Electrolytic Zinc Plant Research Articles

Efficient Corrosion/Erosion-Resistant Linings for Rotary Kilns

We studied the service conditions for the lining of the Waelz kilns at the Chelyabinsk Electrolytic Zinc Plant and the Ust’ Kamenogorsk Lead and Zinc Plant, and identified the primary sources of wear on the refractories. Refractory wear inWaelz kilns primarily occurs via a chemical reaction between the refractories and the components of the charge, which is then followed by abrasive wear. PKhPP [periclase-chromite fused grains] and KhPT [chromite-periclase thermal shock resistant] refractories were found to be the most stable under the service conditions in Waelz-kiln linings. The refractories were impregnated with coal-tar asphalt for improved durability. A test batch was produced and tested in the lining of a Waelz kiln. High temperature glue — for Waelz-furnace linings at various non-ferrous metallurgical plants — and mortar — for ceramic joints with better physical and chemical properties throughout the entire lining — were developed. The shape, optimum dimensions, and design of the ceramic products, and brickwork designs based on these products were all studied. The brickwork designs were tested inWaelz kilns at several ferrous and non-ferrous metallurgical plants.

Reductive leaching of zinc and indium from industrial zinc ferrite particulates in sulphuric acid media

Zinc ferrite is the principal constituent in zinc neutral-leach residue (NLR) which is commonly treated by hot-acid leaching in electrolytic zinc plants. Reductive leaching of zinc ferrite with sphalerite concentrate as a reducing agent was performed. It was found that leaching of zinc ferrite in the presence of sphalerit concentrate was a viable process that effectively extracted zinc and indium and converted Fe3+ into Fe2+ at the same time. Reflux leaching tests by two stages were performed to achieve extractions of 98.1% for zinc and 97.5% for indium, and a Fe2+/Fe3+ molar ratio of 9.6 in leach solution was also obtained. The leaching behaviors of other elements, such as iron, copper and tin were also studied. The results showed that iron and copper were completely leached, whereas tin presented lower extraction values.

Corrosion-Erosion-Resistant Carbon-Containing Refractories for Nonferrous Metallurgy Units

Results are provided for development of optimum technology for preparing periclase-carbon refractory (PCR) by introducing carbon and antioxidizing agents into periclase refractory in different ways, i.e., pressing or vacuum impregnation with coal tar paste. Lining zones are determined within which use of PCR is rational. PCR refractories are tested and introduced into the slag belt of a reverberatory furnace in the Krasnoural Copper Smelting Combine, and KhPT refractory impregnated with carbon paste is introduced into the lining of Chelyabinsk Electrolytic Zinc Plant and Ust’-Kamenogorsk Lead-Zinc Combine Waelz kilns. Use of this lining increased a unit campaign by 40 – 45%.

The recovery of metallic cadmium from the cadmium containing residue in a electrolytic zinc plant

This report presents a process for recovery and purification of metallic cadmium from a residue of the purification process for zinc sulphate solution in Thai Nguyen electrolytic zinc plant. The cadmium containing residue was digested by sulfuric acid of 140 g/l at a temperature of 700C for 4h, the obtained solution will be purified for removal of some impurities such as iron, copper, etc. The purified solution with concentration 50 g/l of Cd, 120 g/l of sulphuric acid and 0.1 g/l of gelatin as an additive will be subjected to an electrolysis process with current density of 50 A/m2 for recovery of metallic cadmium. The temperature of electrolyte is lower 400C. Overall recovery of cadmium is 90%, purity of the obtained metalic cadmium is up to 99.0%.

Effective Highly Resistant Waelz Kiln Linings

Conditions are analyzed for service of Waelz kiln linings of the Chelyabinsk Electrolytic Zinc Plant and the Ust’-Kamenogorsk Lead and Zinc Combine, and the main reasons for refractory wear are revealed. Refractory grades PKhPP and KhPT are most resistant for service conditions in Waelz kiln linings. In order to improve Waelz kiln lining life chromite-periclase heat-resistant refractory lining schemes are developed and introduced, a high-temperature adhesive is developed, impregnation of refractories with coal-tar pitch is accomplished, and a test batch of objects is prepared and tested in a Waelz kiln lining. A laying mortar based on self-propagating high-temperature synthesis is developed. Spatial geometric shapes, optimum dimensions, ceramic object structure, and layups based on them are studied. Linings are tested in theWaelz kilns of a number of enterprises.

