Ligand Design for the selective removal of metal Ions from industrial streams and wastewater

[摘要] ENGLISH ABSTRACT: This thesis reports the development of new types of solvent extractants for use in the hydrometallurgical recovery of base metals, and addresses the ligand design features which are needed to control the strength, transport efficiency and selectivity of these extractants.The first section of the thesis deals with the synthesis of a new series of monocationic Schiff base ligands. The ligands are fully characterized using 1H and 13C NMR, FT-IR, mass spectrometry and elemental analysis. The extraction and bulk liquid membrane transport abilities of the ligands were evaluated by monitoring the extraction and transport of the metal ions Co(II), Ni(II), Cu(II), Zn(II),Cd(II) and Pb(II) over a 24-hour period. Palmitic acid was included in the organic phase. All ligands showed extraction of Cu(II) and Pb(II) ions, with 2 ligands being more selective towards the extraction of Cu(II) whereas the other 2 ligands extracted more Pb(II).The extraction of Pb(II) is most likely due to a synergistic effect, since palmitic acid was added throughout the organic phase. In the transport studies, only Cu(II) ions were transported. pH-isotherms for both Cu(II) and Pb(II) were also carried out for all ligands. Interestingly Pb(II) is extracted better at lower pH's compared to Cu(II) in two cases. This study shows how these salen-type ligands, when used together with palmitic acid, show transport selectivity for Cu(II), and in the extraction studies, extraction selectivity for Cu(II) and Pb(II). Single crystals of two free ligands and two Cu(II) complexes were obtained and these were refined to acceptable levels. Extensive intramolecular and intermolecular hydrogen bonding is found in the free ligand structures. One Cu(II) complex is similar to that in the literature whilst the other Cu(II) complex is novel, with Cu(II) being four co-ordinate in a structure producing a metallocycle.The second section of this thesis describes the synthesis of several new salicylaldoxime scaffolds as well as the anchoring of substituents onto the Schiff bases in section one making them ditopic ligands. These ligands were fully characterized using 1H and 13C NMR, FT-IR, mass spectrometry and elemental microanalysis. Cu(II) was selectively extracted by all the ditopic ligands showing extraction percentages from 69% to 79%. Cu(II) and Pb(II) metal ions were transported throughout into the receiving phase by these ligands. Cu(II) complexes were synthesized using copper (II) acetate and these were characterized using FTIR and mass spectrometry. These Cu(II) complexes were then used in competitive extraction and transport studies of the anions nitrate, chloride and sulfate. Selective extraction and transport was obtained for nitrate and chloride in agreement with the Hofmeister bias.The third section of this thesis aims to investigate how four different carboxylic acids attach to aSchiff base ligand(2-((E)-(2-(2-((E)-5-tert-butyl-2-hydroxybenzylideneamino)ethylamino)ethylimino)methyl)-4-tert-butylphenol); L1before complexation to the metal ion by using NMRstudies. The extraction of both copper and lead was observed whenpalmitic and salicylic acid was used with the ligand. It was observed that the ligand palmitic acid assembly showed the highest uptake of lead ions above pH=5. An extraction experiment involvingpalmitic acid and Pb(II) only gave34% extraction.This behaviour is consistent with synergistic solvent extraction.

[发布机构] Stellenbosch University