Sponsored by: EPD Aqueous Processing Committee
Program Organizer: Professor David Dreisinger, The University of British Columbia, Department of Metals and Materials Engineering, 309-6350 Stores Road, Vancouver, B.C., C V6T 1Z4
Monday, AM Room: A14-15
February 5, 1996 Location: Anaheim Convention Center
Session Chairperson: Dr. Arash Kasaaian, Research Electrochemist, Elkem Metals Co., PO Box 299, Marietta, OH 45750
SPOUTED BED ELECTROWINNING OF COPPER AND ZINC: S. Siu, J.W. Evans, University of California, Department of Materials Science and Mineral Engineering, Berkeley, CA 94720; J. Salas, CODELCO Division Chuquicamata, Chuquicamata, Chile; M. Newman, Pasminco Research Center, Boolaroo, New South Wales, Australia
Prior investigations into fluidized bed electrowinning (FBE) have shown good results for copper but rather poor current efficiencies and high energy consumption rates for zinc (electrowon from conventional acid electrolytes). This paper describes an alternative electrode, the spouted bed electrode (SBE) which, in laboratory-scale investigations, appears superior to both FBE and conventional electrowinning. Current efficiencies and cell voltages comparable to those of conventional cells were achieved at current densities greatly in excess of those used in conventional cells for both copper and zinc. The paper describes the results of measurement of SBE cell performance as a function of electrolyte composition, particle size, current density and other experimental parameters. Preliminary work oriented towards cell scale-up is also described.
NEURAL NET MODELLING OF ZINC ELECTROWINNING PROCESS: D.H. Rubisov, V.G. Papangelakis, University of Toronto, Department of Chemical Engineering and Applied Chemistry, Toronto, Ontario, Canada M5S 1A4; G. Houlachi, C. Bowen, Noranda Technology Centre, 240 Hymus Boulevard, Pointe-Claire, Quebec, Canada H9R 1G5
The neural networks modelling approach is one of the most elegant black-box type methods to model industrial processes. In the paper, this approach is applied to model the performance of the zinc electrowinning process. The model that was built was found to exhibit an excellent predictive ability for voltage and current density. The model was also used to investigate the sensitivity of the process to various key variables such as temperature, current density, zinc and sulphuric acid concentration, etc. Optimal regimes for zinc production were identified from the power consumption standpoint.
RECENT OPERATION IN TANKHOUSE OF TAMANO SMELTER: Y. Oda, M. Kusano, K. Noda, Hibi Kyodo Smelting Co., Ltd., Copper Refinery, Tamano Smelter, No. 6-1-1 Hibi, Tamano City, Okayama Pref. 706, Japan
The tankhouse of Tamano Smelter has adopted a high current density electrolysis operation applying PRC (Periodic Reverse Current) method and before 1991, it has reconciled both high production capacity of 161,000 tons/year and high labor productivity. However, recent rapid rise of Japanese currency in foreign exchange market has urged us to further exert our efforts in reduction of labor cost. In order to achieve this goal of labor cost reduction, we have completed, in 1994, our phase four production expansion project which incorporated significant re-structuring of the organization and accomplished annual production of 191,000 tons/year. This project can be outlined as increase of number of cells for electrode exchange per day in the commercial electrolysis section to meet the increased number of cells and increase of the capacity of impurity treatment section. These improvements were done with minimum installation of new equipment and facilities and with achievements in efficiency and manpower saving of the existing facilities. Together with these improvements, rationalization in the start sheet section was carried out by changing the material for mother blanks as well as changing their maintenance procedures. At the same time, the crane in this section was modified to enable automatic operation by a fuzzy control. As a result, we were able to save manpower equivalent to 5 operators in this section. With these improvements, the production capacity has been increased by 18% and labor productivity by 25%.
