Water pollution, especially caused due to the indiscriminate release of heavy metals as a result of anthropogenic activities is a major concern worldwide. Chromium, a heavy metal, regardless of its commercial importance has found to be a potent water pollutant. Chromium generally exist as hexavalent (Cr(VI)) and trivalent (Cr(III)) chromium in the environment. Cr(VI) is ascertained to be more toxic compared to Cr(III) and the former is identified as a carcinogen by the World Health Organisation (WHO). Some of the conventional methods currently available for chromium pollution mitigation are not cost effective and most importantly lead to secondary pollution in the form of sludge. Bioremediation is a promising alternative technique which is also ecofriendly. The bioremediation process utilises biological materials such as microorganisms and agricultural byproducts. Biosorption is a bioremediation process that is a surface related phenomenon involving adsorption of contaminant chromium ions onto the binding sites of the biosorbents. In addition to the efforts made to the remediation of chromium, continuous monitoring of chromium contaminant level in polluted water bodies becomes imperative. The present research study encompasses findings related to bioremediation and detection of chromium ions using bacterial cells. The first part of the dissertation involves studies pertaining to the bioremediation of chromium ions using different bacterial strains as biosorbent. For the study, bacterial strains procured from a microbial culture collection bank as well as those isolated from chromium polluted water samples collected from an industrial site were assessed for their ability to remediate chromium. The next aim of the study was to elucidate the mechanisms involved in the bioremediation of chromium ions by the bacterial cells for which the different characterisation methods such as, Fourier Transform Infrared (FTIR) spectroscopy, Energy Dispersive Spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and zeta potential measurements which enabled to throw light on the reactions occurring at the bacterial cell surface-chromium solution interface. The later part of the study examines the capability of the bacterial strains used in the bioremediation studies as sensors for the detection of Cr(VI) and Cr(III) ions by adopting electroanalytical techniques, such as, Cyclic Voltammetry (CV) and Cathodic Stripping Voltammetry (CSV), wherein a microbe-modified Carbon Paste Electrode (CPE) was used as the working electrode in a typical three electrode electrochemical cell with Saturated Calomel Electrode (SCE) and platinum wire used as the reference and auxiliary electrodes respectively. The key objectives of the present study are as follows: (i) To study the bioremediation of Cr(VI) and Cr(III) ions present in aqueous solutions using two bacterial strains procured from a microbial culture collection bank as biosorbents. The bacterial strains used were Corynebacterium paurometabolum (Cp), a Gram positive bacterium and Citrobacter freundii (Cf), a Gram negative bacterium. The various factors affecting the biosorption process are to be investigated. (ii) To isolate and identify bacterial strains from water samples collected from chromium contaminated mining site in Sukinda, Odisha, India, by adopting appropriate microbiological and molecular biological procedures. (iii) To study the various factors affecting bioremediation of Cr(VI) using the mine isolates (Chromobacterium sp. (Cb) and Sphingopyxis sp. (Sp)) both Gram negative, as biosorbents. (iv) To elucidate the mechanisms adopted by the chosen bacterial cells in the bioremediation of chromium. (v) To develop an electrochemical-microbial sensor by modifying the Carbon Paste Electrode (CPE) using the bacterial strains for the detection of Cr(VI) and Cr(III) ions present in aqueous solutions. (vi) To determine the capability of the developed sensor in the detection of Cr ions in mine water samples collected from Sukinda chromite mine in Odisha, India. (vii) To elucidate the mechanisms occurring at the bio-modified electrode–solution interface. A compendious description of the findings from the present