Spouted bed electrowinning of zinc: Part II. Investigations of the dynamics of particles in large thin spouted beds
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TRODUCTION
PART I of this two-part article has described a laboratory-scale investigation of the spouted bed electrode (SBE), as employed for the electrowinning of zinc from acid sulfate electrolytes akin to those presently used in industrial practice. The results of that investigation were encouraging in that zinc could be electrowon with direct current electrical energy consumption of less than 3 kWh/kg at current densities a factor of six greater than in conventional cells. However, the beds employed in the investigation were 10to 20-cm high and 6- to 10-cm across, and it was thought necessary to examine the dynamics of the particles and electrolyte in much larger beds. In particular, it was necessary to address the question of whether particles could be reliably circulated in beds of a size, perhaps 1 to 2 m 3 1 to 2 m, likely to be employed in any commercial exploitation of the SBE. Of special significance was the behavior of beds of this large size that were nevertheless thin. In Part I, it was shown that ‘‘flat’’ cells approximately 20-mm thick yielded the good performance referred to previously. This geometry, small in one horizontal dimension but large in the other and in the vertical dimension, is unusual for spouted beds. Such a bed has been examined previously by Mujumdar[1] and Raghavan and Mujumdar[2] and by Passos et al.[3] for the drying of grain, apparently with the wish to have a modular unit that can be scaled up to the necessary capacity by stacking units together. Large industrial spouted beds, such as those used for drying of grain or chemical reaction of coarse particles, are usually large in all three dimensions.[4] Furthermore, draft tubes employed in the SBEs of Part I are not common in spouted beds[5,6] A. VERMA, formerly Graduate Student, Dept. of Materials Science and Mineral Engineering, University of California, Berkeley, CA 94720, is Applications Engineer, Solid State Measurements, Pittsburgh, PA 15275. J.W. EVANS, Professor of Metallurgy, is with the Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA 94720. JUAN CARLOS SALAS-MORALES, formerly Graduate Student with the Department of Materials Science and Mineral Engineering, University of California, is with Superintendencia de Investigacion Y Desarrollo, Chuquicamata Division, Codelco Chuquicamata, Chile. Manuscript submitted January 30, 1996. METALLURGICAL AND MATERIALS TRANSACTIONS B
but were believed necessary in the present investigation to permit the high ratio of height to thickness thought preferable for electrochemical cells. The investigation started with laboratory-scale beds of cylindrical cross section and followed with a study of a (nominally) 2-m-high bed that was up to 0.35-m wide and equipped with one draft tube. Preliminary experiments were carried out on a 1-m high 3 2-m wide bed fitted with multiple draft tubes. II.
LABORATORY-SCALE BEDS
Figure 1 depicts the laboratory spouted bed used for investigating the particle and liquid dynamics at this scale. The apparatus was
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