Caradocian phosphorite nodules sampled from the Powys county of N. Wales, U.K. have been investigated in order to characterize the deposit geochemically, mineralogically and petrographically and to evaluate their mode of formation. Nodules are the main form of phosphorite although phosphatized organic fragments and oolitic grains are also present. On the basis of petrographio characteristics, nodules are grouped into two types; Type I nodules (with abundant organic material) and Type II nodules (with abundant clay minerals). Mineralogical compositions of the phosphorite nodules reflect varying degrees of dilution of the phosphate material, francolite, by authigenic and detrital minerals. Examination with the scanning electron microscope of freshly fractured surfaces of nodules suggests that the apatite formed authigenically as a direct chemical precipitate. Surfaces of abundant siliceous spicules and other organic fragments as well as some minerals appear to be favoured sites for apatite nucleation. Geochemical studies showed significant impoverishment of lattice elements and enrichment of non-lattice elements in both types of nodules. Chemically the phosphorite nodules may be described in terms of four major components: SiO2, CaO, P2O5 and F. The average concentrations of trace elements present in these nodular phosphorites were compared with an average concentration in marine shales. The enrichment and/or depletion largely suggested precipitation from sea water. The proposed model of phosphorite formation involves inorganic (or biochemical) precipitation of apatite within pore waters of anoxic sediments and subsequent concentration of the apatite by physical processes. Oxidation of organic material during sulphate reduction is the main source of phosphate. This is supported by the very light delta13c isotopic composition of structural carbonate present in the francolites. These studies have also shown that these phosphorites have undergone differential leaching during weathering processes with the development of secondary phosphate: minerals, decarbonation of francolite and removal of many major and minor elements.

L’hydroxyapatite est un biomatériau bioactif largement utilisé pour la réparation et la reconstruction des défauts osseux, cependant, son efficacité est souvent limitée par sa faible densité. Le présent travail constitue une nouvelle contribution à l’étude des biocéramiques compacts nanostructurés qui sont considérés comme étant des matériaux facilement implantables au niveau osseux et dentaire. Des nanoparticules anisotropes d’hydroxyapatites ont été synthétisées par hydrolyse forcée en milieu polyol, en vue d’améliorer les caractéristiques mécaniques des biocéramiques apatitiques. Les nanopoudres obtenues ont été consolidées par le processus non-conventionnel tel que le frittage flash (spark plasma sintering, SPS) aboutissant à des massifs d’hydroxyapatites nanostructurés 3D. Ces derniers ont montré des performances morphologiques similaires à celles utilisés dans l’industrie, d’autre part, elles ont montré des performances mécaniques améliorées avec une dureté allant jusqu’à 9 GPa. / Hydroxyapatite is a biomaterial bioactive largely used for the reparation and the reconstruction of the bone and dental defects. However, the performance of the hydroxyapatite is limited by its low density. The present work forms a new contribution in the study of compact nanostructured biomaterials. These later are considered as facile implantable materials to bones ant dents. Anisotropic nanoparticle hydroxyapatites were synthesized by forced hydrolysis in a polyol medium in order to ameliorate the mechanic characteristics of bioceramic hydroxyapatites. The obtained nanopowders were consolidated by the nonconventional process spark plasma sintering (SPS) resulting to 3D nanostructure massive hydroxyapatites. The morphological performances were found to be similar to that which used in industries. On the other hand, the elaborated massive nanostructures have shown an ameliorated mechanical performance with 9 GPa hardness.

A study has been conducted on the loss of phosphate ions and excessive oleic acid consumption encountered in the selective flotation of dolomite from apatite. An attempt has been made to evaluate the mechanism by which orthophosphate ions depress apatite flotation. Replacement of SO₄⁻² ions on gypsum by HFO₄⁻² ions is found to occur rapidly in solution. The presence of CaHPO₄⁻² 2H₂O on gypsum surfaces is shown using infrared reflectance spectroscopy. CaHPO₄⁻²H₂O is isomorphous with gypsum and has identical lattice parameters. Experiments show that the addition of sulfate ion to the system suppresses the reaction of orthophosphate ions with gypsum by the common ion effect. The proposed reversible reaction in the system is: CaSO₄∙2H₂O + HPO₄⁻²↼⇁ CaHPO₄ ∙2H₂O + SO₄⁻² A proposed mechanism by which orthophosphate ions selectively depress apatite flotation is shown to fit all experimental observations. Orthophosphate ions are known to be potential determining for calcite, dolomite and apatite. It is observed that in the presence of orthophosphate ions calcite and dolomite recovery is higher at pH 6.0 than at pH 8.5. Apatite and gypsum exhibit opposite behavior. It is proposed that the adsorption of strongly hydrogen bonding H₃PO⁴, H₂PO₄⁻² and HPO₄⁻² in the electrical double layer results in collector species being slow to penetrate and adsorb on the minerals. Acid attack on calcite and dolomite results in disruption of the hydrogen bonded layer and allows rapid collector adsorption. Two equally important effects of adsorbed phosphates are to decrease collector adsorption due to the large negative zeta potential generated and to impede fruitful particle-bubble interactions. Brittle froths encountered in flotation at pH 6.0 are related to condensation of surface films formed by oleic acid -sodium oleate complexes. The froth stabilizing effects of hydrophobic dolomite particles is noted. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

