Zinc Dross Research Articles

Synthesis and Characterization of Zinc Oxide Tetrapods from Zinc Galvanization Dross

As an interesting material in large field area, ZnO synthesize has been widely observed. In this research, synthesize was carried out using zinc dross, waste from galvanization process, as starting material by simple heat treatment method. The as-synthesized ZnO obtained were further underwent post-anneal and post-hydrothermal treatment series. From the characterization data, it was found that highest crystallite size was obtained in sample treated with post-hydrothermal treatment at 150oC for 12 hours with value of 1371 nm, which corresponds to its lowest Eg value of 3,086 eV.

A Small Amount of Alloying Additions Applied in Hot Dip Galvanizing

Investigating the changing quality of galvanized parts when pure zinc plated with other alloying additions. In the procedure of hot dip galvanizing, when pure zinc plated without other alloying additions, the corrosion resistance of zinc coating is poor, meanwhile the bath surface will produce a number of zinc dross, zinc ash, and this phenomenon will cause a waste of zinc, resulting in an increase in product costs, and the surface of product is relatively dark, the brightness is not enough, whilst sometimes even form a phenomenon of the formation of the Pan-color on the surface of the galvanized parts. However, when a proportion of aluminum or rare earth elements is added into melting zinc, the corrosion resistance of coating will be improved and much better than pure zinc galvanized parts;as the decrease of zinc ash, the cost will be reduced;synchronously the limititation of superficial quality above-mentioned will be improved. Via evaluating the superficial quality of galvanized parts and the corrosion resistance, the whole performance will be significantly improved when 0.5% aluminum and 1.5% rare earth elements is added into melting zinc.

Separation behaviour of zinc dross from hot dip galvanising melts of different aluminium concentrations by alternating magnetic field

Dross in zinc pots is the most important factor that impairs the surface quality of hot dip galvanising automobile steel sheet. Separation behaviour of zinc dross from galvanising melts of different Al concentrations (0·12, 4·5 and 55·0 wt-% by an alternating magnetic field has been investigated in order to reduce the dross defects on steel sheets. The properties of different zinc drosses were investigated by means of EDAX and the quantitative metallographic method and the conductivities were measured by physics property measurements system. The experimental results show that the zinc dross in different hot dip galvanising melts has different morphologies, compositions and structures, and the average particle size of the dross increases with the Al concentration. In the case of extra iron (above the solubility limit) in the zinc melt, zinc dross quantity also increases with the Al concentration. All of the three types of zinc dross particles >5 μm can be successfully separated when the magnetic frequency is 17·5 kHz, effective magnetic flux intensity is 0·05 T, imposed time is 15 s and the cross-section of the ceramic square pipe is 5 × 5 mm.

Identification of Fe–Al–Zn dross phase in galvanised zinc bath and its separation by method of alternating magnetic field

In this study, the separation of Fe–Al–Zn dross phase from hot dip galvanised zinc bath was conducted by using alternating magnetic field. The compositions of the zinc dross were detected by energy dispersive spectrum. The electrical conductivities were measured by physical properties measurement system. The separation efficiency of the zinc dross in different channels was examined by the quantitative metallographic method. Experimental results show that the zinc dross particles with diameter larger than 5 μm can be separated successfully when the processing parameters can selected appropriately.

Continuous separation of Fe–Al–Zn dross phase from hot dip galvanised melt using alternating magnetic field

Experiments to continuously separate Fe–Al–Zn dross phase from hot dip galvanising zinc melt were conducted on a laboratory scale apparatus by using high frequency alternating magnetic field. Effects of processing time (t) on separation efficiency were investigated. The experimental results show that using the electromagnetic repulsive force resulting from the electrical conductivity difference between zinc melt and Fe–Al–Zn dross phase, the deleterious zinc dross particles causing surface defects of galvanising steel sheets can be continuously separated from the zinc bath under alternating magnetic field, and the separation efficiency increases with the increase in processing time. When the magnetic frequency is 17·5 kHz, the effective magnetic flux intensity is 0·1 T, the cross-section of the ceramic square pipe is 10 × 10 mm, and the processing time is 0·6–2·5 s, the separation efficiency of zinc dross varies from 43·76 to 85·71%, and the experimental results are in reasonable agreement with the theoretical results.

Electrorefining zinc dross in ammoniacal ammonium chloride system

A zinc dross was cast into anodes and electrorefined in an ammoniacal ammonium chloride electrolyte (NH 3–NH 4Cl) to produce high purity zinc. The influence of several factors, such as zinc concentration, current density and temperature, on cathodic current efficiency and power consumption were investigated. The results indicated that increasing Zn concentration increased the current efficiency, but, very high Zn concentrations affected the progress of the electrolysis of zinc dross. The power consumption can be decreased effectively by increasing the temperature of electrolyte. High current density adversely affected the quality of the cathodes and increased the power consumption. The morphology of cathodic zinc can be improved by increasing Zn concentration at an appropriate current density and its purity was very acceptable. All the experimental results obtained showed a technical feasibility of the NH 3–NH 4Cl system as an electrolyte system for electrorefining of zinc dross.

Hydrodynamic study of a toroidal fluidized bed reactor

Hydrodynamic behavior of a newly developed toroidal fluidized bed reactor is studied in this work. The reactor has a gas distributor consisting of angled blades in an annular ring at the reactor bottom. The driving force for particles to move over the distributing blades comes from the velocity head of gas jets accelerated upon entering the blade spacing. Relevant hydrodynamic behaviors are measured with various inert materials in a pilot scale 400-mm toroidal fluidized bed reactor. The observed hydrodynamic behavior is found to be essentially predictable at ambient temperature by conventional hydrodynamic models. Fine particle tracking on the reactor wall is clearly observed through oxidation of zinc dross at a bed temperature of around 1120°C, and is simulated on the basis of a simplified mathematical model. Hydrodynamic issues, such as particle flying trajectory and retention time in the reactor, are discussed based on the developed model.

