Application of ultrasound in extractive metallurgy: Sonochemical extraction of nickel
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INTRODUCTION
U L T R A S O U N D assists heterogenous processes such as flotation, r~l leaching, ~zj electrometallurgy, t3~ filtering, I41 drying, ~51 and others. It is believed that cavitation (bubble formation and implosion), microstreaming, radiation pressure, acoustic pressure, and degassing account for ultrasound's advantages. Solvent extraction is another typical heterogenous system that involves two distinct and immiscible phases. In such a system, ultrasound, because of its compression and expansion, can tear the liquid droplets, increasing the contact area between the immiscible organic and aqueous phases through emulsion and dramatically increasing the rate of extraction. In addition to its emulsifying effect, ultrasonic energy further increases solvent extraction through (1) enhanced local agitation, (2) induced-circulation currents, (3) prolate-oblate oscillations inside the liquid drop, and (4) the removal of stagnant liquid near the interface between the organic and aqueous phases. [6~ Most of the studies on solvent extraction with ultrasound have been done on nonmetallic liquid-liquid extraction systems, those controlled by mass transfer. Only a few studies have been done on the solvent extraction of metals, f6,7,8] However, many systems for solvent extraction of metal are controlled by chemical reaction mechanisms that may also benefit from ultrasound. To study the role of ultrasonic energy in solvent extraction, two typical chelating solvent extraction systems were selected, one acidic and the other strongly basic. The basic system was used in the extraction of gallium with Kelex 100, as reported earlier by Pesic and Z h o u . [9] The present work studies the role of ultrasound on solvent extraction of metals from acidic solutions. The solvent extraction of nickel with hydroxyoxime extractants
BATRIC PESIC, Associate Professor of Metallurgy, and TAILI ZHOU, Research Associate, are with the College of Mines, University of Idaho, Moscow, ID 83843-4199. Manuscript submitted March 11, 1991. METALLURGICAL TRANSACTIONS B
was selected for study because of nickel's slow rate of extraction. The hydroxyoxime-carboxylic acid system for the selective extraction of nickel from cobalt in acidic sulfate solutions was first recommended by Flett and West. ~t~ They found that when carboxylic acid was added to c~-hydroxyoxime (Lix 63), a synergistic effect occurred, increasing the yield of nickel significantly. However, the rate of extraction was so slow that it took about 3 hours to reach equilibrium, a phenomenon that may be linked to the presence of carboxylic acid at the interface, as indicated by the interracial tension determination.[~ L,~2,13] However, because of the complicated extraction mechanism, the slow extraction rate of nickel was not fully explained. Several ways to increase the extraction rate have been suggested. Nyman and Hummelstedt ~41 reported that the type of diluent and its temperature considerably influenced the extraction rate. They suggested the addition of a D N N S A (dinonylnaphth
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