Although the technical literature contains abundant references on applications of starch in mineral processing, the majority is not concerned with phosphate mineral systems. Nevertheless, the interaction between starch and apatite surfaces is relevant to both selective flocculation and flotation of phosphate ores. The main objective of this thesis is to investigate in detail such interaction in order to provide a more clear understanding on the behaviour of apatite/starch systems. Considerable research effort was dedicated to a thorough characterization of the starch samples used, especially in those aspects most pertinent to the application of starches as flocculants and depressants. Presence of ionic impurities in the starch samples tested was identified by infrared spectroscopy and microelectrophoresis. These impurities (proteins, carboxylic groups and, possibly, phosphate esters)were found to play an important role in the mechanisms governing the interaction of starch macromolecules and mineral surfaces. In a first stage of this research, the interaction between aqueous solutions of starches (and starch fractions - amylose and amylopectin) with calcium ionic species and surfactants (flotation collectors) was investigated. Depression of solution electrical conductivity, experienced in Ca-starch systems, was indicative of chemical reactions taking place (complexation). For surfactants, evidence for their interaction with starch fractions was obtained by UV-Vis. spectroscopy. The spectra of starch/surfactant solutions in the presence of iodine were altered indicating the substitution of iodine species by surfactant molecules at the helical sites of starch macromolecules. The next step involved the study of the adsorption of starch onto both apatite and silica mineral surfaces. Preliminary tests pointed out that a much stronger interaction took place in the case of apatite. Starch adsorption isotherms obtained for fluorapatite and quartz confirmed the preferential adsorption of starch onto the phosphate mineral surface. Both amylose and amylopectin were strongly adsorbed on fluorapatite but the latter polymer displayed the largest extent of interaction on a weight per area basis. The shape of the adsorption isotherms for the two starch fractions on fluorapatite also corroborates the idea of a stronger interaction by amylopectin. In turn, whole starches displayed adsorption isotherms resembling more closely that obtained for amylopectin. Adsorption of starches on fluorapatite was increased considerably in the presence of Ca ionic species. In the absence of externally added Ca ionic species, the amount of Ca released by the mineral surface was dependent upon the amount of starch adsorbed. These two phenomena can be interpreted as indicating the importance of Ca sites and presence of Ca species for the adsorption of starches, hence justifying the preferential adsorption displayed for apatite. Adsorption of starch on quartz surfaces was also enhanced in the presence of Ca ionic species, once more confirming the important role played by calcium on the adsorption of starches. Flocculation studies were also conducted with fluorapatite, kaolinite and quartz suspensions in the presence of different starches. Under the conditions tested, all starches samples failed to promote aggregation of the two non Ca-bearing minerals. In turn, fluorapatite suspensions were flocculated rather strongly by all starches. Maximum flocculation of fluorapatite was achieved at partial polymer coverage conditions. With one exception (amylose), increasing the concentration of the polymers above an optimum level, generated partial re-stabilization of the suspensions, probably via a steric effect. All starches depressed both anionic and cationic flotation of fluorapatite. Amylose was the least effective depressant among all starches, especially for the cationic flotation system. The depressant action was a function of pH and of the relative amounts of polymer and surfactant. Alkaline pH favoured depression, whereas as the collector level was increased, the depressant action was diminished and eventually eliminated. The experimental evidence gathered in the present research supports a chemical mechanism for the interaction between starch and apatite surfaces. Calcium plays a dominant role, and its importance for the adsorption of starches onto mineral surfaces is most probably related to the formation of complexes between starch impurity-related ionic groups and Ca ionic species. Hydrogen bonding and to lesser extent electrostatic forces are also important for the overall interaction between starch and apatite surfaces. The larger extent of interaction for the amylopectin fraction(highest molecular wt.) as compared to that of amylase (lowest molecular wt. fraction) gives support for the accessory role of hydrogen bonding. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

