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The ability to concentrate dilute aqueous solutions containing metals is desirable both from the standpoint of waste volume reduction and increased ease of concentration measurement. The first challenge in designing a liquid-liquid extraction (LLE) system to concentrate metals is to find an organic system that can be used to simultaneously remove a number of metals. The goal of this work was to find a LLE system that extracts zinc, copper, cadmium and cobalt simultaneously. In the LLE extraction experiments, nearly 100% extraction of all four metals (Zn(II), Cu(II), Cd(II) and Co(II) at about 25 ppm initially) was achieved when all of them were extracted simultaneously using 0.3 mol/L DEHPA in n-heptane. The extraction order observed as the pH of the aqueous solution increased was Zn(II) > Co(II) > Cu(II) > Cd(II). Based on these results, a polysulfone Hollow Fiber Contained Liquid Membrane (HFCLM) system was designed and operated to study the nonequilibrium extraction of all four metals via nondispersive LLE. The aqueous and organic streams were operated at 100% recycle. Interference effects between the four metal ions are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A liquid-liquid extraction procedure was used to study the amounts of Zn2+ and Cu2+ that could be simultaneously extracted from aqueous solution with di(2-ethylhexyl) phosphoric acid (DEHPA) and LIX 984 diluted with n-heptane at equilibrium. LIX 984 is a 1:1 volume blend of LIX 860 (5-dodoecylsalicylaldoxime) and LIX 84 (2-hydroxy-5-nonylacetophenone oxime). At equilibrium, a 0.3 mol/L DEHPA-20% (v/v) LIX 984 solution extracted 99% of both the zinc and copper from a solution that had 100 ppm of each metal. A polysulfone hollow-fiber membrane module with 1 mm ID and 5,000-molecular weight cutoff was used to study the amounts of Zn2+ and Cu2+ that could be simultaneously extracted with a mixture of DEHPA and LIX 984. The aqueous and organic streams were operated at 100% recycle. With a 0.6 mol/L DEHPA–10% (v/v) LIX 984 solution, a 90.5 ± 1.7% (s.d) extraction of zinc and a 93.70 ± 0.79% (s.d.) extraction of copper was obtained after 180 min. [ABSTRACT FROM AUTHOR]