry into zinc bath. The Steel strip temperature controls were variable at 320°C and 400°C and zinc bath temperature was fix at temperature 460°C. At temperature steel strips of 320°C, zinc bath was checked using spectrometry, the results of Fe content 0.1293% and Al 0.0759%, because the solubility of Al is lower than Fe, the dross occurs become bottom dross. If the zinc dross change become bottom dross, the bottom dross could decrease quality of product and life time of zinc pot, because bottom dross settled at the floor. Bottom dross properties very hard and absorb heating, then at that position bottom dross make hot spot in the floor, finally zinc pot leakage. At temperature steel strip 400°C, the results content of Al 0.1667% and Fe 0.1217%, due to high temperature steel strip make solubility of Al become higher than Fe, therefore float at the zinc bath become top dross.

Zinc stearate from galvanizing waste materials and its use as thermal stabilizer in PVC industries

Galvanizing industries of Bangladesh produce profuse amount of environmentally hazardous solid waste materials like zinc dross which contains significant amount of valuable zinc and harmful heavy lead. Zinc was extracted as zinc chloride (ZnCl2) from zinc dross. Zinc stearate (ZnSt2) samples were prepared by precipitation method from stearic acid, sodium hydroxide and ZnCl2 by varying the amount of the reagents and product yield found within the range 96.06-99.18%. Characteristic peaks of ZnSt2 were investigated by Fourier Transform Infrared Spectroscopy (FTIR). Differential Scanning Calorimeter (DSC) onset curve assigned accurate melting point within the range 122.84-124.03°C. Surface morphology of ZnSt2 was observed by Scanning Electron Microscope (SEM) and products had semi-crystalline structure. Thermal stability of ZnSt2 was evaluated by Thermo-gravimetric Analyzer (TGA) that complied with literature. A combination of ZnSt2 and Calcium stearate (CaSt2) at 1:1 ratio was used as thermal stabilizer in the powder commercial grade PVC resin and performed better thermal stability. The dehydrochlorination temperature of PVC with mixed stearates was 344.67±1.04°C for 10% (w/w) loading whereas for PVC, PVC with 10% (w/w) ZnSt2 and PVC with 10% (w/w) CaSt2, it was 269.83±1.04°C, 317.33±1.26°C and 323.33±2.08°C respectively.Bangladesh J. Sci. Ind. Res. 51(4), 261-270, 2016

Apply TRIZ to Improve the Molten Zinc Corrosion Tester in Steel Manufacturing

Abstract In order to study the mechanism of molten zinc corrosion on specific materials, a molten zinc corrosion tester was developed to simulate the working condition in a zinc pot. However, the tester may cause severe oxidation of zinc, which becomes dross floating on the surface. Once the dross accumulated to a certain level, the molten zinc became viscous and affected the movement of the samples. Based on the Teoriya Resheniya Izobretatelskikh Zadatch (TRIZ) methodology and heuristic technique, this study improved the design of the tester so as to solve the oxidation problem. The objective of this study is to minimize the formation of zinc dross to be less than 2 kg in 2 days. After several attempts, the tester reduced oxidation of molten zinc successfully from 2.6 kg of zinc oxide every day down to 2.52 kg every three days. The improvement is 68 %, which is a very outstanding achievement.

Dechlorination of zinc dross by microwave roasting

Traditional treatments of zinc dross have many disadvantages, such as complicated recovering process and serious environmental pollution. In this work, a new process of chlorine removal from zinc dross by microwave was proposed for solving problem of recycling the zinc dross. With better ability of absorbing the microwave than zinc oxide, the main material in zinc dross, chlorides, can be heated and evaporated rapidly during microwave roasting. Various parameters including roasting temperature, duration time and stirring speed were optimized. The microstructure of roasted materials was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). The content of the chloride was analyzed by the method of chlorine ion selective electrode. The experiments indicate that the best duration time is 60 min with a stirring speed of 15 r/min during the microwave roasting process. The dechlorination rate reaches peak value of 88% at 700 °C. The chlorine is removed as HCl gas when water vapor is used as activating agent, which means that it can be recovered into hydrochloride acid.

Influence of Rare Earth on Hot-Dipped 55%Al-Zn Alloy Coating

Simulation experiment was done to investigate the effects of rare earth on hot-dipped Zn-55%Al alloy coating. The results show that the rare earth has little effect on the zinc dross and its burning loss is about 10%. The microstructure of coating is similar to that of solidification bath, and which is made up of phases of rich aluminum, rich zinc, rich silicon and rare earth, and intermetallic layer of Al-Zn-Fe-Si. The rare earth phase is needle or rod, and mainly distributed inside rich zinc phase and on the interface between the coating and steel substrate. The rare earth has no obvious influence on coating grain and spangle size. The appropriate addition of rare earth would be helpful to improve the coating bending formability and corrosion resistance.