work is given below: The capability of two bacterial strains procured from a microbial culture collection bank (MTCC), Corynebacterium paurometabolum (Gram positive bacterium) and Citrobacter freundii (Gram negative bacterium) as biosorbents for Cr (VI) and Cr(III) ions was assessed. Further, it became of interest to translate the studies related to bioremediation to an industrial situation. For this, bacterial strains were isolated from chromium contaminated water samples collected from surface water of Sukinda chromite mine in Odisha, India. Based on detailed microbiological and molecular biological protocols, two strains of bacteria were identified and characterised as Chromobacterium sp. and Sphingopyxis sp. The bioremediation efficiency of the strains was evaluated taking into consideration the various factors such as effect of contact time of bacterial cells with the chromium ions, pH of the chromium ion solution, biomass loading and initial chromium ion concentration. The Cr(VI) biosorption efficiency obtained for C. freundii was found to be about 59 %, followed by Sphingopyxis sp. and C. paurometabolum ≈ Chromobacterium sp. in the range of 50 % to 55 %. Subsequent to interaction of the bacterial cells with the Cr(VI) solution, the residual chromium was found to be in the form of Cr(III) ions. Hence, complete bioremediation of Cr(VI) could be achieved in terms of both biosorption and bioreduction processes using all the bacterial strains. It was found that the bioreduction process occurring in conjunction with the biosorption process resulted in nil concentration of Cr(VI) ions in the bulk solution. Similarly, studies related to bioremediation of Cr(III) using C. paurometabolum and C. freundii bacterial strains were also performed with higher biosorption efficiency achieved for the former, 50 % compared to 30 % obtained for C. freundii bacterial cells. The bioremediation of Cr(III) ions by the bacterial cells is achieved by the biosorption process. Biosorption of Cr ions by all the bacterial strains were found to follow a typical Langmuirian behaviour. The bioremediation process by the bacterial strains was also evaluated using suitable kinetic models and the results indicated that the bioremediation of Cr(VI) and Cr(III) by C. paurometabolum and C. freundii respectively followed pseudo first order kinetics, while the bioremediation of Cr(VI) by C. freundii, Chromobacterium sp. and Sphingopyxis sp. followed pseudo second order kinetics. It becomes of importance to ascertain the mechanisms of bioremediation of chromium ions by the bacterial cells and for this, different characterisation methods were adopted that helped in deducing the reactions occurring at the bacterial cell surface-chromium solution interface. The involvement of chemical forces in the bioremediation process was corroborated by the achievement of only partial desorption of chromium ions from the biosorbed bacterial cells. This was further confirmed by the Gibbs free energy (∆G) values, which were found to be in the range of -25 to -30 kJ/mol. FTIR spectral studies provided evidence in support of the key functional groups present on the bacterial cell surface such as, –OH, -COOH and –NH, which facilitated the binding with chromium. The EDS data for chromium biosorbed bacterial cells showed peaks corresponding to chromium, thereby confirming the binding of chromium by the bacterial cells. The redox state of chromium bound on the bacterial cell surface was determined with the help of XPS analysis. In the Cr2p XPS spectra obtained for the bacterial cells interacted with Cr(VI), it was interesting to observe a peak corresponding to Cr(III) in addition to Cr(VI), unequivocally indicating that the Cr(III) formed via bioreduction was not only released into the bulk solution but also got biosorbed on the bacterial cell surface. Apparent shifts in the binding energy values for the bacterial cells interacted with chromium were observed in the spectra recorded corresponding to C1s, O1s, N1s, P2p and S2p as compared to the spectra obtained for the bacterial cells alone. This attests to the fact that the functional groups corresponding to the elements mentioned are involved