Determination of the optimum conditions for the leaching of Cd–Ni residues from electrolytic zinc plant using statistical design of experiments

This research is part of a continuing effort to reduce environmental conflicts and occupational hazards of cadmium bearing zinc plant residues (ZPR's) and to break through this problem and recover valuable constituents of the wastes. In this paper, effects of influential factors on extraction efficiencies of Cd, Zn, Ni, Pb and Cu from Cd–Ni filtercake as a major ZPR were investigated. In the view of above, the systematical and analytical evaluation method of Taguchi quality engineering has been applied for the leaching of the Cd–Ni filtercake to evaluate the optimal experimental conditions and hence to achieve the highest leaching performance and the best robustness of quantitation from the least number of trials in a batch laboratory scale. An L 25 orthogonal array (OA, five factors in five levels) was employed to evaluate the effects of temperature ( T = 25, 35, 45, 55 and 65 °C), acid concentration ( C = 0.31, 0.51, 0.82, 1.22 and 1.84 M), time ( t = 15, 30, 45, 60 and 90 min), pulp density (S/L = 125, 142.86, 166.67, 200 and 250 g/l) and stirring speed ( R = 200, 300, 400, 500 and 800 rpm) on extraction percent of the individual metals. Statistical analysis, ANOVA, was also employed to determine the relationship between experimental conditions and yield levels. The results showed that increasing temperature reduced performance characteristics. Two approaches were taken into consideration for the experiments, i.e., selective and collective leaching, and then the optimum conditions were sought for each considered approach. The experimental results for selective leaching showed that under optimal leaching conditions ( T: 45 °C, C: 0.82 M, t: 60 min, (S/L): 250 g/l, R: 400 rpm), the extraction of cadmium, zinc, nickel, lead and copper were 90.29, 96.86, 8.66, 0.11 and 0.01, respectively. However, the same results for optimal collective leaching conditions ( T: 25 °C, C: 1.22 M, t: 60 min, (S/L): 142.86 g/l, R: 200 rpm) showed that the extraction of Cd, Zn and Ni could be over 95%, with negligible dissolution of lead and copper.

Water leaching and magnetic separation for decreasing the chloride level and upgrading the zinc content of EAF steelmaking baghouse dusts

Recycling scrap iron and steel in electric arc furnaces (EAFs) generates very fine metal-containing dusts which can present major environmental problems. This paper describes experimental work on a relatively novel, simple, and inexpensive process for decreasing the chloride content and upgrading the zinc level of dust from an Australian plant, to produce saleable products and environmentally safe waste products for disposal. The dust contained about 2.1% Cl as various chlorides, 23.1% Zn as zincite and franklinite, 27.1% Fe as magnetite, franklinite, and hematite, plus small quantities of lead, cadmium, chromium, and other materials. The dust was very fine ( P 80 about 2 μm). Individual particles were commonly aggregates of fine spheres and other shapes. Simple water washing at ambient temperatures and natural pH (12) for 60 min extracted 99% of the chlorides, giving a residue assaying 200 ppm Cl. This residue was strongly coagulated by lime present in the dust and settled rapidly. The wash solution contained low levels of iron, zinc, lead, cadmium, and chromium, most of which could be removed by sulphide precipitation. Wet magnetic separation with a Davis tube was investigated. At the lowest field strength employed (0.6 A), 95% of the zinc was recovered in a non-magnetic product assaying 28% Zn and 24% Fe. At the highest field strength (1.6 A), 91% of the zinc was recovered in a non-magnetic product assaying 29% Zn and 25% Fe. Wet cycloning at a nominal separation size of 2–5 μm gave a cyclone overflow product assaying 31% Zn and 26% Fe, and containing 85% of the zinc. All these results fit a typical zinc grade–recovery relationship. The proposed process of water washing followed by magnetic separation or cycloning would produce a relatively high-zinc, low-iron, low-chloride product suitable for treatment in a lead–zinc smelter or electrolytic zinc plant, a high-iron, low-zinc product suitable for land fill, and a treated waste water for discharge to a sewer.

