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Room: 231A
Session Chairperson: Dr. E. Ozberk, Sherritt International, Bag 1000, Fort Saskatchewan, AB, T8L 2P2
2:00 pm
DEVELOPMENT OF AUTOMATIC MATERIAL HANDLING AND MONITORING SYSTEMS IN AN EXISTING ELECTROLYTIC ZINC PLAN: T. Yamada, R. Togashi, T. Aichi, Akita Zinc Co., Ltd., Hjima Refinery, Akita, Japan
Mainly due to the strong yen and the relatively low metal price, the zinc refineries in Japan are being forced to reduce man power. At IIjima, a new automatic material - handling system for cathode transportation was developed and the first system went to service in August 1994. The work was started in 1993 and all installation will be finished in the summer 1997. The critical part of this work was to achieve the designed cycle time because of the fairly complex cell-layout. As the cathodes are placed opposite direction in every other unit, cranks must be able to move toward two directions (X and Y) at the same time and to stop precisely at the tolerance level of a few millimeter. The central monitoring system for machine operation run by an original application software with MICROSOFT EXCEL© on WINDOWS 95©, was started in June 1996. There had been one person only for operating a manual crane before. Now an operator of a stripping machine can control the automatic crane for the same row at the same time. As a result, only one person can operate both a crank and a stripping machine for one row. And more labour saving is expected in the future.
2:25 pm
INDUSTRIAL SIZE "PLACID ELECTROWINNING CELL": C.Frías, M.A. García, G. Díaz, Tecnicas Reunidas, S.A., R & D Centre, Madrid, Spain
Under the auspicious of the Commission of the European Union, a consortium composed of six European organizations has developed the PLACID process, into the Brite Euram II Programme. The project began on January 1993 and was finished on April 1996. The PLACID process is based on a novel technology able to deal with different lead bearing materials, mainly lead oxide secondaries: Lead-acid batter pastes, lead fumes, furnace slags, oxide residues, etc., producing "four nines" pure lead in an efficient manner with a benign influence on the environment. In the PLACID process, lead is leached in warm, slightly acidic, brine to form soluble lead chloride. This solution is purified by cementation with lead powder. Pure lead is then won from the lead chloride electrolyte on the cathode of the electrowinning cell and is collected. This electrolytic cell is the heart of the process and it was especially developed to give optimum performance. Hydrochloric acid is reformed in the cell and returned to the leaching bath; reagent net consumption in the process is irrelevant. This paper is concerning the development of the PLACID electrowinning cell up to industrial size electrodes. The performed work has covered three levels of development: laboratory study, bench scale experimentation and pilot plant prototype testing (16 Kg/h electrolytic lead production). After 1,000 hours operating time, the achieved results of the pilot plant electrowinning cell have been very satisfactory, demonstrating the ability of the Placid electrowinning cell to produce top quality electrolytic lead (above 99.99% Pb) with high current efficiency and low energy consumption.
2:50 pm
CHARACTERIZATION OF ANTIMONY-GELATIN ADDITIVES IN ZINC SULPHATE ELECTROLYTES USING IMPEDANCE ANALYSIS: X. Tang, Southwire Copper Division, 372 Central High Rd., Carrollton, GA 30117; P. Yu, T.J. O'Keefe, University of Missouri-Rolla, Department of Metallurgical Engineering and Graduate Center for Materials Research, Rolla, MO 65409-1170; G. Houlachi, Noranda Technology Centre, Pointe-Claire, Quebec, H9R 1G5, Canada
Impedance measurements were used to investigate the electrochemical characteristics of acidic zinc sulphate electrolytes containing Sb3+, gelatin and their mixtures. The data were correlated with cyclic voltammetry curves made using synthetic as well as industrial electrolytes. The cyclic voltammetry results were similar to those obtained in previous studies in that antimony caused a depolarizing effect while gelatin gave an increase in the potential for zinc nucleation on an aluminum substrate. The electrochemical impedance spectroscope (EIS) evaluations were conducted on electrodeposited zinc at three overpotential values. The potentials were chosen to represent various current density regions in the zinc polarization curves. The antimony and gelatin gave characteristic impedance plots which correlated with expected behaviour, particularly current efficiency. Both antimony and glue appear to modify the intermediate zinc reaction sequence, but in different ways. The data strongly suggest that film formation and stability are major factor in the zinc ion reduction mechanism.
3:15 pm
EFFECTS OF ANTIMONY AND CONTINUOUS GELATIN ADDITION ON CURRENT EFFICIENCY IN THE HUDSON BAY ZINC ELECTROWINNING TANKHOUSE: P. Merrin, Hudson Bay Mining & Smelting Co., Limited, Flin Flon, Manitoba, R8A 1N9, Canada
This study was conducted at Hudson Bay Mining and Smelting's zinc electrowinning tankhouse to determine the effects of varying levels of antimony and continuous gelatin addition on current efficiency. The levels of antimony and gelatin were varied between 0.010-0.030 mg/l and 0-10 mg/l respectively, using the fresh electrolyte as reference. The test was designed to determine the optimum operating point for current efficiency, and to investigate any interaction that occurs between the two components. An non-linear mathematical model relating these three variables was produced, giving an optimum operating point of 6.5 mg/l of gelatin and increasing current efficiency with decreasing antimony levels. Individually, the antimony concentration was approximately linear with current efficiency, while gelatin concentration was parabolic. An interaction term is present but is not significant enough to improve the ability of the tankhouse to handle purification upsets in antimony.