in chemical interaction with the chromium ions or are involved in the donation of electrons to bring about reduction of Cr(VI) to the less toxic Cr(III). The variation in the charge of the bacterial cell surface before and after interaction with chromium ions was monitored by performing zeta potential measurements as a function of pH. The surface charge of the bacterial cells alone was found to be negative over a wide range of pH. Subsequent to interaction of the bacterial cells with the negatively charged oxyanions of Cr(VI) ions, the surface charge was observed to be less electronegative, which further confirmed the binding of the positively charged Cr(III) ions formed via bioreduction on the bacterial cell surface. Similar results were also observed in the case when cells were allowed to interact with Cr(III) ions. The shifts in the iso-electric point for bacterial cells interacted with chromium ions further testified to the involvement of chemical binding forces in the bioremediation process. The findings obtained from the different characterisation methods enabled in understanding the reactions that are occurring at the bacterial cell surface-Cr solution interface. Initially, biosorption via electrostatic interaction of negatively charged oxyanions of Cr(VI) with the positively charged amino groups present on the bacterial cell surface takes place. Subsequent to the biosorption of Cr(VI) ions, the adjacent electron donating functional groups containing ligands present on the bacterial cell surface reduce Cr(VI) to Cr(III) via the reactions shown below: Bioreduction involving –OH group Bioreduction involving –SH group It can be seen that, the reactions involving bioreduction of Cr(VI) in the form of chromate oxyanion to Cr(III) involving hydroxyl and thiol group present on the bacterial cell surface result in the formation of intermediates, chromate-oxy and chromate-thio ester respectively. These intermediates facilitate the transfer of electrons from oxygen/sulphur donor centers to Cr(VI) acceptor molecule, thereby resulting in the reduction of Cr(VI) to Cr(III). The Cr(III) ions thus formed are then either released into the bulk solution or get complexed with the binding groups present on the bacterial cell surface. The next objective was to explore the potential of bacterial strains as sensors for the detection of Cr(VI) and Cr(III) ions. The chromium ions were detected using CV and CSV, both of which are electroanalytical techniques. For this, CPE was coated with the bacterial strains, C. paurometabolum, C. freundii, Chromobacterium sp. and Sphingopyxis sp., and the modified electrode was used as the working electrode in a typical three electrode electrochemical cell. These biosensors developed using each of the aforementioned strains resulted in a ~ 2 to 2.5 fold improved performance compared to the bare CPE for the detection of Cr(VI) ions, due to the binding ability of the various functional groups present on the bacterial cell surface. The lower limit of detection (LLOD) obtained for Cr(VI) and Cr(III) ions using CV technique was found to be 1x10-4 M and 5x10-4 M respectively. The LLOD was further improved to 1x10-9 M and 1x10-7 M for Cr(VI) and Cr(III) respectively using CSV. From the voltammograms obtained, it was postulated that the different functional groups present on the bacterial cell surface facilitate the detection of the chromium ions. Additionally, the developed microbial sensors were also found to be capable of detecting Cr(VI) ions in mine water samples collected from Sukinda chromite mine Odisha, India. In summary, the mechanisms of bioremediation of toxic Cr(VI) ions have been delineated as comprising of both biosorption and bioreduction processes. The residual Cr(VI) concentration subsequent to the treatment of the Cr(VI) aqueous solution with the bacterial cells was found to be nil, which meets the regulatory limit of 0.05 mg L-1 put forward by the US-Environmental Protection Agency (EPA) for a safe effluent discharge. Moreover, it has also been demonstrated that the chosen bacterial strains could be used as sensors for the detection of upto nanomolar concentration of Cr(VI) ions, under optimum conditions.

