The electrophoretic mobility of hexane droplets dispersed in aqueous solution has been investigated in the presence of mixed extractant systems consisting of anti-5,8-diethyl-7-hydroxy-6-dodecanone oxime (the active extractant in LIX63) + dinonylnaphthalenesulfonic acid (HDNNS), di(2-ethylhexyl)phosphoric acid (HDEHP) + HDNNS, and tricaprylylmethylammonium chloride (Aliquat 336) + HDNNS. LIX63 was found to lower the electrophoretic mobility of HDNNS-hexane droplets, an additive effect in electrophoretic mobility was seen in HDEHP + HDNNS systems, while the presence of Aliquat 336 in HDNNS solution reversed the interfacial charge from negative to positive. The effects of aqueous metal ions, Ni(II), Co(II) and Fe(III), on the electrophoretic mobility of LIX63-, HDNNS- and LIX63 + HDNNS-containing hexane droplets were also investigated. It was found that the effects of these metal ions are strongly pH-dependent. Charge reversals (CRs) were generally observed in the pH range 9-11 for Ni(II)- and Co(II)-containing systems, and in a wider pH range (3-11) for Fe(III). The first CR is attributed to a partial coating of the oil drops by metal hydroxide precipitates, while the second CR reflects the behavior of a completed surface layer of metal hydroxide precipitate.
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