Thesis (MScEng) -- Stellenbosch University , 2001. / ENGLISH ABSTRACT: The electrochemical analysis of selected metal ions with the newly biodegradable chelating agents, lminodisuccinic acid (IDS) and Polyaspartic acid (PASP) was performed by cyclic voltammetry using a thin mercury film glassy carbon microelectrode. IDS and PASP are of interest from an environmental perspective. They were introduced as alternatives to chelants and dispersants. The thermodynamic stability constants of these selected metal complexes were determined by cyclic voltammetry (CV). A comparison with similar data obtained using potentiometric methods shows a good correlation between the two methods. This reaffirms that CV is a useful and facile means for evaluating metal-ligand complex thermodynamic data. Furthermore, our results were used to validate the predicted models obtained using an Equilibrium Speciation model JESS program. Capillary Electrophoresis (CE) was used to separate metal-IDS and metal-PASP complexes at different pH's. The separation of these chelates was achieved within 7 minutes. The obtained results were compared with speciation and a reasonable agreement was observed, although the separation ofmetal-PASP showed poor broad peaks. / AFRIKAANSE OPSOMMING: Die elektrochemiese analise van geselekteerde metaal-ione met nuwe biodegredeerbare chelate, Iminodisuksien suur (IDS) en Polyaspartiese suur was gedoen met sikliese voltametrie deur gebruik te maak van 'n dun laag kwik glasagtige koolstof mikroelektrode. Vanaf'n omgewingsstandpunt is IDS en PASP van belang. Hulle was voorgestel as alternatiewe vir chelate en verspreidingsagente. Die termodinamies stabiliteits konstantes van hierdie uitgesoekte metal komplekse was bepaal deur middel van sikliese voltametrie (CV). 'n Vergelyking met soortgelyke data, wat met potensiometriese metodes bepaal was, dui 'n goeie korrelasie aan tussen die twee metodes bepaal was. Dit bevestig die feit dat CV 'n bruikbare en maklike manier is om metal ligand komplekse se termodiniese data te evalueer. Die resultate was ook gebruik om die voorspelde model, wat verkry was deur gebruik te maak van "Equilibrium Speciation model JESS program, te bevestig. Kapillere elektroforese (CE) was gebruik om metal-IDS en metal-PASP komplekse by verskillende pH's te skei. Die skeiding van hierdie chelate was binne sewe minute verkry. Hierdie resultate was vergelyk met die spesiasie data en 'n aanvaarbare ooreenstemming was waargeneem, alhoewel die skeiding van die Metaal-PASP swak pieke toon.

This report chronicles the processes and influences relevant to my work as it has developed over the past three years. I examine how our human separateness and new technologies have effected myself and the work I create, ultimately exploring how technology has aggravated this separation rather than mitigate it. I explain my appropriation of digital, repetitious, and machine-like processes in order to recreate this separation, primarily in the form of drawings, sculptures, and photographs. / text

This dissertation describes a proof-of-principle experiment demonstrating a technique for stable isotope enrichment called Magnetically Activated and Guided Isotope Separation (MAGIS) (1). Over the past century a large number of enriched isotopes have become available, thanks largely to electromagnetic separators called calutrons that were developed during World War II. These isotopes have found applications across an array of fields including medicine, basic science, and energy. Due to substantial maintenance and operating costs, the United States decommissioned the last of its calutrons in 1998, leading to demand for alternative methods of isotope separation. Our experiment suggests the promise for MAGIS as a viable alternative for replenishing stockpiles previously provided by calutrons. Our apparatus combines optical pumping with a scalable magnetic field gradient to enrich lithium-7 (Li-7) by suppressing lithium-6 (Li-6) throughput in a lithium atomic beam. We first evaporate lithium metal in a crucible in order to generate thermal, high flux beam. We then perform optical pumping on Li-6 atoms, magnetically polarizing a substantial fraction of Li-6 atoms into the entirely high-field seeking 2²S₁/₂, F = 1/2 ground state. The resultant beam then samples a magnetic field gradient produced by a 1.5 m long array of rare-earth permanent magnets bent over its length by 20 mrad. This geometry prevents high-field seeking lithium atoms from reaching the plane beyond the magnets, while efficiently deflecting low-field seeking atoms. We measured Li-6 suppression – using independent techniques – along the plane after the magnets beyond a factor of 200, corresponding to Li-7 enrichment to better than 99.95%. As apparatus-specific hindrances appeared to limit this suppression, we believe that we should achieve better enrichment on a commercial apparatus. We also measured both the absolute flux beyond the single, 1.5 in tall magnet array and the efficiency for guiding feedstock material to the collection plane. Given the planar configuration for the field gradient, the flux that we measured should scale linearly with both magnet height and the number of arrays surrounding the source. Our measurements therefore indicate that – at source temperatures that we actually investigated – a commercial apparatus fitting within a volume of just several cubic meters should yield hundreds of grams of enriched (to beyond 99.95%) Li-7 per year. In addition, we observed a competitive ratio between collected material and feedstock with greater than 20% of lithium incident upon the magnet array reaching beyond the magnets. Benchmarking our work against the calutron, we demonstrated comparable enrichment in a manner that should scale to the production of similar quantities. In contrast, however, MAGIS should require vastly less energy input. While calutrons required massive currents for maintaining a static magnetic field over a substantial area, the only non-shared energy expense for MAGIS is the cost for running the low power lasers for optical pumping. Via additional analysis, we have supplemented this proof-of-principle experiment with schemes for applying MAGIS to over half of the stable isotopes in the periodic table. Due to the success of this demonstration and the broad applicability of the principles, we believe that MAGIS will play an important role in the future of stable isotope enrichment. / text