Dissolution experiments were conducted on bioapatite at 4°C, 21°C and 38°C and solution pH values between 2 and 8 in a stirred tank reactor. The bioapatite was obtained from modern white-tailed deer (Odocoileus virginianus) scapulae, crushed, and cleaned in 30% hydrogen peroxide to remove organic matter. The average BET specific surface area of the 75-106 and 106-246 μm particles was 255 m2 g-1. During experiments the ratio of Ca:P released became stoichiometric at ca. 1.44. The following dissolution rate law was derived from the experimental results: R = K1(H+)ⁿ+K2 in which R is the dissolution rate (mol bioapatite m-2 s-1) based on the bioapatite stoichiometry, n = 1.01 ± 0.15, k1 = 1.84 x 10-6 ± 1.71 x 10-6 mol m-2 s-1, and k2 = 4.29 x 10-10 ± 1.15 x 10-10 mol m-2 s-1 and H+ is the hydrogen ion activity. From 2 < pH < 4, dissolution rate is dependent on pH and becomes independent of pH from 4 < pH < 8. These results for modern bone may be compared with previous investigations of igneous (FAP) and phosphorite-derived sedimentary carbonate fluorapatites (CFA)(e.g., Guidry and Mackenzie, 2003). At pH = 6, in the pHindependent region, dissolution of the modern bioapatite was ca. 7 times faster than FAP and 100 times faster than CFA. The acid transition pH of the bioapatite (pH = 4) is lower than that for FAP (pH = 6). Bioapatite dissolution rates influence fossil preservation potential, the release rate of nutrients from bone meal fertilizers, the effectiveness of bone as reactive barriers to control pollutants and nuclear waste isolation, and as a feedstock material in CO2 sequestration processes. / Geology

Th.--Sci. phys.--Toulouse--I.N.P., 1977. N°: 23.

The Hoidas Lake Rare Earth Element (REE) Deposit is one of several REE showings which are spatially associated with a regional-scale fault system that cuts through the Rae Province in northern Saskatchewan. The showings occur along the Hoidas-Nisikkatch fault, believed to be a subsidiary of the Black Bay Fault, and consist of multiple REE-enriched veins. Surface outcrops and drilling have delineated a vein system, called the JAK zone, which extends for over 1 km along strike, with the system remaining open both along strike and down dip. The majority of the REE are hosted by fluorapatite and allanite-(Ce), although there are also minor amounts of monazite, bastnaesite and chevkinite which can contain significant concentrations of REE. The veins are dominantly LREE-enriched, specifically La, Ce, and Nd.<p> The mineralization at Hoidas Lake is complex, with the chemical and mineralogical compositions changing with each vein generation. The earliest veins consist of REE-bearing allanite and chevkinite which occur in association with clinopyroxene, titanite, and hyalophane. The allanite-rich veins are followed by veins dominated by red or green apatite, both of which are typically brecciated. Finally, there is a late apatite which crosscuts all previous vein generations. Each of the distinct apatite generations shows discrete chemical variations, particularly in their light rare earth element content, with the total rare earth oxide content ranging from approximately 1.5% in the oldest apatite to as much as 5% in the green apatite.<p> The majority of the apatite and allanite crystals are strongly zoned, reflecting the chemical changes in the mineralizing system through time and, particularly in the earliest vein generations, there are signs of hydrothermal alteration. The early apatite generations typically show the development of monazite inclusions which suggests interaction with hydrothermal fluids, as do the REE-poor rims and bastnaesite alteration observed in the majority of the allanites.<p> The veins are fault controlled and are interpreted to be late magmatic- hydrothermal in origin, with the fluid derived from a magmatic source at depth. Although the exact source of the fluids remains uncertain, the high concentration of REE, as well as Sr and Ba, and a relative depletion in high field strength elements suggests that the mineralization may be related to either an alkali or carbonatitic source.

