On the basis of the difficulty to recognise specific manganese minerals due to their frequent mode of occurrence as fine grained aggregates the present study has been directed towards investigating properties of the minerals which might serve as a readily accessible means of identification. Towards this end attention has been focussed on X-ray diffraction patterns, micro-hardness analysis, a study of various optical properties and differential thermal analysis characteristics. X-ray diffraction patterns using Cr(Ka) radiation have been established for some twenty mineral species and provide the most satisfactory means of recognising the constituents of fine grained mineral intergrowths. The applications and limitations of micro-hardness testing are reviewed and hardness values given for the minerals studied. Attention has been paid to the variation of hardness with applied load and crystal orientation and hardness values given in selected cases. Reflectivity values for white light and for eight wavelengths within the visible spectrum are given for both air and oil. Refractive and absorption indices as determined by the method of Cambon (1949) are quoted, the latter corresponding very well with values determined by classical methods. Differential thermal analysis curves are given for the majority of the minerals, including all the more important forms, and such provide a satisfactory means of distinguishing the main mineral groups.

The lanthanoid sesquioxides exhibit a number of distinct structural phases. Below 2000°C these oxides exist in three crystal systems, namely the A-type hexagonal phase, the B-type monoclinic phase and the C-type cubic phase. With increasing temperature the stability of these structures is generalised by the order C → B → A, although not every oxide will exhibit all phases; this general transition is typical of the middle members of the group. Under ambient conditions, the A phase is preferred for La2O3 to Pm2O3. Both the C and B phases exist for Sm2O3, Eu2O3 and Gd2O3. The C phase is stable at room temperature from Sm2O3 onwards, and at the high atomic number end of the series this phase is preferred. Traditionally, the structures of the heavier sesquioxides (Er2O3 to Lu2O3) have been believed to be cubic from ambient temperature all the way up to their melting points. However, contrary to the current phase diagram, my work has shown that not only are B-type Sm2O3, Eu2O3 and Gd2O3 very stable at ambient temperature, but it is also possible to create 1% monoclinic Yb2O3 by heating and then quenching back to ambient temperature. Of the lanthanoids, praseodymium and terbium are known for their existence in both the +3 and +4 oxidation states. The praseodymium-oxygen system is notable for its multiple stoichiometries. This work presents kinetic data for the phi - beta phase and the sigma - theta phase transitions in this system, the results obtained via high-temperature X-ray powder diffraction and differential scanning calorimetry. The crystal structures of B-type Gd2O3 and Yb2O3 are reported, the former obtained using both laboratory and synchrotron X-ray data and the latter using laboratory data alone. It is proposed that this is the first time these two structures have been determined following the application of temperature alone, without the additional application of pressure.

Nickel extracting industries have been facing challenges reflecting, inter alia, low recoveries of Ni and Co, high acid consumption and inadequate knowledge of dissolution kinetics. In oxic laterite, Ni is mostly associated with goethite. Consequently, for effective extraction of Ni and Co from oxic Ni laterites, a clear understanding of their chemistry, mineralogy and mechanism of sorption in goc;!thite during laterite ore formation is essential. The result from experiment of Ni sorption on goethite revealed that at surface loadings of 0.003 to 0.2 wt. % Ni, only the >Fe(OH)2Ni complex was needed to, fit the data whereas both >Fe(OH)2Ni and (FeOH)2Ni complexes were invoked to fit surface loadings of >0.2 to 0.35 wt. % Ni. At 0.75 wt. % Ni and above, however, the polynuclear complex (FeOH)3Nh was required to fit the data. Similar results were obtained for Co sorption and co-sorption of Ni and Co on goethite. EXAFS results support the existence of Ni surface precipitate or extended polynuclear Ni complex in the Ni-sorbed goethite and Ni laterite. In all the samples, Ni and Co dissolve incongruently with iron. However, there exist disparities in their dissolution and desorption kinetics as a function of aging and concentration, which indicate differences in chemical structure. Modelling of Ni laterite using PHREEQC and equilibrium constants obtained from EQLFOR provides information on the processes of Ni laterite formation and the zones of supergene Ni enrichment as well as prediction of the weathering profile. The solubility product (Ksp) of Ni or Co substituted goethite increases with increasing metal substitution. Similar results were obtained for bi-metal substituted goethite. In general, leaching with dilut~ 2.75 M aqua regia is best for Ni laterites formed at low loading as well as those formed via surface precipitation with Fe content less than 33 wt. % Fe whereas 2.75 M HCI is effective for those formed at high loading containing> 33 wt.% iron.