No description available.

The equilibrium and the kinetics of the reaction of Mo (VI) with 8-hydroxyquinoline; 8-hydroxyquinaldine; KELEX 100; LIX63; and LIX65N were studied by solvent extraction. From the equilibrium studies it was concluded that in weakly acidic solution (pH 5 to 6) the overall extraction reaction is (UNFORMATTED TABLE FOLLOWS) MoO₄²⁻ + 2H⁺ + 2HL(o) ↔ (K(ex)) MoO₂L ₂(o) + 2H₂O (TABLE ENDS) where HL is the monoprotic bidentate ligand, "(o)" refers to the organic phase, and K(,ex) is the extraction constant. It was concluded that the complexation reaction requires four protons to convert molybdate into molybdenyl. The extractions constants for LIX63 and 8-hydroxyquinaldine, corrected for the side reaction of the ligand and metal, are 10¹⁶·⁴³ and 10¹⁴·⁴⁰, respectively. In the case of LIX65N, the plot of log(D) vs pH has a maximum at pH 1.0, which was explained qualitatively in terms of protonation of the ligand and molybdic acid at low pH. The extraction constant for the reaction of molybdic acid and the neutral ligand was estimated to be 100,000. The kinetics of extraction Mo (VI) with LIX63, 8-hydroxyquinoline, 8-hydroxyquinaldine, and Kelex 100 were studied in this work. In all cases, except 8-hydroxyquinoline, the rate-determining step of the reaction involves the formation of a 1:1 complex between the neutral ligand and several Mo(VI) species differing in the degree of protonation. The rate-determining step for the reaction of Mo(VI) with 8-hydroxyquinoline involves the formation of a 1:2 complex. The rate constant for the reaction of HMoO₄ with 8-hydroxyquinaldine is four orders of magnitude smaller than the corresponding value reported in the literature for 8-hydroxyquinoline. The slower reaction with 8-hydroxyquinaldine was attributed to the presence of the methyl group next to the nitrogen atom of the ligand which hinders its binding with molybdenum in the rate determining step of the reaction.

Of the interactions utilized in the separation of chemical species, the reversible covalent bond is the strongest and most selective. In order to exploit the selectivity of this interaction, an understanding of the effects of several factors on the formation of the covalent bond have been studied. Covalent chromatography is most useful in solid phase extraction. The strength of the covalent bond will allow for high distribution coefficients needed to quantitatively retain chemical species. The selectivity of the covalent interaction allows for the retention of a specific compound or class of compounds. Under conditions where the covalent bond is no longer formed or will break, a low distribution coefficient is possible, and the compounds may be eluted from the sorbent in a small volume allowing for preconcentration. The sorbent consists of three parts, the active functionality capable of forming reversible covalent bonds, the solid support and the spacer arm that tethers the active functionality to the support. Silica supports demonstrate several advantages over organic supports. However, silica supports have been limited by the activity of the residual silanols and the use of hydrophobic spacer arms. This research describes the preparation and characterization of a modification method for silica with a hydrophilic spacer arm that restricts the sample from the residual silanols. Immobilized phenylboronic acid (PBA) interacts with compounds containing polar functionalities in the correct configuration, but this interaction is dependent on the local environment. Controlling the local environment allows for the control of the interaction provided the effects are understood. Diagnostic chromatography was used to determine the effects of the solvent strength, ionic strength, pH and composition of the mobile phase and the effects of the spacer arm on the interactions of PBA with several compounds. Three phases selective for thiols were also characterized. Thiopyridone attached to mercaptopropyl bonded silica through a disulfide linkage, is used for isolation and detection. Immobilized phenylmercury was utilized for the extraction of thiol containing species while immobilized phenylarsonous acid selectively extracts dithiol compounds. A unique and powerful means of separation of monothiol from dithiol compounds has been demonstrated.

Fundamental solvent extraction studies on the separation of the lanthanides were carried out by investigating both the hydroxamic acid and phosphinic acid reagent families. In general, the lanthanides were found to extract as self-adducts. It was found that the separation of the individual lanthanides with both of these reagent families was adversely affected by steric hindrance.

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