Development of Processes for Environmental Protection Based on Self‐Propagating Reactions

AbstractFor Abstract see ChemInform Abstract in Full Text.

On the use of industrial scraps for the treatment of zinc hydrometallurgical wastes by self-propagating reactions

In this work the development of a technique is presented that consists of blending highly toxic solid waste from electrolytic zinc plants, i.e. paragoethite waste, with suitable amounts of aluminum, silicon, and ferric oxide, and igniting the resulting mixture so that a self-propagating front reaction rapidly travels through the mixture without requiring additional energy. Specifically, the possibility of substituting commercial additives, needed for guaranteeing the self-propagation of the reacting mixture, with industrial scraps is demonstrated. In fact, commercial ferric oxide can be replaced by steelmaking scraps containing about 85% of iron oxides, while electronic industry by-products, characterized by Si content equal or higher than 94 wt.%, can be used instead of the corresponding commercial reactant. Similarly to the results obtained when commercial additives were used, the main reaction product, representing 70–80 wt.% of the total mass of the original mixture and obtained when the paragoethite waste content in the starting mixture does not exceed 30 wt.%, is constituted by an alumino-silicate matrix which embodies heavy metals, such as Pb, Zn, and Cd. Leaching tests of this solid product demonstrate the fulfillment of the environmental regulations for heavy metals.

Opposing scaling and fouling during electrodialysis of sodium fluoride solution in a membrane cell reactor

Electrodialysis of a sodium fluoride solution in a membrane cell reactor was studied as part of a process to bleed magnesium from process liquors of electrolytic zinc plants. Because, in industrial practice, the long-term stability of membranes is a must, performance of the membranes over a long time was studied. Scaling of one of the membranes occurred as a result of the specific composition requirements. Without opposing measures, this scaling causes the reactor voltage to increase continuously. Four effective measures could be identified to reduce the scaling. Creating a small pressure difference over the membrane, causing the membrane to bulge and the scaling to breakdown, was very effective as well as the addition of dilute acid pulses. Furthermore, creating a turbulent environment and brushing the membranes could be applied to reduce the scaling. One of the membranes also experienced fouling, although this fouling did not influence the selectivity of the membrane for at least 500 h.

Development of processes for environmental protection based on self-propagating reactions

The possibility of exploiting self-propagating reactions for environmental protection is discussed in this paper. In particular, results obtained at the laboratory scale and related to the fixation and consolidation of high level radioactive wastes, the recycling of silicon sludge and aluminum dross produced by semiconductor industries and aluminum foundries, the treating and recycling of a highly toxic solid waste from electrolytic zinc plants, and the degradation of chlorinated aromatics, are examined with particular emphasis on the latter case. Specifically, the self-propagating destruction of hexachlorobenzene and 2-(2-4-dichlorophenoxy)-propanoic acid with calcium hydride as reductive substrate is demonstrated. In fact, the heat liberated by the reactions involved is large enough to guarantee the self-sustaining character of the process within a wide range of reactants compositions. Moreover, no residual chlorinated organic compounds were found in the final solid product. Some reactor engineering aspects, as well as other significant future scientific and technological issues, are also addressed in view of large-scale applicability of processes based on self-propagating reactions. To date, the batch reactor technology seems to be more easily applicable, although the use of continuous reactors is not excluded in the next future.