There is increasing demand for the development of rapid and effective analytical tools to support nuclear forensic investigations of seized suspect materials to determine sample origins and ownership. New methods are sometimes simply adapted from other scientific disciplines and can be effectively used to rapidly prepare complex materials for analysis. The adaptation and re-implementation of such techniques for rapid nuclear forensic characterisation is the focus of this thesis with emphasis on geolocating uranium ore concentrates (UOC) whilst preserving as much of the original sample as possible. A rapid sample solubilisation technique was developed to overcome significant and unpredictable photon self-attenuation observed in U-bearing matrices caused by variable matrix compositions containing dense uranium-bearing particles. The technique enables collection of accurate gamma spectrometric measurements of U-bearing compounds where no photon self-absorption corrections, photon detection efficiency adjustments or sample specific matrix matching are required due to the reproducible and predictable aqueous matrix. The technique was used to prepare and measure 19 UOCs via gamma and alpha spectrometry and the data were statistically analysed by Principal Components Analysis. Half of the UOCs were statistically unique whilst the remaining samples grouped together. The UOCs were re-prepared, re-measured and incorporated into the PCA and plotted in close proximity to the original 3D modelled data. This validates the effectiveness of the procedures to obtain accurate and reliable data and that statistical analysis of the data is able to infer possible sample origins. A second sample preparation technique was developed and tested using U-bearing samples which allows for 1.5 mg of sample to be formed in to a small glass bead after dilution with pure MgSiO3 instead of using a specific flux (usually determined with prior knowledge of sample composition) and could over-dilute the sample and introduce contaminants. The glass was prepared using an iridium-strip resistive fusion device and is produced in less than 10 minutes. The resulting homogeneous flux-free bead of glass was then analysed via laser-ablation ICPMS and the rare earth element (REE) patterns were obtained for reference materials and 9 UOCs. The REEs can be used to infer UOC provenance. The patterns were convincingly similar to chondrite normalised reference values and data from chemically purified UOCs and offer a rapid and effective approach to obtaining REE data and other trace element data.

No description available.

Steam reforming is a well established industrial process for the formation of synthesis gas. It takes place in two reversible stages: the reforming reaction (1) followed by the water-gas shift reaction (2). (1) CnH2n+2 + nH2O nCO + (2n+1)H2 (2) CO + H2O CO2 + H2 Reaction (1) is highly endothermic and is favoured at high temperatures and low pressure, while reaction (2) takes place at as low temperature as possible. One of the major problems affecting the steam reforming industry is catalyst deactivation due to sulphur poisoning. Sulphur is present in the hydrocarbon feedstock and even after desulphurisation steps some sulphur still remains, from ppb to ppm levels. Such low levels of sulphur can still poison the catalyst due to the catalyst having a significant time on stream. It is therefore desirable to produce a catalyst that exhibits sulphur resistance to prolong the lifetime of the catalyst. In this project the behaviour of precious metal catalysts (Rh and Pt supported on La-ZrO2, Al2O3 and SiO2) towards sulphur was examined. Two major aspects were studied, the catalysts’ adsorpitive behaviour towards sulphur and the effect of sulphur during the steam reforming reaction. Low pressure pulses of H2S and CH3SH over the catalysts followed by gas chromatography revealed that sulphur is a very strong adsorbing species, similar to CO, and could not be displaced by the adsorption of another species as there was no mechanism to desorb the sulphur species. The alumina supported catalysts offered some protection from sulphur poisoning, evidenced during co-adsorption experiments with CO, because the support was acting as a ‘sulphur sink’. Adsorption mechanisms were proposed for H2S at the different adsorption conditions tested: a 3-site adsorption mechanism producing surface sulphides at room temperature and at higher temperatures bulk sulphides were formed. High pressure steam reforming reactions of ethane were carried out at three different temperatures (600oC, 550oC and 500oC) to act as standards to the poisoned reactions, but also revealed interesting insights into the reforming of ethane. Each catalyst produced a unique reaction profile during steam reforming, with the La-ZrO2 catalyst exhibiting greatest activity. The Rh catalysts showed high selectivity towards the formation of CH4 due to the hydrogenolysis of C2H6, which was not occurring over the Pt catalysts. The Pt catalysts were the least active and deactivated considerably as the result of carbon formation. Sulphur species, hydrogen sulphide and methanthiol, were introduced into the reaction by dissolving them in the feed water. It was found the identity of the sulphur species had a significant impact upon the extent of catalyst deactivation, with methanthiol having the most detrimental effect, which was attributed to the molecule decomposing and laying down carbon. None of the catalysts tested exhibited particularly high sulphur resistance, particularly with regard to methanthiol, however Rh/ZrO2 did recover a lot of its original activity once the poison was removed from the feed. This was due to the removal of surface carbon rather than the removal of sulphur from the catalyst, because La-ZrO2 has a faster rate of oxygen transfer and therefore a mechanism to remove surface carbon.

