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The oxidation of refractory gold concentrates containing arsenopyrite and pyrite and the simultaneous dissolution of gold in aerated alkaline solutions at ambient temperatures and pressures without the addition of cyanide has been studied. It involves the following aspects: the chemistry of the oxidation of pure arsenopyrite and pyrite minerals in aerated alkaline solutions; the kinetics of oxidation of arsenopyrite and the simultaneous dissolution of gold in such solutions; the kinetics of simultaneous dissolution of gold during the alkaline oxidation of refractory gold concentrates; the electrochemistry of gold in alkaline solutions containing thiosulfate or monothioarsenate; the effect of copper on the leaching of gold in alkaline thiosulfate solutions; and the leaching of gold in alkaline solutions with thioarsenites. The nature and proportions of the products of the oxidation of arsenopyrite in aerated alkaline solutions have been studied using high pressure ion chromatography techniques that have shown that thiosulfate and a new species, monothioarsenate, are the main oxidation products of arsenopyrite apart from arsenate and sulfite. The alkaline oxidation of pyrite primarily yields thiosulfate and sulfite. A kinetic investigation of the oxidation of arsenopyrite with air or oxygen has shown that the initial rate of arsenopyrite oxidation is proportional to the concentration of dissolved oxygen. A reaction mechanism for the oxidation of arsenopyrite has been proposed, which involves an anodic oxidation of the mineral involving hydroxyl ions coupled to a cathodic process for oxygen reduction which is partially controlled by mass transfer of dissolved oxygen to the mineral surface. Detailed studies of the dissolution behaviour of gold in aerated alkaline solutions in the presence of thiosulfate or monothioarsenate by electrochemical and leaching methods have demonstrated that the dissolution rate is very low as compared to that of gold in alkaline cyanide or ammoniacal thiosulfate solutions. It has been found that copper ions catalyze the dissolution of gold in the thiosulfate solutions in the absence of ammonia. The leaching experiments also have shown that gold may dissolve in alkaline thioarsenite solutions, which provides a possible new process option for the leaching of gold. The oxidation of refractory arsenical gold concentrates in aerated alkaline solutions results in the formation of thiosulfate, arsenate and sulfate as well as the dissolution of gold, copper and iron. It appears that the dissolution of gold is due to the complex reactions of gold with thiosulfate ions promoted by the catalytic effect of copper ions. Up to 80% of the gold may be extracted during the oxidation of selected refractory arsenical

Thesis (Ph. D.)--University of Illinois, 1913. / Biographical. "Reprinted from the Physical review, n.s., vol. II., no. 3, September, 1913."

Thesis (Ph. D.)--Princeton University, 1923.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 82-90). Also available in electronic version.

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Magister Scientiae - MSc / Nano-devices are the next step in the application of nanomaterials in modern technology. One area of research that is receiving an increased amount of attention globally is the fabrication of new nano-devices for applications in hydrogen energy technologies. The current work focuses on the synthesis and characterization of nano-devices with potential application in alkaline electrolysis and secondary polymer lithium ion batteries. Previous work with Nickel micro-wires demonstrated the potential to use these nanomaterials as electrodes in alkaline electrolysis. Carbon nanotubes have been shown to posse excellent electrochemical properties. A new direction in research is explored by combining nickel micro-wires with CNT, a new consolidated composite carbon nanocomposite can be realized and the characterization of such a novel composite was the focus of this thesis. Novel composite carbon nanomaterials were synthesized using an electrochemical template technique and a hydrocarbon pyrolysis step. The first step involved the deposition of nickel within the pores of ion track etched Polyethylene terephthalate (PET) membrane; with pore diameters of 1μ, 0.4μ and 0.2 μ. Electrochemical deposition of nickel was carried out galvanostatically in a nickel hard bath between 35-40°C, and using a deposition current density of 75 mAcm2. Carbon nanotubes were then deposited directly onto the surface of the nickel micro-wires via a chemical vapour deposition (CVD) technique using liquid petroleum gas (LPG) as the carbon source. CVD was done at a temperature of 800°C and the deposition time was 5 minutes. The morphology and structural studies of these novel composite nanomaterials were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Electrochemical investigations were done using Cyclic Voltammetry (CV), Chronoamperometry (CA) and Electrochemical Impedance Spectroscopy (EIS). After removal of the template, before CNT CVD growth, SEM images revealed free standing arrays of nickel micro-wires, and after CNT growth via CVD the SEM micrographs showed that the morphology of the Ni micro-wires was moderately altered by the CVD process. From the XRD results it was shown that the crystallinity of the Nimicro-wires was persevered after the CVD process. The XRD of the nickel micro-wires with CNT grown directly on the surface revealed the characteristic CNT peak at 2θ =24.60. Cyclic Voltammetry (CV) was performed on the consolidated composite nanomaterial in an alkaline solution. The CV revealed that the novel composite carbon nanomaterial was the most active for hydrogen evolution when compared to unmodified Ni micro-wires and a flat nickel electrode. This was attributed to the increase in electrochemical accessible surface area. Electrochemical impedance spectroscopy (EIS) showed that the novel composite carbon nanomaterial had a much higher capacitance than the nickel micro-wires, a flat nickel electrode, a flat nickel substrate modified with CNT, and a graphite electrode. When a similar comparison was done using a commercially available anode for lithium ion battery applications, the novel consolidated composite carbon nanomaterial had double the capacitance of the commercial anode. The consolidated composite carbon nanomaterial was modified by depositing Pt on to the surface of the CNT via electroless deposition. The presence of Pt was determined by Energy dispersive spectrometry and the electrocatalytic activity of the Pt modified consolidated composite carbon nanomaterial was significantly improved. The work presented in this thesis provides a new and unique direction in the synthesis and application of novel consolidated carbon nanomaterials through true synergistic effect between nickel micro-wires and CNT. The exploration of the characteristics of the system and the ability to functionalize the CNT with different moieties allows for a wide range of application in energy conversion devices. / South Africa

