Extraction of Zn(II), Cd(II), and Hg(II) by dodecyloligo(oxyethylene) carboxylic acids

Abstract

. Can. J. Chem. 66, 1695 (1988). The synthesis of a series of n-dodecyloligo(oxyethylene) carboxylic acids of general formula ClzH25(OCH2CH2)nOCH2COOH (n = 0 to 5) and application of these compounds for the separation of Zn(lI), Cd(II), and Hg(I1) in extraction are reported. Negligible extractability of the metal ions investigated was found usingdodecyloxyacetic acid (n = 0) which indicated that complexation resulted from metal-cation interaction with oxygen atoms of the polyoxyethylene chain incorporated into the molecule of complexon. In extractions from aqueous solutions containing ZnCl,, CdCI2, HgC12, and NaOH (pH regulator), loading of the organic phases increased for extractants with more oxyethylene units. In particular, Hg(I1) extractability and molecular structure of the extractant are related. The selectivity of extraction increased drastically if NaCl was added to the initial aqueous phase, as the extractabilities of Cd(I1) and, particularly, Hg(1I) declined while the extractability of Zn(I1) remained high. Selectivity of extraction is produced by the complex chemical equilibria resulted from complexation of the metal cation by an alkyloligoether carboxylic acid in the organic phase and by C1-and OH-anions in the aqueous phase. Thus, aqueous solution parameters greatly influence the efficiency and the selectivity of the extraction process and suitable experimental conditions are very important.JERZY STRZELBICKI, WITOLD CHAREWICZ, JORG BEGER, et LUTZ HINZ. Can. J. Chem. 66, 1695 (1988). On a rCalisC la synthttse d'une sCrie d'acides n-dodCcyloligo(oxyCthyl~ne)carboxyliques de formule gCnCrale ClzH25(OCH2CH2),OCH2C0OH (n = 0 a 5) et on a examink I'utilitC de ces composCs pour sCparer et extraire les ions Zn(II), Cd(l1) et Hg(I1). La quantitC d'ions mktalliques extraite par I'acide dodCcyloxyacCtique (n = 0) est nkgligeable; ce rCsultat indique que la complexation est diie aux interactions des ions mktalliques avec les atomes d'oxyghe de la chaine polyoxyCthylttne incorporCe dans la molCcule complexante. Lors d'extractions effectuCes a partir de solutions aqueuses contenant du ZnC12, du CdC12, du HgC12 et du NaOH (pour rCgulariser le pH), les molCcules complexantes contenant le plus grand nombre dlunitCs oxymCthyl6nes provoquent une augmentation de la concentration des ions extraits dans les phases organiques; on a pu mettre en Cvidence une relation entre la facilitC d'extraction du Hg(I1) et la structure molCculaire des molCcules complexantes. La sClectivitC des extractions augmente d'une f a~o n drastique lorsqu'on ajoute du NaCl h la phase aqueuse initiale; dans ces conditions, la facilitC d'extraction du Cd(I1) et, en particulier, celle du Hg(I1) diminuent alors que celle du Zn(I1) demeure ClevCe. La sClectivitC des extractions est le reflet d'Cquilibres chimiques complexes qui proviennent de la complexation des cations mitalliques par un acide alkyloligoCther carboxylique dans la phase organique et par les anions C1-et OH-dans la phase aqueuse. Ainsi, les paramtttres de la solution aqueuse influence...