M.Tech. / The efficiency of hydrochloric acid leaching of gold from low grade gold-bearing material has been investigated in the presence of sodium hypochlorite (NaOCl) to produce in situ chlorine gas which is an oxidizing agent able to oxidize gold metal to gold soluble forms: Au+ and Au3+. The effect of concentrations of HCl, NaOCl, and mixtures HCl + NaOCl was sought. An investigation on chlorine species was conducted to predict their stability areas. The reactions involved and their mechanisms were established. Prior to leaching, the feed was subjected to fire assay, Atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), X-ray fluorescence (XRF), and Fourier transform infrared spectroscopy (FTIR) analyses, to quantify the various elements, and to find out the chemical composition and the different mineralogical phases which are present. The main minerals found in the feed were: quartz, pyrite, muscovite-2M1, (M); and clinochlore. The grade was found to be 0.62 g/t. It was found from the hydrochloric acid leaching process that most of metals constituents (iron and potassium) of the feed were leached and consumed all the hydrochloric acid. Therefore, leaching of gold from low grade gold-bearing materials in aqueous chlorine solution is not an effective process for now. Hydrochloric acid leaching of cobalt and copper from four oxidized cobalt-bearing ores was studied in the presence of FeCl2 to produce in situ Fe2+ that is a reducing agent able to reduce Co3+ to Co2+ which is the soluble form of cobalt. The effects of the concentrations of HCl, FeCl2, mixture HCl + FeCl2, leaching time, particle size, and the dissolution kinetics were investigated. Prior to leaching the feeds were characterized with XRD, XRF, FTIR, AAS, Scanning electron microscopy (SEM), and gravimetric analysis. Cobalt contents were found to be between 2.59% and 39.76% in the four ores namely, high Cu ore, high Co ore, low Co ore, and high Co ore with mica. Effect of FeCl2 concentrations in HCl solutions involving 35.06 g; 70.13 g; and 105.18 g corresponding to 0.25 M; 0.5 M; and 0.75 M respectively, were studied and the reactions mechanism established. It was found that an increase in FeCl2 concentration increases the Co dissolution due to the reduction of Co3+ into Co2+ which is soluble. High Co extractions of 99%, 99%, 99%, and 95% were obtained when mixtures 1 M HCl + 105.18 g FeCl2 were used as lixiviants for high Cu ore, high Co ore, low Co ore, and high cobalt ore with mica, respectively. Copper recoveries of 88%, 77%, 75%, and 86% were obtained for high Cu ore, high Co ore, low Co ore, and high Co ore with mica, respectively. The increase in FeCl2 concentration did not have any important effect on the Cu extraction. Mechanisms of involved reactions were established. The order of cobalt leaching reaction was found to be 2 with respect to cobalt concentration. Optimum leaching conditions were found to be: leaching time: 30 minutes, reagent concentrations: mixture 1 M HCl + 105.18 g FeCl2, S/L ratio = 1:20, stirring speed avoiding the vortex, room temperature, pH values from 2.28 to 0.03, and ORP values from 0.402 to 0.322 V.

The problem initially presented was the structural elucidation of a compound obtained when 2,5-dimethylpyrrole was subjected to conditions of acidic reduction. Previous workers had assigned a molecular formula C₁₂H₁₇N to this product and a partial structure had been put forward based on the indolenine system. In the course of this work it was found that the compound obtained by these earlier workers was the result of a reductive self-condensation of 2,5-dimethylpyrrole, and Its structure was conclusively established as 1,3,4,7-tetramethylisoindoline. The methods used in the structural elucidation of this product included elemental analysis of its derivatives, measurement of its basicity and equivalent weight, infrared and ultraviolet spectroscopic evidence, oxidative degradation, and its proton magnetic resonance spectrum. Two related isoindolines were prepared by different routes. 2,4,7-trimethylisoindoline was synthesised by methods analogous to those already known, and the ultraviolet spectrum of its methiodide, when compared with that of the methiodide from 1,3,4,7-tetramethylisoindoline, reinforced the structural assignment of the latter. 1,3-diphenyl-4,7-dimethylisoindoline was obtained by the reductive condensation of acetonylacetone with 2,5-diphenylpyrrole (which did not undergo self-condensation). The favourable result of this reaction suggested that a similar condensation may have occurred to give the 1,3,4,7-tetramethylisoindoline and also admitted the possibility of a general synthesis of substituted isoindolines by this route. An attempt was made to resolve the mechanism of the 2,5-dimethylpyrrole condensation, for which either a Diels-Alder reaction or a ring-opening process may be postulated. The failure of the dimethylpyrrole to show dienic character, even in the presence of very strong dienophiles, together with positive evidence for ring-opening and ketone-pyrrole condensation argued forcibly for the latter mechanism. / Science, Faculty of / Chemistry, Department of / Graduate

