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Room: 231A
Session Chairperson: Mrs. S. Young, BHP Copper Inc., 2400 Oracle Road, Suite 200, Tucson, AZ 85704
8:30 am
EFFECTS OF FLUID VELOCITY OF ELECTROLYTE ON COPPER ELECTROREFINING: A. Tsubouchi, T. Nakamura, F. Noguchi, I. Iakasu, Kyushu Institute of Technology, Department of Materials Science and Engineering, Kitakyushu, Japan 804
A high current density operation is desired to improve the productivity in copper electrorefining. However, a lot of problems still remain such as passivation of anode, dendritic deposition of cathode and contamination of impurity elements during the high current density electrorefining of copper. To clear the problems mentioned above, effects of the fluid velocity of the electrolyte on the morphology of copper deposition on cathode and the passivation behaviour of anode have been investigated at various current densities in the present study. Although a granular appearance of the copper deposition was obtained with increasing the current density, it was depressed by an increase of the fluid velocity of the electrolyte. Then an uniform deposition on the cathode was also observed when the fluid velocity of it became higher. Further more, no passivation behaviour of anode could be found by high speed circulating the electrolyte even in the high current density operation.
8:55 am
ENERGY SAVING IN COPPER ELECTROWINNING: C. Lupi, D. Pilone, Dip. ICMMPM, Università di Roma "La Sapienza", V. Eudossiana, 18, 00184 Roma, Italy
The energy consumption, in the electrowinning step of copper production by hydrometallurgical traditional process, generally represents more than 1/4 of the total energy requirement. The considerable saving can be achieved just in this step that requires about 8 GJ/tonne of the produced copper. To save energy the cell voltage, or more appropriately its anodic component, can be reduced: that is because the anodic voltage represents the main component of cell voltage and so it is responsible for the actual energy consumption in the copper sulphate electrowinning. In this work some ways are studied to lower the anodic voltage. First the cobalt ions were added to the sulphate solution in order to study the catalytic effect on oxygen discharge. Then lead alloys anodes (Pb-Ag, Pb-Sb-Ag and Pb-Ca) were used to promote a better oxygen evolution as a result of a different anodic surface. Their behaviour was compared with the Pb-Sb traditional ones. Finally, as already pointed out by several authors for zinc electrowinning, ethylene glycol was employed as anodic depolarizer in order to verify its effectiveness in the case of copper electrowinning. Combining all the above-mentioned ways energy saving ranging from 20% to 27% is achieved. All the tests were carried out on a laboratory pilot-plant for long time to simulate the industrial conditions. The obtained copper deposits were observed by SEM to highlight their morphology and were also analyzed by spectrometer to verify their purity.
9:20 am
NUMERICAL COMPUTATION OF ANODIC SLIME BEHAVIOUR IN COPPER REFINING CELLS: A Filzwieser, A. Lackner, K. Hein, P. Paschen, Department of Nonferrous Metallurgy, University of Leoben, A-8700 Leoben, Austria; K. Pachler, AVL List GmbH, A-8020 Graz, Austria
The fluid flow in a copper refining cell is calculated three dimensionally, using the CFD-software package FIRE. The simulation is based on density variations in the boundary layer at the electrode surface. Calculations and LDA-measurements are in good correspondence. The actual glue concentration in the cell is calculated, too. Moreover, a two phase flow approach is developed, based on the "Discrete Droplet Model" to simulate the behaviour of anode slime during electrolysis. The position, velocity and diameter of each anode slime particle is described. The computations show the dependence of slime particle size distribution, density and electrolyte circulation rate on the possibility of being included in the cathode copper or collected at the cell bottom.
9:45 am
INFLUENCE OF THE ELECTROCRYSTALLIZATION INHIBITORS DURING COPPER ELECTROREFINING: A NEW EXPERIMENTAL APPROACH: J.-L. Delplancke, M. Degrez, C. Temmerman, R. Winand, Université Libre de Bruxelles, Metallurgy, CP165, 50 Av. F.D. Roosevelt, B1050 Brussels, Belgium
The influence of the copper electrocrystallization inhibitors (mainly thiourea, gelatin and chloride ions) is studied in a new fully automatic pilot plan. This paper describes the conception and the building of this plan. The plan is in hydrodynamic similitude with an industrial copper electrorefining plan. Three cells with forced electrolyte flow may be connected in parallel or in series on order to model the copper production cells. The electrolyte is characterized chemically and electrochemically before and after electrolysis. One day and one week long experiments are performed. The structure of the deposits is characterized by SEM, EDX and metallographic cross-sections. The new approach for the study of these inhibitors is firstly to reproduce the experimental conditions observed in the industry with the three additives present simultaneously in the electrolyte and secondly to study the influence of a slight modification of the concentration of one inhibitor, the others being present in the electrolyte with their industrial nominal concentrations.