Improving the Sink Roll life in Galvalume

Galvalume is a Continuous Galvanizing Line. JSW Ispat Steel Ltd. Kalmeshwar has to frequently replace the sink roll assembly used in Zn-Al tank of the Galvalume. The mean time between replacements is very less as compared to expected mean time between failures (expected MTBF). This is due to deposition of zinc dross on the surface of roller. This result in uneven or improper Zn-Al coating on sheet surface. To avoid this sink roll has to replaced. The frequent replacement of roller assembly results in Stoppage of production, material loss, start-up loss and increased cost of production. This paper proposes an alternative material to extend the life of sink roll. Galvalume is a continuous hot dipping process in which steel sheet is dipped in Zn-Al pot. Zinc pot contains Aluminum (55%), Zinc (43.5%) and Silicon (1.5%). The hot dipping is carried out at 6050 c. The chemical reaction between molten ZnAl alloy with iron at 6050c results in the formation of complex compound “dross”. This dross deposits on sink roll surface. It causes: 1. Uneven deposition of dross on sink roll. 2. Impressions on sheet and variations in coating on sheet. 3. Sheet showing dross Build-up. Due to this quality of sheet is lowered and sheet is downgraded. This downgrading brings financial loss to the company. To avoid this, frequency of roller replacement is increased. However this has following disadvantages: 1. Increased loss of production due to frequent stoppages (During removal and refitting of assembly). 2. Zinc loss due to frequent change of roller assembly. 3. Additional cost of re-machining of sink roll. 4. Increase idle time in the process. The project is aimed at increasing the life of sink roll or extending the time period between the sink roll replacements. The increased time between replacements will help in overcoming the above disadvantages. Sink Roll TheSink roll, is a roll used in molten zinc tank in continuous galvanizing line. It is generally made of SS316L Ferrite free, stainless steel that can withstand extreme temperatures & high corrosion for extended periods of time. It made by centrifugal casting.[11] There body uses different shapes like straight body, crowned and tapered depending upon applications. A variety of groove patterns and pitches are made on the surface as per as customers specifications. Special grooves are provided for carbide coatings. [8] Sink roll or Pot roll immersed in the molten zinc bath is affected by the dross is also attacked by the molten zinc leading to pitting and build ups. All these factors affect the coil surface. Such rolls have very short life. Sink rolls are works in a very corrosive environment, i.e. molten zinc. They typically see temperatures in excess of 6000C for weeks at a time. Materials used are made to withstand this criteria, so they are also difficult to machine.[16] The roll is made of SS316L material. It is a ferrite free stainless steel grade having surface hardness RC 10. The body is a centrifugal cast stainless steel and the end ball/journal is from a static casting. Most of these rolls have no coatings on them. An uncoated roll may last up to 2 weeks, but with carbide coatings and special bushings they laste up to 5 weeks. However for Galvalume the life is reduced drastically due to dross formation (pick-up) and high tempurature ( i.e above 6000 c ). An apparatus called ‘Scrapper’ is installed in a molten metal plating line includes a blade pressed against a roll dipped in a

Analysis Of Waste Production Management And Environmental Conditions On Coating Process Performancebefore And After The Implementation Of Environmental Management System (EMS)

The phenomenon of proactive environmental management began in the 1990's where manufacturing industries were aware the importance of corporate sustainability through sustainable environmental management. Various strategies can be done in a proactive environmental management. This study emphasized the development of conditions environmental performance companies in minimizing waste, especially in production process that contains a lot of waste. The company has trying to implement a standardized EMS, through its own sludge wastewater treatment as a raw material for making bricks, while for solid waste (zinc dross and zinc ash), had been sold to external parties from the beginning. There isn’t recycling process, Galva furnace repair and improvement work on the system setting WWT or the WWTP. EMS implementation is strengthened through the acceptance of ISO 14000 in 2007. The condition of Company's environmental performance related to waste minimization in the galvanizing process before and after implementing EMS was measured using input indicators (material), the input of water and energy use, and output of products in the form of waste (solid or sludge). The result did not correspond quantitatively with the indicators used in ISO 14000. Based on the quantitative result , a company processing waste , did not change significantly.