Binuclear mixed biscarbene complexes of bithiophene were synthesized via the classical Fischer method of synthesis. The metal carbonyls, Mo(CO)6, Cr(CO)6, W(CO)6 and Mn(MeCp)(CO)3 were reacted with dilithiated bithiophene to afford complexes of the formula, [M(CO)5{C(OEt)C4H2S-C4H2SC(OEt})M'(CO)5] (in case of manganese, M(CO)5 is replaced with MMeCp(CO)2), where [M] and [M'] are the metal carbonyls in different combinations. Quenching was achieved with triethyl oxonium tetrafluoroborate. In all the reactions the products included monocarbene complexes, biscarbene complexes and the decomposition products. C-C coupling reactions produced unexpected biscarbene complexes of Cr, W, and Mo having extended bithiophene spacers. The complexes were of the formula, [M(CO)5{C(OEt)C4H2S-C4H2SC(R)-C(R)C4H2S-C4H2SC(OEt})M'(CO)5] (R = O, OH or OEt). These complexes were characterized with NMR, infrared spectroscopy and some with mass spectrometry. Furthermore, three biscarbene complexes of the metal combinations Mo(CO)6 and Cr(CO)6, W(CO)6 and Cr(CO)6, and Mn(MeCp)(CO)3 and Cr(CO)6 were all reacted with 3-hexyne. The result was the benzannulation or the Dötz products. / Chemistry / M. Sc. (Chemistry)

De par leurs propriétés mécaniques et anti-corrosion élevées, les revêtements métalliques de chrome sont utilisés dans de nombreux domaines tels que l’aéronautique, l’automobile, le ferroviaire, la défense,… Aujourd’hui le chromage dur industriel, réalisé à partir de chrome hexavalent, est fortement menacé par la directive européenne REACH qui prévoit l’interdiction d’utilisation de sels de chrome VI (classé CMR) à l’horizon 2017. Dans ce contexte le projet HCTC (Hard Chromium by Trivalent Chromium) regroupe 16 partenaires industriels et 2 partenaires académiques sous la coordination de l’Institut de Recherche Technologique Matériaux, Métallurgie, Procédés (IRT M2P) afin de développer une alternative à base de sel de chrome trivalent. Le développement d’un procédé de substitution à partir de sels de chrome trivalent nécessite de répondre aux interrogations liées notamment à la difficulté de réduire les ions Cr3+ formant en solution aqueuse un complexe hexa-aqua [Cr(H2O)6]3+ très stable et difficilement réductible. Afin de faciliter la réduction, l’ensemble des travaux recensés dans la littérature prône l’utilisation d’un agent complexant organique afin d’augmenter l’accessibilité du chrome. Une première partie de ce travail de thèse a été de caractériser les dépôts de chrome métallique réalisés à partir de la formulation de chrome III (EXDBA 1318) afin de mettre en évidence l’influence des paramètres de chromage (température du bain de traitement, densité de courant,…) sur les propriétés physico-chimiques des dépôts (Morphologie, cristallinité, composition chimique). Les résultats ont montré que la diminution de fissures tranversantes est généralement accompagnée d’une augmentation du taux de carbure de chrome qui dégrade l’état cristallin. La compréhension et l’optimisation du procédé a permis la réalisation de dépôts avec des propriétés physico-chimiques permettant de lancer les premiers essaies industriels dont les premiers retours sont très encourageants pour certaines applications (essentiellement automobile).Dans une deuxième partie plus fondamentale, des analyses par HPLC-ICP/AES ont mis en évidence la complexation du chrome par différents agents complexant. Les résultats obtenus ont montré que la complexation étaient d’autant plus importante que le pH est haut (pH=5) et le rapport molaire [Cr]/[Cplx] faible (1/10). Les mécanismes de réduction associés aux taux de complexation ont ensuite été déterminés par des mesures de voltammétrie cyclique en utilisant des électrodes sérigraphiées modifiées par de l’or. Les voltammogrammes obtenus montrent que la complexation du chrome par un agent complexant permet de passer d’un mécanisme de réduction en deux étape (Cr3+  Cr2+  Cr) en une seule (Cr3+  Cr).Une dernière partie du travail a été de définir l’influence de la chimie sur bain (pH et rapport molaire [Cr]/[Cplx]) sur les propriétés physico-chimiques des dépôts. Les résultats obtenus ont montré que pour des solutions faiblement complexées il est préférable de travailler à des pH bas et d’appliquer de faibles densités de courant (<15A/dm²) tandis qu’une augmentation du taux de complexation du chrome par l’agent complexant nécessite d’appliquer des densités de