3:40 pm
THE EFFECTS OF SOME FOAMING REAGENTS ON ACID MIST CONTROL AND ZINC ELECTROWINNING FROM KIDD CREEK ZINC ELECTROLYTE: A.M. Alfantazi, D.B. Dreisinger, University of British Columbia, Department of Metals and Materials Engineering, Vancouver, B.C., V6T 1Z4, Canada; J. Synnott, M. Boissoneault, Falconbridge Ltd., Kidd Creek Division, P.O. Bag 2002, Timmins, Ontario, P4N 7K1, Canada
The effects of five commercially available foaming reagents (range of 0 to 25 ppm) namely Dowfroth 250 Saponin, Yucca, Licorice and Meta-Para Cresol on acid mist control, current efficiency, polarization behaviour, and deposit morphology and orientation were investigated using a bench scale electrolysis apparatus (cell volume 3L). The deposition was carried out at 500 Am-2 and 38°C for 3 hours from Kidd Creek zinc electrolyte. The acid mist control capability of the various reagents was studied and compared by characterizing the foam layer generated during actual electrowinning conditions and by direct quantitative measurements of acid mist levels on top of the electrowinning cells. Within the range considered, the addition of these reagents reduced the current efficiency, refined the grain size of the deposit, and changed to preferred orientation of most of the deposits. Among the reagents tested, acid mist measurements indicated that Licorice and Dowfroth 250 were the best acid mist suppressant at emissions of 0.30 mg/m3 and 0.31 mg/m3 respectively while Yucca and MPC produced the most mist at 3.0 mg/m3 and 3.3 mg/m3 emission rates respectively.
4:00 pm
ELECTROPURIFICATION OF ZINC LEACHING SOLUTION: S. Yamashita, K. Hata, S. Goto, Department of Metallurgy, Chiba Institute of Technology, Chiba, Japan
The average consumption of zinc dust for purification of zinc leaching solution is more than 25 kg per ton of electrolytic zinc. Authors proposed to remove impurities in zinc leaching solution by electrolysis instead of cementation by zinc dust. The effects of copper and arsenic on electrodeposition of cobalt in zinc sulfate solution were examined fundamentally by using potentiostat. The mesh cathodes of stainless steel and lead anodes are used in the electrolytic cell for removal of cobalt and an electrolyte is circulating rate of electrolyte, concentration of copper and arsenious ions on removal of cobalt are studied. Removal of Ni, and Cd are also examined.
4:25 pm
Cl ANION ELIMINATION FROM Zn SULPHATE SOLUTION BY PERIODICAL REVERSE ELECTROLYTIC SYSTEM: T. Yoshida, M. Kahata, M. Dobashi, M. Suzuki, Mitsui Mining and Smelting Co. Ltd., Sairama, Japan
In Japan, almost 30% of steel is produced by electric arc furnace (EAF) melting of iron scrap. And the dust from EAF includes approximately 20-30 wt % of Zn and 3.5 wt % of C1. They are treated as industrial waste to recover Zn as Zn oxide mainly by pyro metallurgical process. On the other hand, high purity zinc recovery by direct hydro-metallurgical processing is one of the most effective method. In this case, Cl in the EAF dust is dissolved in liquid phase by leaching, but the Cl anion in electrolyte attacks anode which is made of a lead base alloy. Several processes have been proposed to remove Cl anion from acidic sulfate solution. In this study, an electrolytic process is established to eliminate Cl anion from Zn sulfate electrolyte. It is known that Cl anion can be removed by anode oxidation. From our study it can be said that the elimination rate of Cl anion depend on the anode material, i.e. the elimination rate is Pb - Ag alloy > Pb DSE. Furthermore in industrial electro-winning process, electrolyte includes Mn dioxide. Therefore, the effect of Mn in electrolyte should also be considered for Cl elimination. It seems that Mn dioxide deposition on anode decreases the efficiency of Cl anion removal. The periodical reverse system was induced to prevent from efficiency decrease. By using periodical reverse system, deposited Mn dioxide is removed very rapidly when the current was reversed for short time. More than 95% of Cl anion can be removed in extremely short period than conventional method. At the symposium the detailed data will be presented about Cl anion elimination by periodical reverse system.
4:50 pm
THE ROLE OF COPPER AND ANTIMONY ADDITIVES IN THE REMOVAL OF COBALT FROM ZINC SULPHATE SOLUTIONS: V. Van der Pas, D. Dreisinger, University of British Columbia, Department of Metals and Materials Engineering, Vancouver, British Columbia, V6T 1Z4 Canada
Zinc sulphate electrolyte used for zinc electrowinning must be purified for cobalt ions. The cobalt is removed in a cementation stage by the addition of zinc dust. Copper and antimony are frequently used additives which enhance the cementation of cobalt. This paper aims at a better understanding of how copper and antimony promote the removal of cobalt. Initial experiments were done in a batch cementation reactor. Copper and antimony precipitated in the early stages of cementation indicating that a preferential substrate was formed. The individual role of copper and antimony was further investigated in an electrochemical cell. On a microscale, the growth process, morphology and the composition of the precipitates under various conditions were examined with SEM and XRD. It was found that cobalt could not be deposited in its pure form but as a cobalt-zinc alloy with zinc as the prime constituent. The effect of copper addition is of increasing the cathodic surface area of zinc dust by precipitating as numerous dendrites. Antimony acts as a cathodic surface onto which a cobalt-zinc alloy with an increased cobalt content is deposited.
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