Understanding the behaviour of heavy metals involved in the nuclear fuel cycle is of paramount importance to the reprocessing and storage of spent nuclear fuel. These studies have attempted to obtain a greater understanding of the fundamental chemistry of these systems, by investigating extraction performance and speciation in current (PUREX) and proposed (GANEX) extraction processes. Various complexes have been shown to exist in the post-extracted organic fraction of the systems analysed. For Zr(IV), U(VI) and Np(VI) separated from aqueous nitric and hydrochloric using TBP, the complexes [Zr(NO3/Cl)4(TBP)4], [UO2(NO3/Cl)2(TBP)2] and [NpO2(NO3/Cl)2(TBP)2] formed, respectively. For Zr(IV) separated from aqueous mixtures of HNO3 and HCl at equal concentration, a preference was shown to [Zr(Cl)4(TBP)4] over the analogous nitrate complex. For U(VI) separated from aqueous mixtures of HNO3 and HCl, a preference was shown to [UO2(Cl)2(TBP)2], even at high aqueous nitrate concentrations. NMR data for Pu(IV) separated from aqueous HNO3, HCl and mixtures of both, using TBP were presented, where possible complexation was observed. It is thought that [Pu(NO3)4(TBP)4] or [PuCl4(TBP)4] species existed within the organic fraction for Pu(IV) separated from aqueous HNO3 and HCl, respectively. These systems showed high distribution ratios where an increase was observed with increasing aqueous acid concentration overall. Distribution ratio data were presented for the lanthanide series separated from aqueous nitric acid, using the proposed GANEX solvent system(s). The lanthanides analysed showed an increase in distribution ratio with increasing aqueous nitric acid concentration and with increasing TODGA concentration in the organic fraction. Heavier lanthanides were observed to give higher distribution ratios overall. The best distribution ratios were observed for lanthanides separated using 0.2 M TODGA with 1-octanol (5 % by volume) over the nitric acid concentration range analysed. For lanthanides separated using 0.5 M DMDOHEMA, an optimum distribution ratio was observed at around 6 M aqueous nitric acid concentration. The distribution ratio data for lanthanides separated from a range of DMDOHEMA concentrations, were observed to increase with increasing organic DMDOHEMA concentration. The distribution ratios observed for isotopes of Np, Am, Eu and Pu separated using 0.2 M TODGA, increased with increasing aqueous nitric acid concentration. The same trend was observed for the aforementioned isotopes separated using 0.5 M DMDOHEMA. However, pertechnetate separated using 0.2 M TODGA from aqueous nitric acid, showed a decrease in the distribution ratios observed over the acid concentration range analysed. This was contrary to pertechnetate separated from aqueous nitric acid using 0.5 M DMDOHEMA, where a small increase in distribution ratio was observed over the concentration range analysed. For Np(VI) separated from some proposed GANEX solvents, the 0.2 M TODGA/0.5 DMDOHEMA combination gave the best distribution of neptunium into the organic fraction. For Np(VI) separated using 0.5 M DMDOHEMA, the complex [Np(DMDOHEMA)2(NO3)4] was observed. Additional attempts to analyse Np(VI) behaviour under GANEX style conditions via EXAFS, were not successful due to immediate reduction of the Np(VI) on the beam line.

Oceanic barium has many potential proxy applications, from the quantification of export productivity using sedimentary barite, to the tracing of freshwater inputs or the circulation of deep water masses. Using these proxies to reconstruct past oceanic conditions is of particular importance in the Southern Ocean, where the ventilation of deep water masses and the biological drawdown of CO2 are thought to play a significant role in climate regulation. However, the distribution of particulate and dissolved barium in this region is not solely controlled large scale water mass circulation and predictable biological associations, but by an additional combination of spatially and temporally variable local and coastal processes. In this thesis I have found that stronger near-surface gradients are observed in Antarctic waters than in other ocean basins, with a significant association between Bad and silicic acid in surface waters at the WAP. As no direct link was observed between Bad and biological productivity, these observations can be explained by an association between Bad and siliceous detrital material, either by adsorption mechanisms or through barite precipitation in surface waters. Greater levels of Bad release and inferred barite precipitation production are observed from the decay of diatom-dominated detrital material. The accumulation of particulate barium phases in WAP shelf sediments appears to produce a benthic Bad flux that acts as a significant source of Bad to coastal waters. Sea ice is found to be a further, little studied, control on Antarctic coastal Bad distributions, with non-conservative distributions of Bad observed in sea ice cores that may be due to abiotic barite precipitation, and large fluxes of sea ice melt associated with unusually low surface Bad concentrations.

The karst-associated bauxites of the Parnassos-Ghiona zone in Central Greece are part of the large Mesozoic age Mediterranean Karst Bauxite belt. Greece is responsible for around 50% of European bauxite production, and has an estimated 600 million tonnes of bauxite reserves. This investigation focuses on the bauxites of Mount Iti and Mount Ghiona, two mountains in the west of the Parnassos-Ghiona zone that are currently being explored and mined by Greek bauxite producer, Elmin S.A. The aim was to develop a better geological understanding of the ore genetic history and regional structural evolution to aid ore deposit science and bauxite exploration. Within the Parnassos-Ghiona zone the bauxites were deposited as three separate ore horizons intercalated with thick limestone layers during the early Jurassic, late Jurassic and late Cretaceous. Only the upper two bauxite horizons are economic and therefore formed the focus of this investigation.

Der Band fasst den Kenntnisstand zu den Komplexlagerstätten östlich von Pöhla zusammen. Behandelt werden die Nebengesteinsverhältnisse mit der Tektonik, die Vererzungsverhältnisse und Fragen zu den geophysikalischen Arbeiten in der Lagerstätte, zur Hydrogeologie und zur Ingenieurgeologie. Die Untersuchungen zur Entwicklung der Rohstoffbasis zeigen, dass noch beträchtliche Vorräte in der Tiefe verblieben sind, insbesondere an Zinn.