The development of alkaline phosphatase (AP) has been studied in two species of Urodele amphibian, Ambystoma qracile and Taricha torosa. The enzyme is present in embryo homogenates at gastrulation and increases immensely in activity as development proceeds to the free-swimming stages. The activity level is a product of two isozymic forms that change quantitatively. Using histochemical detection methods, it was possible to correlate the specific activity and electrophoretic data with histological AP development. Some function of AP were related to the available data. A correlation between substrate specificities and function is proposed which may assist in understanding the role of AP in the process of differentiation / Science, Faculty of / Zoology, Department of / Graduate

As atmospheric carbon dioxide (CO2) levels continue to rise due to anthropogenic fossil fuel utilization, the need to develop and employ alternative energy carriers becomes more and more critical. In recent years, interest in hydrogen (H2) has significantly increased as it is a clean and sustainable, alternative fuel, which can be both produced and utilized without greenhouse gas emissions; H2 can be produced via water electrolysis powered by renewable energy sources (RES), such as wind and solar energy, then, H2 can be utilized as a fuel in a hydrogen fuel cell, emitting only water as a by-product. Not only is H2 a clean alternative fuel, but it also provides an economically feasible way of storing renewable energy so that RES supply can be better regulated according to demand. Of the existing water electrolysis technologies, not many offer the ability to produce hydrogen both efficiently and at low cost. The alkaline environment of the more commonly employed traditional alkaline electrolyser allows for the use of non-noble metal electrocatalysts, as well as inexpensive cell materials. This process however suffers from an inefficient cell design. Conversely, the proton exchange membrane water electrolyser (PEMWE) utilizes a solid polymer electrolyte membrane, which allows for a compact, low resistance cell design. However, the harsh acidic environment of this device requires expensive platinum group metal (PGM) catalysts and expensive cell components. Anion exchange membrane water electrolysis (AEMWE) is a promising technology for low-cost, efficient H2 production as it combines the compact cell design of the PEMWE with the favourable alkaline environment of the traditional alkaline electrolyser. The electrochemical water splitting process is limited by the kinetically unfavourable oxygen evolution half-cell reaction (OER), which requires expensive rare catalysts such as iridium, to efficiently carry out the reaction. Nickel (Ni) is a promising inexpensive and abundant catalyst for the OER in alkaline media, due to its high activity and corrosion resistance. A significant increase in OER activity can be achieved by iron (Fe) incorporation into Ni catalysts. The addition of ceria (CeO2), a mixed ionic-electronic conductor with favourable oxygen storage and release properties, can also have a positive effect on catalytic performance. While developing electrocatalysts for improved OER performance is important, evaluating the studied materials as anodes in practical AEMWE devices is imperative as it accounts for the efficiency of the catalysts in electrode layers formed using an anion exchange ionomer (AEI). An AEI is a solid polymer electrolyte that serves as a binder for the particles as well as a hydroxide ion conductor in a catalytic layer of an AEMWE. The main objectives of this thesis are to (i) develop highly active NiFe-based nanoparticle (NP) catalysts with and without CeO2 for the promotion of the OER in AEMWE devices, and (ii) study the effects of commercial AEI type and amount on the efficiency of the produced NiFe-based particles in AEMWE anodes. These objectives will help further understand the behaviour of Ni-based catalysts in AEMWE systems, as well as the effects that catalyst-ionomer interactions can have on anode efficiency in carrying out the OER. The nanoparticles developed in this work were synthesized by an easily scalable chemical reduction method in ethanol using sodium borohydride. Results show that Ni NPs, which are around 4-6 nm in size, with 10 and 20 at% Fe, provide the highest OER performance. Incorporating small amounts of CeO2 into the NiFe materials results in better charge and mass transfer of the catalysts, however it introduces an additional ohmic resistance, which prevails over any OER-promoting interactions between NiFe and CeO2. The best NiFe-based catalysts with and without CeO2 were evaluated as anodes in a single cell AEMWE in combination with the commercial Fumatech Fumion® ionomer as well as the commercial Ionomr Innovations AemionTM ionomer. The single-cell AEMWE analysis of the various catalytic layers shows that Ni90Fe10 with 15 wt% Fumion® shows the best catalytic performance of 1.72 V at 0.8 A cm-2 in 1 M potassium hydroxide (KOH) at 50°C. Ni90Fe10 is also the most stable under operating conditions in comparison to the other tested Ni-based materials. While it was found that using 7 wt% AemionTM provided similar catalytic activity to 15 wt% Fumion®, results show that the AemionTM ionomer interacts with NiFe to inhibit the formation of NiOOH, the OER active phase. The results of this work highlight the complex interactions between Ni-based nanoparticles and anion exchange ionomers towards the OER and provide possible directions for future research and development in high performing Ni-based anodes for AEMWE.

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