Transport and extraction of Au(lll) using thiourea ligands

Mebrahtu, Fanuel M. (2004-12)

Thesis (MSc)--Stellenbosch University, 2004.

Thesis

ENGLISH ABSTRACT: A series of di- and mono-substituted acyl(aroyl) thioureas were examined for the extraction and transportation of Au(III). Two-phase metal ion extraction experiments were employed to investigate the extraction behaviour of these ligands. The effect of varying ligand concentration on the extraction trend of these ligands was investigated. The results show that the different substituent groups on the benzoyl ring can affect the extraction pattern of the metal. Furthermore, the alkyl substituents on the thiourea moiety and varying the ligand concentration have an influence on the percentage of metal ion extracted. With the exception of the H2L2(N,N-di-propyl-N'- benzoylthiourea ) ligand the di-alkyl substituted thioureas were more efficient for the metal ion extraction than the mono-alkyl ligands. In almost all the experimental set ups there was reduction of the Au(lIl) to Au(l) and Au(O) but it was more pronounced with HL3 (N,N-di-(2-hydroxyethyl)-N'-benzoylthiourea). Transport experiments were also conducted, the experimental set up for transportation was a concentric type cell involving a 3-phase system - 2 aqueous phases ( source and receiving phase) separated by a chloroform membrane incorporating the ligand. The transport results however only gave a satisfactory result of about 5% of gold transported by the HL1 (N,N-dibutyl-N'-benzoylthiourea). All other ligands attempted resulted in metal ion being present in the organic phase, but no metal ion present in the receiving phase. To help drive the transport of the metal ion to the receiving phase CN-, S203 2- and perchloric acid were incorporated into the receiving phase. The transport results were not enhanced with these substances being present in the aqueous receiving phase. The aqueous source and receiving phases were analyzed by flame atomic absorption spectroscopy (FAAS). Finally the N,N-diethyl-N'-camphanoylthiourea (HL10) ligand and its complex with Au(l) were synthesised. Single crystals of the complex were grown for X-ray crystallography and the crystal and molecular structure of the complex was determined. The complex crystallizes in the monoclinic space group P21. The cell parameters are a = 10.7356(7)A b = 16.3443(11)A c = 10.9268(7)A f3 = 103.1450(10t , and final R-factor of 1.76%. The coordination sphere around Au(l) shows a nearly linear arrangement of sulphur and chloride.

AFRIKAANSE OPSOMMING: In hierdie proefskrif is In aantal mono- en di-gesubstitueerde asiel(ariel) thioureums ondersoek vir die transportasie en ekstraksie van Au(III). Twee-fase metaalioon vloeistof-vloeistof ekstraksie eksperimente is gebruik om die ekstraksie patroon van hierdie ligande te ondersoek. Die effek van verskillende ligand konsentrasies op die ekstraksie neiging van hierdie ligande is ondersoek. Resultate toon dat die verskillende substituente op die benziel ring die ekstraksie patroon van die metaalioon beïnvloed. Verder, is gevind dat die alkiel substituente op die thioureum saam met varierende ligand konsentrasies geensins die metaalioon ekstraksie beïnvloed nie. Met die uitsondering van H2L2 (N,N-dipropiel-N'-benzielthioureum) is die di-alkiel gesubstitueerde ligande meer effektief vir metaalioon ekstraksie in vergelyking met die mono-alkiel ligande. In baie van die eksperimente is In reduksie van Au(llI) na Au(l) en Au(O) gesien en dit is baie duidelik met ligand HL3 (N,N-di(2- hidroksie-etiel)N'-benzielthioureum). Alle waterige fases is ge-analiseer met gebruik van Atoomabsorpsie Spektroskopie (AAS). Transportasie eksperimente is ook uitgevoer met gebruik van In drie-fase selsisteem. Twee waterige fases (bron- en ontvang-fase) is geskei met die chloroform membraan fase wat die ligande bevat. Hierdie eksperimente het net In 5% Au(lll) transportasie getoon met HL1(N,N-dibutiel-N'-benzielthioureum). Daar was geen transportasie van Au(lIl) met enige van die ander ligande. Analise van die twee waterige fases het getoon dat die metaalioon eindelik goed ge-ekstraeer is en is teenwoordig in die membraan fase. Om die transportasie van Au(lIl) aan te spoor, is CN-, s2ol- en perchloorsuur in die ontvang-fase geinkorporeer. Die resultate was geensins beïnvloed nie. N,N-di-etiel-N'-kamfonielthioureum (HL10)ligande en die kompleks daarvan met Au(l) is ook gesintetiseer. Enkel-kristalle van die kompleks is verkry en X-straal kristallografiese analiese is onderneem. Hierdie kompleks kristalliseer in die monokliniese ruimtegroep P21,met a =10.7356(7)Á, b=16.3443(11)Á, c=10.9268(7)Á en ~=103.1450(10t. Die finale R-faktor is 1.76%. Die koordinasie om Au(l) toon In liniêre geometrie met swael en chloor.

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