Conversion of magnesium fluoride to magnesium hydroxide

The conversion of magnesium fluoride to magnesium hydroxide was studied as part of a process to bleed magnesium from zinc sulphate electrolyte. Most electrolytic zinc plants have to deal with accumulating magnesium in their process liquors as the natural magnesium bleed usually does not balance input from concentrates. The most common forced magnesium bleed produces large amounts of waste gypsum and could potentially be environmentally unfriendly. An alternative process was suggested and discussed, which involves magnesium fluoride precipitation from zinc electrolyte. The magnesium fluoride is converted to magnesium hydroxide in order to produce a saleable product. Regeneration of chemicals from the resulting sodium fluoride solution can be accomplished by means of an electro-dialysis process. Previous experiments indicated a relatively high residual fluoride content in the conversion product, which might limit the application possibilities of the magnesium hydroxide. From the experiments described in this paper it followed that it is not possible to reduce the residual fluoride content of the magnesium hydroxide product to <1 wt.% by optimising operating conditions such as leach concentration, reaction temperature, reaction time and wash procedures. From X-ray diffraction analysis, it was deduced that the residual fluoride was incorporated into the brucite crystal structure. Therefore, the sharp conversion of magnesium fluoride to magnesium hydroxide, derived from thermodynamic analysis, is in practice not entirely valid. It is possible to reduce the fluoride content of the product by burning the (fluoride containing) magnesium hydroxide to magnesium oxide (with <1 wt.% F) at temperatures of >1273 K. Thus a saleable product could be obtained.

Characterization of hydroxyl-bearing magnesium fluoride containing physically bound water

Most electrolytic zinc plants have to deal with dissolved magnesium in their process liquors, as zinc sulphide concentrates contain small amounts of magnesium. Applied magnesium bleed methods are generally expensive and environmentally unfriendly. Recently, a new approach was suggested and discussed, which involves selective magnesium fluoride precipitation from purified zinc sulphate solutions. X-ray fluorescence measurements of these precipitates indicated that the ratio Mg:F is not 1:2 as would be expected if the precipitate was MgF2, which should be formed on a theoretical basis. It was inferred that fluoride was partly substituted by hydroxyl groups. Analytical techniques such as infrared absorption spectrometry, X-ray diffraction, and thermogravimetry were combined in order to verify this hypothesis. The precipitate indeed appeared to be a magnesium fluoro- hydroxide compound containing physically bound water. The results contribute to the understanding of the required operating conditions of the proposed process.

Self-propagating reactions for environmental protection: state of the art and future directions

The major achievements obtained in the field of self-propagating reactions exploited for environmental protection are reviewed. In particular, the fixation and consolidation of high level radioactive wastes (RAWs), the treating and recycling of a highly toxic solid waste from electrolytic zinc plants, the recycling of silicon sludge and aluminum dross produced by semiconductor industries and aluminum foundries, respectively, and the degradation of chlorinated aromatics are addressed. Future scientific and technological directions related to this promising field of reaction engineering are foreseen.

Thermodynamic modelling of magnesium fluoride precipitation in concentrated zinc sulphate environment

Most electrolytic zinc plants have to deal with dissolved magnesium in their process liquors as zinc sulphide concentrates contain small amounts of magnesium. Applied magnesium bleed method are generally expensive and environmetally unfriendly. Recently, a new approach was suggested and discussed in which magnesium fluoride is selectively precipitated from purified zinc sulphate solutions by addition of zinc fluoride solution. Magnesium fluoride can be converted into magnesium hydroxide with sodium hydroxide solution and regeneration of chemicals is accomplished by electrolysis of the resulting sodium fluoride solution in a membrane cell. In this paper, a thermodynamic model of the precipitating system is evaluated in order to predict the residual fluoride content of the solution as a function of pH and temperature. This is an important parameter as residual fluoride can cause detrimental effects in the electrowinning stage (pitting of the aluminium chatodes). The model predictions are compared with experimental data. The presented thermodynamic model is a tool that contributes to the determination of the optimum precipitation conditions.

Self-propagating Reactions for Environmental Protection: Remarks on the Treatment and Recycling of Zinc Hydrometallurgical Wastes

A new method of treatment of a highly toxic solid waste from electrolytic zinc plants, i.e., goethite waste, based on self-propagating thermite reactions is proposed. This technique consists of ble...