courant plus fortes. Ce travail a aussi permis de montrer l’existence d’une zone de pH optimale pour un rapport molaire [Cr]/[Cplx] donnée. L’existence de cette zone de pH révèle l’existence d’un domaine d’équilibre en solution, favorable à la réduction du chrome. L’ensemble de ces travaux plus fondamentaux ont permis d’améliorer les connaissances sur le procédé de chromage à partir d’un sel de chrome trivalent et ainsi de réfléchir à une nouvelle formulation pour des applications plus critiques où la solution actuelle a pu montrer quelques limites. / Due to their high mechanical and anti-corrosion properties, chromium metal coatings are used in many fields such as aeronautics, automotive, railway, defense, etc. Today industrial hard chromium coating, made from of hexavalent chromium, is strongly threatened by the European REACH Directive, which provides for the prohibition of the use of chromium VI salts (classified as CMR) by 2017. In this context, the HCTC project (Hard Chromium by Trivalent Chromium) groups together 16 industrial partners and 2 academic partners under the coordination of the Institute for Materials, Metallurgy and Process Technology Research (IRT M2P) to develop an alternative based on trivalent chromium salt. The development of a substitution process from trivalent chromium salts requires answering the questions related in particular to the difficulty of reducing the Cr3+ ions forming in aqueous solution a very stable hexa-aqua [Cr(H2O)6]3+ complex and hardly reducible. In order to facilitate the reduction, all the works listed in the literature advocate the use of an organic complexing agent in order to increase the accessibility of chromium.A first part of this thesis work was to characterize the chromium metal deposits made from the chromium III formulation (EXDBA 1318) in order to highlight the influence of chromium parameters (bath temperature, density of current, ...) on physico-chemicals properties of the deposits (Morphology, crystallinity, chemical composition). The results showed that the decrease of transverse cracks is generally accompanied by an increase in chromium carbide which degrades the crystalline state. The understanding and the optimization of the process allowed the realization of deposits with physico-chemical properties allowing to launch the first industrial tests whose first returns are very encouraging for certain applications (mainly automobile).In a second, more fundamental part, HPLC-ICP / AES analyzes have demonstrated the complexation of chromium by different complexing agents. The results obtained showed that the complexation was all the more important that the pH is high (pH = 5) and the molar ratio [Cr] / [Cplx] low (1/10). Reduction mechanisms associated with complexation rates were then determined by cyclic voltammetry measurements using gold-modified screen-printed electrodes. The voltammograms obtained show that the complexation of chromium by a complexing agent makes it possible to go from a reduction mechanism in two steps (Cr3+  Cr2+  Cr) to a single one (Cr3+  Cr).A final part of the work was to define the influence of bath chemistry (pH and [Cr]/[Cplx] molar ratio) on the physico-chemical properties of coatings. The results obtained showed that for weakly complexed solutions it is preferable to work at low pH and to apply low current densities (<15A / dm²) while an increase in the chromium complexation rate by the complexing agent requires the application of higher current densities. This work also showed the existence of an optimal pH zone for a given [Cr]/[Cplx] molar ratio. The existence of this zone of pH reveals the existence of a balance domain in solution, favorable to the reduction of chromium. All of these more fundamental works have made it possible to improve the knowledge on the chromium plating process from a trivalent chromium salt and thus to think about a new formulation for more critical applications where the current solution has been able to show some limits.

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M.Sc. / The aim of this study is to show that there exists a parallelism between the effect of the concentration of the itinerant electrons per atoom, and the applied hydrostatic pressure, p, on the magnetic phase diagram of a Cr + 0.2 at.% Ir alloy. This Cr-Ir alloy was chosen, because it contains all possible magnetic phases that can exist in a Cr alloy.