IMPROVEMENT OF THE PERFORMANCE OF ANODES FOR ZINC ELECTROWINNING: J.M.S. Rodrigues, Mintek, Hydrometallurgy Division, Private Bag X3015, Randburg, South Africa 2125
The use of sandblasting for preconditioning anodes made from two different lead-based alloys for zinc electrowinning was investigated and compared with conventional fluoride preconditioning. Laboratory results showed that sandblasting and preconditioning both accelerated the formation of stable PbO2 layers on the anode and reduced oxygen overpotentials. The oxygen overpotential was lower on the lead alloy containing silver and calcium than on that containing silver only. It was found that sandblasting improved the physical stability of the lead dioxide layer compared with that obtained by fluoride treatment. This procedure was tested on an industrial scale in the cell house of a local zinc producer and in addition to confirming the laboratory results, corrosion rates of the lead anodes were established. An unexpected finding of the large scale tests was that the sandblasting appeared to work harden the lead anodes reulting in reduced warping during handling and operation. Sandblasting is easier to implement on a plant scale as no electrolysis or chemical treatment is required and the operation can be completed in a much shorter time.
THE REGENERATION OF HYDROCHLORIC ACID IN A TWO MEMBRANE NICKEL CHLORIDE ELECTROWINNING CELL: L. Liao, A. van Sandwijk, G. Van Weert, Delft University of Technology, Department of Raw Materials Technology, Faculty of Mining and Petroleum Engineering, Mijnbouwstraat 120, 2628 RX Delft, The Netherlands
During electrowinning of nickel chloride, hydrochloric acid instead of chlorine was regenerated in a two membrane cell, by segregating the chloride catholyte with an anion exchange membrane, and the sulphate anolyte with a cation exchange membrane form the middle electrolyte (ampholyte) compartment. Successful operation of such a cell depends on controlling chloride leakage through the cation exchange membrane to the anolyte. Small amounts of chlorine gas could be detected in the oxygen evolved at the anode. In this paper, the chloride leakage as function of various types of cation exchange membrane and different composition of the anolyte is reported and discussed. Ag+ was added to the anolyte to eliminate chloride leakage to the anode. The cell voltage, electrode potential and voltage drop over the membrane as function of current density has also been investigated.
OPERATION OF THE MCLE (MATTE CHLORINE LEACH ELECTROWINNING) PLANT FOR NICKEL REFINING AT SUMITOMO MOTAL MINING CO., LTD.: S. Makino, M. Sugimoto, F. Yano, N. Matsumoto, Niihama Nickel Refinery, Sumitomo Metal Mining Co., Ltd., 3-5-3, Nishibara-cho, Niihama, Ehimo, Japan
Sumitomo Metal Mining developed a new nickel refining process (MCLE process) based on chlorine leaching and electrowinning technologies and started the operation of the pilot plant with product capacity of 4,000 tons per year of cathode nickel in 1989. Then the commercial plant with design product capacity of 24,000 tons per year was constructed and has been successfully operated since August, 1992. Today the refinery product capacity is increased to 30,000 tons per year. Through these operations our MCLE process has been demonstrated to be one of the mot superior processes in the world with productivity, cathode quality and working environment. This paper describes the equipments and operation of the Sumitomo's MCLE process.
GOLD UPTAKE BY PYRITE IN BROMIDE SOLUTION: M. Fofana, Dept of Mineral Engrg, K. Osseo-Asare, Dept of Matls Sci & Engrg, Pennsylvania State University, University Park, PA 16802
The uptake of dissolved gold by pyrite in aqueous gold (III) bromide solution
was investigated as a function of pH (1 to 12), ionic strength (0.0 to 0.5M)
and time, using various surface and solution chemical techniques, including:
(a) zeta potential measurements, (b) atomic absorption spectrophotometry (AA),
(c) ion chromatography (IC),and (d) ultraviolet-visible spectroscopy (UV-Vis.).
Gold uptake was constant (99% gold removal) up to pH-9, and then decreased with
further increase in pH. The trend is rationalized in terms of the combined
effects of gold speciation, specific chemical interactions, and repulsive
electrostatic interactions. The relatively high gold removal at low pH
indicates that the pyrite surface can be a major source of gold loss during
bromine leaching of sulfidic gold ores. Also, the high extent of gold removal
even for extremely low pyrite quantities (e.g., 1 mg of Au removed/mg of
pyrite) can adversely affect the efficiency of industrial operations. The
substantial gold removal from solutions of high pH values and high ionic
strength also demonstrates that the pyrite surface can be efficient at
scavenging gold eve at high pH.
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