10:10 am
THE CHARACTERIZATION OF PASSIVATING FILMS ON COMMERCIAL COPPER ANODES USING IMPEDANCE SPECTROSCOPY: M.S. Moats, J.B. Hiskey, S.C. Campin, University of Arizona, Copper Research Center, Material Science and Engineering Department, College of Engineering and Mines, Tucson, AZ
Electrochemical techniques are a valuable means of analyzing the passivation of commercial copper anodes. Electrochemical impedance spectroscopy (EIS) provides information concerning transport and reaction phenomena occurring at an electrode surface. Commercial copper anodes of varying compositions have been examined using EIS. Experiments were conducted in a flat cell with an electrolyte of 40 g/l Cu2+ and 160 g/l H2SP4 maintained at 65°C. Impedance spectra were obtained at the potentials characteristic of the open circuit voltage and the passive region for each anode. The spectra of the passivating films exhibited a flattened resistive/capacitive loop at middle to high frequencies and an inductive loop at low frequencies. An equivalent circuit utilizing an inductor-resistor series in parallel with the double layer capacitance and charge transfer resistance was adequate in modeling the impedance data. The influence of anodes impurities on the components of the equivalent circuit is discussed and correlated with a bilayer passivation model.
10:30 am
SURFACE ROUGHENING OF ELECTROWON COPPER IN THE PRESENCE OF CHLORIDE IONS: E. Ilgar, P. Yu, T.J. O'Keefe, University of Missouri-Rolla, Department of Metallurgical Engineering and Graduate Center for Materials Research, Rolla, MO 65409-1170
A statistically designed screening test was carried out in the absence and presence of 20 ppm Cl- ions using a three factor, two-level factorial design in an electrolyte containing 36 gl-1 Cu2+ and 150 gl-1 sulfuric acid. The independent variables evaluated were agitation, current density and temperature; their influence on surface roughness was determined. Using the data generated, a model expression was developed to allow estimation of surface roughness of the copper deposits. X-ray diffraction, scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and profilometer techniques were used in the evaluation. The copper deposited at current densities where activation was the primary control mechanism appeared similar in morphology whether stirring was used or not. The addition of 20 ppm Cl- ions to the electrolyte gave rougher deposits under the same conditions. In the mixed control regions, where mass transfer effects were initiated, considerably rougher and more dendritic deposits were obtained when Cl- ions were present. Agitation was effective in reducing the copper surface roughness both in the apparent activation and mixed control regions in the presence of Cl- ions. The results of this study showed that 20 ppm Cl- polarized the copper deposition at low overpotentials but caused depolarization at higher overpotentials, and promoted roughening even where Cu2+ mass transfer was not a factor.
10:55 am
THREE-DIMENSIONAL CALCULATION OF CURRENT DISTRIBUTION IN ELECTRODEPOSITION OF COPPER: Y.S. Choi, N.S. Kim, S.H. Jeon, T. Kang, Seoul National University, Department of Metallurgical Engineering, Seoul, Korea; H.J. Sohn, Seoul National University, Department of Mineral and Petroleum Engineering, Seoul, Korea
The thickness uniformity of electrodeposits depends largely on the current density distribution over the cathode. The current distribution is determined by the geometrical characteristics of the electrodes and the cell, the polarization at the electrode surface and the mass transfer in the electrolyte. The calculation of the current distribution is possible by various numerical techniques, among which the boundary element method (BEM) is considered to be most efficient. In this study the program for the calculation of 3-dimensional current distribution by use of the BEM with a linear element of trigonal type was developed and applied to the rectangular cathodes in copper electroplating. For simplicity the anode potential was assumed to be constant and the nonlinear polarization curves obtained from the potentiodynamic experiments were fitted to a linear equation over the range of current densities, 20~80mA/cm2. The effect of the cell dimension and the anode shape on current distribution was simulated. The calculated values agreed fairly well with the measured values and the thickness uniformity could be improved by the proper combination of the cell geometry and the anode shape.
11: 20 am
THE SOUTHERN PERU ILO REFINERY, DESIGN FEATURES, OPERATION AND IMPROVEMENT: F. Begazo, W.A. Enrico, Southern Peru Limited, 180 Maiden Lane, New York, NY 10038
Southern Peru Limited's Ilo Refinery, the largest in Peru, began operations in 1975 with a production capacity of 165,000 stpy. Southern Peru bought the Refinery from the state owned Minero Peru S.A. on June 1, 1994. The refinery processes blister from Southern Peru's Ilo smelter. Blister copper is processed in an anode plant equipped with two 365 st. tilting reverberatory furnaces, a 26 mold casting wheel and an anode press machine. Copper is electrorefined in a tank house equipped with 768 commercial cells, 44 stripper cells and 40 liberator cells, utilizing two electrolyte circuits and a 21,000 ampere rectifier. During 1989 through 1994, a program for improving productivity was carried out by increasing the number of cells and increasing current density to the total rectifier capacity. As a result, a capacity of 215,000 stpy of refined copper, 2 million troy ounces of silver and 6,000 troy ounces of gold per year was achieved. In 1994, Southern Peru announced plans to increase the capacity to 250,000 stpy of cathode with a US$ 18 million investment and a US$2 million investment in environmental improvement projects, as part of the purchase agreement with the Peruvian government. This paper outlines the scope of the Southern Peru Limited refinery modernization and environmental program. It describes the implementation of the electrolytic plant expansion based on installation of polymer concrete cells, a new rectifier, a new selenium roaster and a precious metal plant upgrades.
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