M.Sc. / Impurity resonance scattering effects are investigated in the Cr-Ga alloy system. This system has a triple point on its magnetic phase diagram where the paramagnetic (P), incommensurate (I) and commensurate (C) spin-density-wave (SDW) states co-exist. Alloying Cr with the nonmagnetic nontransitional element Ga affects the magnetic properties of Cr in a very unique way. In order to investigate the presence of resonant impurity scattering effects in binary Cr-Ga alloys, electrical resistivity measurements were carried out in the temperature range between 6 K and 85 K. The results of the investigation show: • A nonmonotonic increase in the residual resistivity of the Cr-Ga system with an increase in the Ga content, due to the presence of resonant impurity scattering of conduction electrons. • A low-temperature resistivity minimum observed in some of the Cr-Ga alloys, taken as further evidence for the presence of resonant impurity scattering effects on the conduction electrons. The impurity resonance scattering effects on the electrical resistivity of a Cr + 1.2 at.% Ga alloy, doped with V and Mn to tune the Fermi level through the impurity level, are also investigated. The investigation was complemented by thermal expansion and velocity of sound measurements in the temperature range 77 K to 450 K for the Cr + 1.2 at.% Ga alloy only. This specific Ga concentration was chosen to allow for studying resonant scattering effects in both the ISDW and CSDW phases of the system. This is possible because concentration of 1.2 at.% Ga is just above the triple point concentration. Doping with Mn to increase the electron concentration (eA) drives the alloy deeper into the CSDW phase region of the phase diagram, while doping with V, on the other hand, will drive the alloy towards the ISDW phase region. The results of the study are summarized as follows: • Two relatively sharp peaks, attributed to resonant impurity scattering effects, are observed in the curve of the residual resisitivity as a function of dopant concentration in the ISDW phase of the ternary (Cr0.988Ga0.012)1-xVx and (Cr0.988Ga0.012)1-yMny alloy systems. v • At 0 K the (Cr0.988Ga0.012)1-yMny alloy system transforms from the ISDW to the CSDW phase at y ≅ 0.0032, giving a CSDW phase for y > 0.0032. A peak is observed in the residual resistivity at about this Mn content. This peak can then either be ascribed to a jump occurring in the residual resistivity when the CSDW phase is entered from the ISDW phase or to resonant scattering effects. The conclusion is that the peak is rather related to the latter effect. • The resistivity as a function of temperature of the above two ternary alloy series show well-developed or weak minima at low temperatures for some of the samples. This is taken as further evidence of the influence of impurity resonant scattering effects on the resistivity of these alloys. • The resistivity and thermal expansion coefficient of the polycrystalline Cr0.988Ga0.012 alloy of the present study behaves anomalously close to the ISDW-CSDW phase transition temperature and warrant further investigation. The concentration-temperature magnetic phase diagram of the (Cr0.988Ga0.012)(Mn,V) alloy system was constructed from the magnetic transition temperatures obtained from electrical resistivity measurements. Theoretical analysis of the phase diagram was done using the two-band imperfect nesting model of Machida and Fujita. The results show: • A triple point at (0.21 at.% V, 225 K) where the ISDW, CSDW and P phases coexist on the magnetic phase diagram. • The curvature of all three theoretically calculated phase transition lines in the region of the triple point is of the same sign as that observed experimentally. • The theoretical fit is very good for the ISDW-P and ISDW-CSDW phase transition boundaries, while there is some discrepancy for the CSDW-P phase transition line. This may be attributed to the fact that the theory is one dimensional and that it does not include electron-hole pair breaking effects due to impurity scattering and also not effects of changes in the density of states due to alloying. / Dr. A.R.E Prinsloo Prof. H.L. Alberts