M.Sc. / An Acinetobacter sp. strain RFB1 isolated in our laboratory has been shown to have the ability to metabolise inorganic cyanide salts, CO 2, and bicarbonate. The enzyme aggregate responsible for the conversion of these substrates, is located extra-cellularly. Resolution of the extra-cellular complex, a crude enzyme filtrate, was attempted in order to characterise the protein responsible for the reduction of CO 2. The crude enzyme filtrate was separated by means of molecular exclusion chromatography and afforded three fractions with molecular masses ranging from 76 000 to 191 000. Analysis by SDS-electrophoresis, showed that the first protein fraction contained more than ten proteins. Certain of these proteins were identified in the second fraction and other proteins in the third protein fraction. This implies that some denaturation already occurred during molecular exclusion separation. The functionali7ation of CO 2 by protein fractions 1 and 3 supports this argument, and, in addition , cyanide ions were only reduced by fractions 1 and 2. Fatty acids, ranging with chainlengths between C5 and C25, were shown to be present and certain fatty acids were unequivocally identified by GC-mass spectroscopy as the products resulting from CO2 functionali7ation and carbon-carbon bond formation. Ferrous ions, in an optimal concentration of 250 gg cm', were necessary and served as an essential ingredient of the reaction mixture. A rather unusual result was, however, that apart from an initial, relatively small uptake of Fe(II), significant amounts of Fe(III) were not formed and the Fe(II) concentration remained approximately constant during the reaction. This implies that the formed Fe(M) is rapidly reduced to Fe(II) again. Spectroscopic measurements, furthermore, strongly suggested the involvement of an iron-sulphur cluster in a cyclic redox process wherein both Fe(II) and Fe(III) are involved. Carefully conducted experiments pointed to light as the outside source of energy. Qualitative similarities with an artificial photosynthetic process, formulated earlier by J-M. Lehlliii, can be drawn and used partly to explain the experimental results.

(1) In a variety of experimental procedures for Birch reduction at dry-ice temperature (-65 to -78°C), benzamide was reduced to 1,4-dihydrobenzamide: (a) By using Niem’s procedure (27), with lithium and ethanol in liquid ammonia at dry-ice temperature and where ethanol was added slowly after lithium addition, benzamide was reduced to 1,4-dihydrobenzamide., (b) By using Kuehne and Lambert’s method (20), with sodium and ethanol in liquid ammonia at dry-ice temperature, benzamide was reduced to 1,4-dihydrobenzamide., (c) Using Kuehne and Lambert’s method (20), with sodium and ethanol in liquid ammonia at -33°C (the boiling point of NH3), benzamide was reduced to a new compound (possibly 3-cyclohexene-carboxamide) not fully characterized. (2) m-Methoxybenzaminde when subjected to Birch reduction at -78°C or -33°C and with a 3.3 or 8 equivalents of sodium and ethanol by Kuehne and Lambert’s procedure (20), gave the following results: (a) With 3.3 equivalents of sodium and ethanol in liquid ammonia at -78°C, m-methoxybenzamide was reduced to 1,4-dihydro-3-methoxybenzamide.; (b) A reduction similar to (a) with added iron (1 p.p.m.), was done with no noticeably large effects.; (c) Birch reduction of m-methoxybenzamide at -33°C (the boiling point of ammonia), gave a new compound, not identified.; (d) m-Methoxybenzamide, with excess sodium (8 equivalent) at dry-ice temperature, was reduced to a light brownish liquid, not characterized. (3) Terephthalic acid on Birch reduction with lithium and ethanol in liquid ammonia was reduced to a mixture of cis- and trans- 1,4-dihydroterephthalic acid. Cis- and trans- isomers were separated on the basis of difference in solubility, as cis-isomer is more soluble in cold water than trans-isomer.

