Nondispersive liquid-liquid extraction of Zn(II), Cu(II), Co(II), and Cd(II) from dilute solution with dehpa in a hollow-fiber membrane module

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.