M.Sc. / In search of developing new pyrazolyl complexes that can be used for ethylene transformation reactions, bis(pyrazolyl)alky carbonyl and amine complexes were prepared. The reaction between 3,5-dimethylpyrazole with alkyl-carbonyl chloride linkers in the presence of triethylamine as a base produced the ligands, 1,3-bis(3,5- dimethylpyrazol-1-yl)-propan-1-one (L1), 1,2-bis(3,5-dimethylpyrazol-1-yl)-ethane- 1,2-dione (L2), 1,4-bis(3,5-dimethylpyrazol-1-yl)-butane-1,4-dione (L3) and 1,6- bis(3,5-dimethylpyrazol-1-yl)-hexane-1,6-dione (L4) as white to brown crystalline solids in good yields. Ligand L5 was prepared by using bis(2-chloroethyl)-amine hydrochloride and 3,5- dimethylpyrazolevia via a phase-transfer reaction, while L6 was obtained using the bis(2-chloroethyl)-amine hydrochloride and 3,5-diphenypyrazole in the presence of triethylamine as a base. They were isolated in moderate yields, while their ditertiarypyrazole derivative was not obtained at all. All the ligands were characterized by a combination of 1H and 13C{1H}-NMR spectroscopy, infrared spectroscopy, elemental analysis and mass spectrometry. Ligands L1 and L4 were further confirmed by X-ray crystallography. Ligands L1 and L6 were subsequently used to prepare their corresponding Pd, Ni and Cr complexes. L1 was reacted with [PdCl2(NCMe)2] to form a bidentate complex 1,3- bis-(3,5-dimethylpyrazol-1-yl)-propan-1-one palladium dichloride (1a) when the reaction was heated at 80 oC, while a tridentate complex 1,3-bis(3,5-dimethylpyrazol- 1-yl)-propan-1-one palladium chloride (1b) was obtained when the reaction was refluxed. 1,3-bis(3,5-dimethylpyrazol-1-yl)-propan-1-one nickel(II) bromide (2) was obtained when NiBr2 was reacted with L1 at room temperature while the reaction between L1 and [CrCl3(THF)3] gave 1,3-bis(3,5-dimethylpyrazol-1-yl)-propan-1-one chromium(III) chloride (3). Ligand L6 was reacted with the same metal salts to give bis[2-(3,5-dimethylpyrazol- 1-yl)-ethyl] amine palladium(II) chloride (4), bis[2-(3,5-dimethylpyrazol-1-yl)-ethyl] amine nickel(II) chloride (5) and bis[2-(3,5-dimethylpyrazol-1-yl)-ethyl] amine chromium(III) chloride (6). All the complexes were characterized by the already mentioned characterization techniques and X-ray analysis was performed for 1b and 4. Ethylene transformation reactions were performed with complexes 1a, 2, 3, 5 and 6, and complexes 1a and 4 were not used because of their geometrical structures, which prevented them to be active for such reactions. Using MMAO and EtAlCl2 as cocatalysts complexes 1a and 3 showed no activity, however complexes 2 and 6 were active. Complex 2 was used with MMAO and showed no activity, while with EtAlCl2 oligomers were produced. Gas-chromatography analysis of the products showed that C6-C14+ oligomers were obtained. Temperature variation reactions performed under standard conditions of 20 bar ethylene pressure and 200 equivalents of EtAlCl2 in one hour showed that certain oligomers were not favoured under certain temperatures. Ethylene reactions with complex 6 and EtAlCl2 did not form any product but with MMAO polymer material was obtained. Analysis of the polymer by differential scanning calometry proved that the product was high density polyethylene. Studies of temperature, co-catalyst and pressure variations were performed. As expected for temperature studies the catalyst decomposed at high temperatures (above 40 oC), while for co-catalyst studies 3000 equivalents of MMAO gave the lowest TON. Pressure variations studies showed that an increase in ethylene pressure also increased the TON, but above 30 bar the activity became stable.

