Stripping of Zn(II), Cu(II), Co(II), and Cd(II) from DEHPA using EDTA in a hollow-fiber membrane module

The equilibrium behavior of liquid-liquid extraction of Zn(II), Cu(II), Co(II), and Cd(II) from DEHPA (di(2-ethylhexyl)phosphoric acid) with EDTA (ethylenediamine-tetraacetic acid) was studied. A concentration of 0.003M EDTA was able to extract simultaneously 83, 70, 88 and 54% of the cadmium, cobalt, copper and zinc, respectively at a pH between 1.6 and 1.8. The non-equilibrium liquid-liquid extraction behavior was studied using a polysulfonic hollow fiber membrane module with 1 mm ID and 5,000 molecular weight cut-off. The aqueous feed solution and EDTA was passed through the tubeside of the two membrane modules, and the organic DEHPA solution was circulated through the shellside. The optimum flow rate for the organic solution was 77ml/min and that of the aqueous feed and strip solutions were 78ml/min. The shellside pressure was maintained at 1.0-1.2 psig and that of the tubeside was kept at atmospheric pressure so that a stable organic interface was achieved. Under these conditions, 77, 63, 93, and 56% of cadmium, cobalt, copper and zinc were extracted from DEHPA, respectively.