published_or_final_version / Chemistry / Master / Master of Philosophy

The aim of the work described in this thesis was to develop a more extensive knowledge of the chemistry of neptunium compounds by making rare, air- and moisture sensitive, low formal oxidation state neptunium compounds with full structural and synthetic characterization. The thesis contains three results chapters. Chapter one introduces neptunium chemistry as a background to the results presented. The first review on the molecular non-aqueous neptunium chemistry is provided and the literature reports to date discussed in the context of this. Chapter two describes exploratory synthetic and structural investigations of the organoneptunium complexes supported by the cyclopentadienyl anion, Cp = (C5H5)-, and the (trimethylsilyl)cyclopentadienyl anion, Cp' = (C5H4[Si(CH3)3])-. The syntheses of [Np(Cp)3]n and Np(Cp')3 complexes are detailed and the effect of the trimethylsilyl group of the ligand on the structure and reactivity have been investigated. Complexes were characterized by single crystal X-ray diffractometry, NMR and ATR(IR) spectroscopy. Both organoneptunium complexes were studied in reactions designed to expand the neptunium redox envelope. Notably, the complex Np(Cp')3 is reduced by KC8 in the presence of 2.2.2-cryptand to afford a product assigned as neptunium(II) complex, K(2.2.2-cryptand)[Np(Cp')3] that is thermally very unstable above approx. -10 ºC, in direct analogy to previously reported uranium, thorium and lanthanide complexes of the general formula, K(2.2.2-cryptand)[M(Cp')3]. The reaction between Np(Cp)3Cl and KCp in THF afforded the unanticipated K[NpIII(Cp)4] product as a result of a single-electron reduction presumably arising from Np–C σ-bond homolysis reactivity. This behaviour appears to be unique amongst the actinides for the An(IV)/An(III) redox couple. Chapter three focuses on oxo-bridged homo and heterometallic complexes. The reaction of NpCp3 with dioxygen afforded not only the simple oxide, (μ-O)[An(Cp)3]2, but also a small quantity of the unexpected new trinuclear oxo- neptunium(IV) compound [{(Cp3Np)(μ-O)}2{Np(Cp)2}], which interestingly contains the rare C2v-symetric [An(Cp)2]2+ structural moiety. This oxo-bridged environment is not paralleled in uranium chemistry. The two isostructural oxides, (μ-O)[An(Cp)3]2 (An = U, Np), allow a comparative study of the magnetic exchange phenomena between the two actinide centres demonstrating an exceedingly strong antiferromagnetic coupling, which is largely independent of the communicated Kramers NpIV (5f3, 4I9/2) or non-Kramers UIV (5f2, 3H4) ions. To design heterobimetallic systems, the uranyl(VI) complexes, [(UVIO2)(THF)(H2L)], supported by the calix[4]pyrrole Schiff base macrocycles, H4LOct and H4LEt, were singly-reduced to uranyl(V) with either of the actinide complexes Np(Cp)3 or U(Cp)3, affording isostructural [(Cp3)AnIVOUVO(THF)(H2L)]. Preliminary investigations of the magnetism of the AnIV-O-UV are reported, although their analysis gave counterintuitive results. Chapter four explores the redox chemistry and molecular and electronic structure of neptunium(III) complexes of the doubly deprotonated trans-calix[2]benzene[2]pyrrole, H2(LAr), macrocycle which has a unique π-bonding potential and conformational flexibility. Interestingly, the reactions with neptunium(IV) chloride yielded mono- and dinuclear neptunium(III) complexes, [(LAr)NpCl] and [(LAr)Np2Cl4(THF)3], with a subsequent elimination of the ligand radical; both complexes adopted η6:κ1:η6:κ1 bis(arene) sandwiched structural motif. In a direct analogy to the redox behaviour occurring in the salt metathesis between Np(Cp)3Cl and KCp, the spontaneous reduction derives from the favourable Np(IV)/Np(III) redox system. The reduction of complex [(LAr)NpCl] with NaK3 in DME produces near-black solutions consistent with [NpII(LAr)(DME)] that in the absence of excess NaK3 gradually convert to the metallated (LAr-H)3- neptunium(III) complex, [K(DME)(LAr-H)NpIII(OMe)]2, featuring the actinide centre bound with a ‘metallocene-type’ geometry provided by the two η5-bound pyrrolides of the ligand. The neptunium(III) compounds were characterized in the solid state by single crystal X-ray diffractometry, ATR(IR) spectroscopy and in a solution by NMR and UV-Vis-NIR spectroscopy.

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (M. Phil.)--University of Hong Kong, 1976.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy