A STUDY ON THE SCALE-UP OF A STIRRED-TANK EXTRACTOR FOR A LIQUID SURFACTANT MEMBRANE PROCESS

An experimental work of copper extraction using a tank of 35 dm(3) (li quid volume 16 dm(3)) volume was carried out for the scale-up of a sti rred tank extractor for a liquid surfactant membrane process. In the e xperiment, kerosene solution containing 1-7 vol. % Span 80 and 1-10 wt % LIX 64 N was used as the oil phase. 15.7 mol . dm(-3) copper sulfat e solution of pH 5.4 and 0.38 mol . dm(-3) or 0.5 mol . dm(-3) sulfuri c acid solution were used as the outer and the inner aqueous phase, re spectively. The extraction rate, the break up ratio of the W/O emulsio n, and the mechanical entrainment were measured. As a result of a smal l scale volume, the extraction rate was expressed by the following Equ ation -(d ln C-cu-out/d theta) = k' . C-L . C-s(-0.32). W-e(0.3)/(C-H( +))(0.5) Where k' = 6.9 X 10(-5) m(1.5). mol(-0.5). s(-1), C-cu.out is copper concentration in the outer aqueous phase, C-L is weight fracti on of extractant in kerosene, C-s is volume fraction of surfactant in kerosene, theta, extraction time, W-e, Weber number, D, diameter of im peller, N, agitation speed, rho(c), density of outer water, sigma, sur face tension and C-H(+) is concentration of hydrogen ion. The optimum conditions of a middle scale tank were as follows, (1) agitation speed is 2.8 s(-1), (2) pouring rate of the emulsion should be less than 8. 33 cm(3) . s(-1), (3) surfactant concentration is 2 vol. % (about 2.5 wt. %), (4) extractant concentration is 3 wt. %. Under optimum conditi ons, more than 99.9% of copper in the feed solution was extracted in 1 0 min., the break up ratio was less than 2% and the mechanical entrain ment was less than 8 vol. %. The extraction rate was expressed by the same equation as in the small scale. The entrainment occurred mainly i n the phase separation.