The Hoidas Lake Rare Earth Element (REE) Deposit is one of several REE showings which are spatially associated with a regional-scale fault system that cuts through the Rae Province in northern Saskatchewan. The showings occur along the Hoidas-Nisikkatch fault, believed to be a subsidiary of the Black Bay Fault, and consist of multiple REE-enriched veins. Surface outcrops and drilling have delineated a vein system, called the JAK zone, which extends for over 1 km along strike, with the system remaining open both along strike and down dip. The majority of the REE are hosted by fluorapatite and allanite-(Ce), although there are also minor amounts of monazite, bastnaesite and chevkinite which can contain significant concentrations of REE. The veins are dominantly LREE-enriched, specifically La, Ce, and Nd.<p> The mineralization at Hoidas Lake is complex, with the chemical and mineralogical compositions changing with each vein generation. The earliest veins consist of REE-bearing allanite and chevkinite which occur in association with clinopyroxene, titanite, and hyalophane. The allanite-rich veins are followed by veins dominated by red or green apatite, both of which are typically brecciated. Finally, there is a late apatite which crosscuts all previous vein generations. Each of the distinct apatite generations shows discrete chemical variations, particularly in their light rare earth element content, with the total rare earth oxide content ranging from approximately 1.5% in the oldest apatite to as much as 5% in the green apatite.<p> The majority of the apatite and allanite crystals are strongly zoned, reflecting the chemical changes in the mineralizing system through time and, particularly in the earliest vein generations, there are signs of hydrothermal alteration. The early apatite generations typically show the development of monazite inclusions which suggests interaction with hydrothermal fluids, as do the REE-poor rims and bastnaesite alteration observed in the majority of the allanites.<p> The veins are fault controlled and are interpreted to be late magmatic- hydrothermal in origin, with the fluid derived from a magmatic source at depth. Although the exact source of the fluids remains uncertain, the high concentration of REE, as well as Sr and Ba, and a relative depletion in high field strength elements suggests that the mineralization may be related to either an alkali or carbonatitic source.

The Trans-Suture Suite (TSS) of granitic plutons located in Northern Britain span the Iapetus Suture and represent a particularly enigmatic stage of post-Caledonian Devonian magmatism. Despite calc-alkaline affinities, proximity to the Iapetus Suture precludes a direct relationship to active subduction. Furthermore, the absence of inherited zircons distinguishes the TSS from plutons of a similar age throughout the Scottish Highlands, and is not easily reconciled with the abundance of peraluminous and S-type granites. Micro-analytical techniques are employed to analyse accessory zircon and apatite from three TSS plutons (Criffell, Fleet and Shap) in order to investigate connections between magmatic and tectonic processes within a continental suture zone. Accessory minerals contain a robust and accessible record of magma evolution. However, their trace element compositions are shown to document the final stages of pluton emplacement only, and are determined primarily by competitive crystallisation of other accessory phases at shallow crustal levels. By contrast, whole-rock compositions record an earlier stage of magma evolution that occurred in deeper and open-system crustal hot zones. The absence of inherited zircon in the final crystal assemblage reflects resorption during rapid and potentially adiabatic ascent of super-liquidus and water-rich magmas from the crustal hot zone. The concentrations of REE in apatite inclusions decrease with increasing crystallisation of other accessory minerals and in some samples have been distinguished on the basis of their host phase. In metaluminous granodiorites, no preferred crystallisation sequence is observed between host phases. In peraluminous samples, zircon-hosted apatite compositions appear more primitive compared to those hosted by other phases and reflects earlier saturation of zircon in these magmas. The isotopic record of zircon is shown to be biased towards earlier stages of magma evolution in peraluminous magmas and provides a means of assessing zircon isotope compositions in the context of often protracted histories during silicic magma evolution. The Mn content of apatite varies independently to whole-rock composition, correlating positively with decreasing oxygen fugacity and indices of increasing reduction. Apatite is proposed as a robust and effective redox proxy with application to magmatic, detrital and lunar studies of redox conditions. Zircon O-HfU- Th-Pb isotope compositions have identified increasing degrees of compositional heterogeneity in more silicic components of the TSS, including the involvement of more mafic magmas in the generation of the large S-type pluton of Fleet. Compositional trends between zircons from plutons emplaced on both sides of the Iapetus Suture are used to identify a common Avalonian component beneath the Southern Uplands and English Lake District related to Avalonian underthrusting beneath the Laurentian margin during the late Caledonian. New geochronological dating indicates that pluton emplacement occurred during periods of both pre- and post-Acadian transtension. The distinguishing characteristics of these plutons relative to other Caledonian plutons reflect their unique emplacement into the hydrated lithosphere of the Iapetus Suture Zone. Oxygen isotope disequilibrium between the magmatic compositions recorded by zircon and those of the whole-rock and some quartz crystals reflect hydrothermal alteration of the latter two archives. Hydrothermal alteration and exchange caused by 18O-rich magmatic fluids has elevated the 18O compositions of the whole-rock and some quartz crystals, with most disequilibrium observed around the outer margins of the plutons due to further fluid interaction with local 18O-rich sediments. The hydrothermal history of the TSS is markedly different from that of the British Tertiary Igneous Province where hydrothermal alteration resulted from circulation of meteoric water, reflecting significantly different magmatic and emplacement histories.

Thesis (M.S.)--Missouri University of Science and Technology, 2008. / Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed May 9, 2008) Includes bibliographical references (p. 131-139).