NOVEL MEMBRANE-BASED SYNERGISTIC METAL EXTRACTION AND RECOVERY PROCESSES

Individual metal recovery and separation by solvent extraction has bee n an important technique in pollution control as well as in hydrometal lurgical processes. Synergistic extraction and separation of two catio ns, e.g., Cu(II) and Zn(II), a cation and an anion, e.g., Cu(II) and C r(VI), and two cations and one anion, such as Cu(II), Zn(II), and Cr(V I), have been demonstrated employing a novel hydrophobic microporous h ollow fiber membrane-based (HFM) extraction technique. The extraction selectivity of Cu(II) and Zn(II) by LM 84 (anti-2-hydroxy-5-nonylaceto phenone oxime) and bis(2-ethylhexyl)phosphoric acid (D2EHPA), respecti vely, in a two-fiber-set HFM extractor is significantly enhanced due t o competitive extraction. The efficiencies of extraction of Cu(II) and Cr(VI) by LIX 84 and tri-n-octylamine (TOA), respectively, are increa sed due to the self-control of the aqueous feed pH. A simplified mathe matical model for synergistic extraction of Cu(II) and Zn(II) has been developed. The model predicts the observed extraction and separation performance well. In the novel HFM extractor, the extraction rates of Zn(II) and Cu(II) by D2EHPA and LM 84, respectively, were controlled b y the aqueous and organic boundary layer resistances as well as the in terfacial reaction resistances.