Strategies for optimal operation of the tellurium electrowinning process
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I.
INTRODUCTION
IN an increasingly competitive marketplace, operating a process at peak efficiency is not only highly desirable but a question of survival. The market for high-purity metals is a case in point. Until recently, tellurium was stockpiled as a by-product of other metal-winning processes such as, in particular, that of copper. However, the recovery of highpurity tellurium is rapidly becoming a highly profitable business, with market prices exceeding $50 US/lb. In order to take full advantage of this market opportunity, a technically efficient and economical strategy for the recovery of tellurium from TeO2 must be developed. Furthermore, the allowable levels for impurities such as lead and selenium in the electrowon tellurium must be exceedingly low for the product to qualify as an electronics-grade material. Having received limited attention, Te has been the subject of only a few technical articles, and these have, above all, focused on the fundamental electrochemical behavior of high-purity solutions. Jamieson and Perone,[1] for example, compared the use of polarographic, coulometric, and stationary electrode methods to define the behavior of (41)state Te in alkaline solutions. Strategies for the recovery of Te from highly contaminated electrolytes have not been addressed, nor has any structured statistical study of the process been reported. In the present work, rigorous statistical methods are used to prepare and analyze the data from a series of pilot-plant electrowinning trials. Empirical models of Pb and Se codeposition have been constructed and are used to identify process conditions which minimize tellurium contamination. An empirical model describing energy consumption has also been developed and is used GORDON BRODERICK, Senior Scientist, is with the Noranda Technology Centre, Pointe Claire, PQ, Canada H9R 1G5. BERNHARD HANDLE, Doctoral Student, is with Department of Metallurgical Engineering, McGill University, Montreal, PQ, Canada H3A 2B2. PETER PASCHEN, Professor, is with the Institute for Non-ferrous Metallurgy, Montan-University Leoben, 8700 Leoben, Austria. Manuscript submitted July 16, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
concurrently with models for Pb and Se codeposition to identify operating regimes which produce optimal process efficiency. II.
EXPERIMENTAL
A laboratory-scale electrolytic cell was used to extract Te from a feed solution. The cell was constructed of PLEXIGLAS* and had two anodes and a single cathode, with a *PLEXIGLAS is a trademark of Rohm & Haas Company, Philadelphia, PA.
deposition surface of 210 cm2 and a fixed electrode spacing of 2.5 cm. Each electroplating trial was conducted over a 2-hour period, with an initial contamination of approximately 1.6 pct selenium and 0.07 pct lead as a weight ratio on tellurium input in the electrolyte feed. Further details may be found in the article by Handle.[2] Experimental conditions for each trial were set in accordance with a central composite statistical design (CCD) consisting of N 5 36 trials. Five disti
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