Dechlorination of a zinc dross

The possibility of decreasing chlorine content of a zinc dross containing 1.40% chlorine by washing with distilled water and sodium carbonate was investigated in this study. The dross sample was obtained from ÇINKUR which is the only primary zinc producer in Turkey. Temperature, time and solid–liquid ratio were the investigated variables in distilled water washing experiments. In addition to these variables, the effect of sodium carbonate amount was also studied in sodium carbonate washing experiments. The results showed that there was no advantage of using sodium carbonate in chlorine removal. Washing the zinc dross simply with distilled water at 95°C for a short period of time such as half an hour and at a suitable solid–liquid ratio between 1:2–1:10 removed about 80% chlorine found in the dross. Chlorine content decreased from 1.40% to about 0.20–0.30% in the dross.

Recovery of zinc and some of its valuable salts from secondary resources and wastes

In Egypt, several kinds of recurring zinc-containing waste materials are available for metal zinc recovery. These include zinc scrap from spent dry cell batteries, zinc dross and zinc ash. These secondary resources were analyzed and their zinc contents determined. Pyrometallurgical and hydrometallurgical recovery processes for zinc and its salts were carried out. The factors affecting the performance and efficiency of the processes; such as particle size, temperature, concentration of acid leaching and time were studied. The results obtained revealed that zinc metal is successfully recovered from these secondary resources. The recovery efficiency amounts to 89% and 63% for zinc waste materials having a particle size diameter of + 1.25 mm and (− 0.4 + 0.315 mm), respectively. An optimum percentage of 10% weight of ammonium chloride fluxing agent was obtained. The optimum temperature for the recovery process was 600°C. With respect to the fine fraction of zinc dross, zinc ash and the slag left after pyrometallurgical treatment, acid leaching for extraction of the metal salts yields salts with a high efficiency (99%). The cost of recovery is acceptable on the basis of the low price of the materials input and energy consumption. Results were explained by an oxidation model and a salt refining mechanism.

秋田製錬所における含銅亜鉛ドロスの処理

秋田製錬所における含銅亜鉛ドロスの処理

溶融Znめっきドロスと少量のAlの溶融混合体におけるFe-Al合金晶の形成反応

Zinc dross specimens containing 3 mass%Fe were heated with various amounts of Al-50 mass%Zn alloy at 773 to 1023 K, in order to investigate the formation process of Fe-Al alloy crystals in the Al addition method employed for Zn recovery from the dross formed at the bottom of a hot-dip galvanizing bath.In the dross specimens heated with the amounts of the Al-Zn alloy equal to 1-3, 3.6-6 and 8-12% of their weight, crystals of α phase, α and Fe2Al5 phases and Fe2Al5 phase are formed, respectively. Although crystals of δ1(FeZn7) and ζ(FeZn13) phases are also formed together with these crystals, they decrease gradually with the lapse of heating time and disappear completely when the specimens are heated with the amount of the Al-Zn alloy more than 4.4% of their weight. The decrease in the amounts of δ1 and ζ crystals is due to the decrease in Fe concentration in molten Zn by crystallization of the α and Fe2Al5 phases and their disappearance time decreases with increase in heating temperature and amount of Al-Zn alloy.The maximum value of area fraction and minimum Al content of the Zn matrix (η phase) are obtained by heating with the amount of Al-Zn alloy equal to about 5% of the weight of the zinc dross specimen. The optimum amount of Al in the Al addition method seems to be about 0.8 times the Fe content in the dross, although the amount has been regarded as 1.5 times.

Investigation of use of zinc dross as a substitute for zinc dust in solution purification in zinc electrowinning hydrometallurgical plant

Zinc dross generated during the melting of zinc cathodes contains appreciable amounts of metallic zinc contaminated with high levels of chlorides, which prevents its direct use in solution purification at hydrometallurgical electrowinning zinc plants. An investigation has been made to separate the available metallic zinc by dechlorination and leaching. Laboratory-scale experiments with available dechlorination processes, use of the metallic zinc thus produced in the solution purification and zinc recovery from the leach solution are reported here, with results of plant-scale trials. The method reported provides an almost chloride-free zinc sulphate solution and a high grade of metallic zinc which performs the same function as that of fresh atomised zinc dust for the removal of cadmium and copper in the relevant purification stages in zinc and cadmium circuits, at a much lower cost.

Recovery of zinc from melting furnace residue

Slag from a zinc cathode melting furnace contains about 60% metallic zinc. This may be increased to 80–90% in the coarse size fractions (+200 mesh) by grinding and sieving. Residual zinc oxide may be removed by leaching with 5% H 2SO 4. Zinc recovery is about 77–84%. The zinc from the coarse size fractions may be melted for ingot production, whilst the finer material is suitable for cadmium cementation (−200 mesh material is similar to zinc dross). The process has been studied on both the laboratory and plant scales and process engineering indicates that it is economic.

Characteristics of electrolytic zinc powder produced from zinc dross

The technology of electrodeposition of zinc metal powder from zinc dross is reviewed. Electrolysis was carried out utilizing sodium zincate solution obtained by dissolving the zinc dross in caustic soda and separating the undissolved from residue. The effect of both the cathode current density and the zinc ion concentration on the shape, structure, size, particle size distribution and specific surface area of the produced powder was investigated.