Chromium exists largely in two oxidation states, namely hexavalent chromium (Cr(VI)) which is carcinogenic, mutagenic to living organisms including humans and trivalent chromium (Cr(III)) which is known to be 1000 times less toxic than Cr(VI). It is therefore desirable in most cases to reduce Cr(VI) to Cr(III). Various studies have been conducted on the Cr(VI) reduction process either in situ or ex situ. However in situ bioremediation using permeable reactive barrier system appears as a potential and attractive technology compared to other in situ technologies. This study was conducted to evaluate the reduction of Cr(VI) to Cr(III) in the short term and regeneration of the biological reactive barrier to achieve continuous long term operation. It was observed from the study that the chromium hydroxide Cr(OH)3(s) precipitated and thus affected the porosity and hydraulic conductivity of the barrier system. It was therefore proposed to implement a regeneration process involving remobilization of precipitated Cr(OH)3 using a dilute acid (0.1% HCl) and recover Cr(III) by electrokinetics. Lowering the pH in the reactor introduced harsh conditions which necessitated the evaluation of a possible culture shift during the regeneration phase. Microbial culture composition during bioremediation and after soil washing was evaluated using a 16S rRNA finger printing method. The microbial barrier was initially inoculated with indigenous bacterial species from dried sludge. The results presented in the phylogenic tree diagrams confirm that, after microbial barrier system operation, the well-known Cr(VI) reducers Bacillus mycoides, Lysinibacillus fusiformis and Micrococcus lylae were the predominant species in the microbial community of the barrier. The microbial barrier system successfully achieved near complete removal of Cr(VI), whereby approximately 75% Cr(VI) removal was achieved within 63 days of operation. The formation of Cr(OH)3(s) was observed in the second week of operation. After 4 weeks of operating the mesocosm under soil washing with 0.1% HCl and electrokinetics remediation with a DC voltage of 50-150 V an increase in total chromium (73%) was observed suggesting that the trapped chromium species in the mesocosm was effectively remobilized with the assumption that Cr(III) had attached to the cathode forming a white-yellow precipitate layer around the cathode. Additionally more than 95% Cr(VI) was transformed to lower toxicity Cr(III) during electrokinetics and soil washing remediation. However, one of the limitations of electrokinetics is near anode focusing effect whereby a layer of precipitate is formed around the anode that lead to the reduction of efficiency of the technology. / Dissertation (MSc)--University of Pretoria, 2014. / lk2014 / Chemical Engineering / MSc / Unrestricted

An innovative sampling technique employing extractant impregnated membranes is presented for the selective sorption and stabilization of specific oxidation states of chromium. Polymer-based selective ion traps employing the extractants tricaprylmethylammonium chloride (Aliquat-336) and di-(2-ethylhexyl) phosphoric acid (DEHPA) were used for the selective removal and enrichment of the anionic forms of Cr(VI) and cationic forms of Cr(III), respectively. Results show Aliquat-336 and DEHPA effectively remove Cr(VI) and Cr(III) from aqueous solutions. Extraction efficiency is independent of source concentration from 1-50 ppm but is dependent upon time, pH of the source, ionic strength, extractant concentration, composition of source phase, and choice of stripping agent and stripping agent concentration. Optimum conditions for Cr(VI) and Cr(III) were determined to be 1 v/v% Aliquat-336 and 30 v/v% DEHPA; an extraction time of at least 3-5 days; source phase pH between 3-5; and 1 M NaOH/ 0.5 M HNO3 as stripping agent for Cr(VI) and Cr(III) species, respectively. Batch extraction efficiencies of 97 +/- 3 % were obtained for the optimal conditions. Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) was used for total chromium determination. UV-VIS spectrometry was used for Cr(VI) determination. Scanning Electron Microscopy revealed the physical structure of the polymeric supports and subsequent impregnation was evidenced by the SEM images. X-ray photoelectron spectroscopic results provided the elemental composition of the Versapor-450 membrane to be 71. 5% C, 7.0% O, 9.5% Cl and 12.0% N. The Whatman PP membrane was and 100.0 % C. Elemental composition of 1 v/v% Aliquat-336 on Versapor-450 and Whatman PP membrane was 92.3% C, 0.8% O, 3.6% N, and 3.3% Cl and 94.3% C, 3.3% N, and 2.4% Cl, respectively. Elemental composition of 30 v/v% DEHPA on Versapor-450 and Whatman PP membranes were 78.8% C, 3.4% P, 17.8% O and 76.3% C, 19.3% O, 4.4% P, respectively. Column studies under simulated groundwater conditions utilizing the extractant impregnated membranes showed no statistical difference in Cr(VI) recoveries from those obtained in batch experiments. Cr(III) extraction revealed a statistical difference in analyte recovery vs. batch experiments. This is attributed to the lowered pH and cationic interferences present in simulated groundwater. / Ph. D.