Magnesium removal in the electrolytic zinc industry

Most electrolytic zinc plants have to deal with dissolved magnesium in their process liquors, as zinc sulphide concentrates contain small amounts of magnesium. Applied magnesium bleed methods are generally expensive and environmentally unfriendly. In this paper, a new approach is suggested and discussed in which magnesium fluoride is selectively precipitated from purified zinc sulphate solutions. The magnesium fluoride is contacted with sodium hydroxide solution and thus converted into magnesium hydroxide, which could be saleable product. It is shown that the resulting sodium fluoride solution can be electrolysed in a membrane cell consisting of a zinc anode and an inert cathode. This yields zinc fluoride and sodium hydroxide solutions, which both can be recycled to the magnesium removal process. Various experiments, which are discussed in this paper, confirm that the proposed process is possible.

Treatment and recycling of zinc hydrometallurgical wastes by self-propagating reactions

A novel technique for treating and recycling of a highly toxic solid waste from electrolytic zinc plants, i.e. goethite waste, is proposed. It consists of blending this waste with suitable amount of reducing agents (aluminum or aluminum and silicon) and ferric oxide, and igniting the resulting mixture so that a self-propagating reaction in the form of a combustion wave rapidly travels through the mixture without requiring additional energy. Reactants are converted into two solid products (P 1 and P 2) with different mass, composition and structure, and a gas constituted by SO 2. Aluminum and silicon should be preferred as reducing agents, since the reaction product P 1 obtained in larger quantity, is constituted by an amorphous glassy structure of alumino-silicates which embodies heavy metals, such as Pb and Cd. Leaching tests of the reaction products P 1 are also performed to verify the possibility of their disposal. The solid product P 2 on the other hand may be recycled in the roasting unit of the industrial zinc production plant. A waste treatment process is also proposed.

Adsorptive Stripping Voltammetric Determination of Germanium in Zinc Plant Electrolyte

Germanium is detrimental to the electrochemical deposition of zinc. Consequently, its concentration needs to be monitored in an electrolytic zinc plant. Pyrocatechol violet can be used as a complexing agent with germanium. Adsorption of the complex followed by reduction allows a sensitive differential pulse adsorptive stripping voltammetric method to become available for the determination of germanium at a hanging mercury drop electrode in zinc plant electrolyte. Interference in the determination of germanium can occur from the presence of cadmium, lead and zinc metal ions. Careful adjustment of the pH of the solution shifts the germanium -pyrocatechol violet wave to potentials where intereference is minimal. However, if the relative concentration of cadmium and lead are too high, then these ions can be separated from germanium ions by bulk electrolysis to their amalgams at a mercury pool electrode. The method developed has been applied to zinc plant electrolyte and ore samples.

Off‐line and on‐line differential pulse anodic stripping voltammetric techniques for the determination of antimony(III) and antimony(V) in zinc plant electrolyte

AbstractAntimony, in both its trivalent and pentavalent states may be detrimental to the electrochemical deposition of zinc. Ideally, therefore antimony should be monitored in both oxidation states throughout an electrolytic zinc plant. At hydrochloric acid concentrations ( &gt; 4 M) both antimony(III) and (V) present in zinc plant electrolyte can be reduced at a hanging mercury drop electrode (HMDE) to form an antimony amalgam, Sb(Hg). Consequently a very sensitive analytical signal is obtained for the determination of total antimony by differential pulse anodic stripping voltammetry (DPASV) using a 1:1 mixture of plant electrolyte and concentrated hydrochloric acid. In contrast, at low acid concentrations (0.1 M) predominantly only antimony(III) can be reduced and therefore determined in zinc plant electrolyte by DPASV at a HMDE by use of a 1:1 mixture of plant electrolyte and 0.2 M hydrochloric acid. The antimony(V) concentration is calculated by the method of subtraction of antimony(III) from total antimony. Consequently, simple addition of high and low concentrations of hydrochloric acid to zinc plant electrolyte can be used to provide a suitable electrolyte for both off‐line and on‐line methods for determining the concentration of total antimony, antimony(III) and antimony(V). The method described in this article has been applied to a wide range of zinc electrolyte samples and an on‐stream analyzer technique has been successfully used for several years at the Pasminco Metals‐BHAS electrolytic zinc plant in Port Pirrie, Australia.