High Fe2O3 Content Research Articles

U-Pb detrital zircon ages and compositional features of Bifurto quartz-rich sandstones from Southern Apennines (Southern Italy): comparison with Numidian Flysch sandstones to infer source area

Two samples of quartz-rich sandstones belonging to Bifurto Formation in Southern Apennines, were studied for their petrographical, geochemical and geochronological (U-Pb detrital zircon ages) features and compared with those of sandstones from five stratigraphic sections of the Numidian Flysch in SouthernItaly. The purpose of this comparison is to assess the homogeneity and provenance of detritus because quartz-rich sandstones of both formations are coeval having Burdigalian p.p. - Early Langhian age.The depositional domain of the Bifurto formation was located on the sinking Campania-Lucania carbonate platform whereas that of Numidian Flysch was within the Lagonegro-Molise Basin east of the Campania-Lucania Platform. The Bifurto sandstones have sub-arkose - quartzarenitic composition with high Fe2O3 contents (Fe2O3 in the range 2.85 wt% - 4.83 wt%), however, the whole composition varies in the same compositional range of the Numidian Flysch sandstones.The U-Pb detrital zircon ages in Bifurto sandstones range from 2551±40 Ma to 425±9 Ma and 93% of these age data is comprised in the same time lapse of detrital zircon ages of Numidian Flysch sandstones (3047±13 to 516±19 Ma). These ages suggest a provenance area consisting of ancient orogens in which Precambrian and Silurian rocks are present. The absence of Paleozoic - Mesozoic ages excludes provenance from Variscan or Alpine rocks. On this basis, the African Craton represents the exclusive source area of Bifurto sandstones as well as of Numidian Flysch sandstones outcropping in Southern Apennines. Similar deductions have been proposed for Numidian sandstones outcropping along the Betic and Maghrebian chains from Spain to Morocco, Algeria and Sicily.

The ash formation and attrition characteristics of an Indonesia lignite coal ash for a 550 MWe ultra supercritical CFB boiler

The Samcheok CFBC (circulating fluidized bed combustion) power generation plant, the world largest, consists of 4 units of 550 MWe USC (ultra-supercritical) CFB boilers, started operation since the end of 2016. The years’ operation proves that there lacks circulating material and low solid hold-up in the upper furnace when burning Indonesia coal with low ash content of 4.5%. To solve this problem, the present study studied the mass balance of the Samcheok CFB boiler by investigating the ash formation and attrition characteristics of the feed coal in the lab. The ash formation PSD (particle size distribution) proves that the burnout-produced fly ash and fragmentation-produced fly ash are not the main sources of the production of fly ash. The heterogeneity of specific chemical compositions of particles in terms of particle sizes is proved to be one of the key factors for determining the attrition rate. For large particles, SiO2 and Al2O3 compositions dominate and results in low attrition rate, while for small particles, Fe2O3 and CaO compositions dominate and results in high attrition rate. The fine particles produced due to attrition have very high Fe2O3 contents, indicating that the heterogeneity of chemical composition is enhanced due to attrition. These findings show good agreement with the phenomenon of the high content of Fe2O3 in fly ash in the CFB boiler.

Assimilation of the mafic‐ultramafic magma: a case study of diabase dyke at the Beidaihe, North China Craton

AbstractAssimilation serves as a significant part in magma's evolution. Because of rapid cooling of ultramafic‐mafic magma, assimilation between mantle‐derived magma and crustal rocks (wall‐rocks) is often neglected. The Beidaihe diabase dikes in North China Craton suggest that assimilation of the rapidly cooled mantle‐derived magma can not be ignored. The diabase dikes are very thin (0.5 to 2 m in width) and discordantly intrude into Ordovician limestone. Center of dyke is porphyritic texture while chilled margin of it is aphanitic texture, suggesting a rapid crystallization process. Moreover, limestone close to the dyke was transformed into marble because of contact‐thermal metamorphism. From the center to margin of the dykes, contents of SiO2 (48.9→ 41.6 wt.%) and MgO (8.3 → 4.0 wt.%) are obviously decreased, but contents of CaO (6.4→8.3 wt.%) and CO2 (0.8 → 5.2 wt.%) are distinctly increased. Meanwhile, calcites in the wall rocks adjacent to and far from the dykes are also greatly different. The calcites close to the dykes have high MgO and FeO contents but low CaO and CO2 contents. All these suggest an assimilation process of the mantle‐derived magma with wall‐rock limestone. Calculating CO2 contents in the dyke and wall rock suggest that the extent of assimilation is thought to reach up to 8 ‐ 12 %. Therefore, when the wall rocks of the mantle‐derived magma are carbonate rocks, its components are obviously influenced by assimilation, although it often rapidly chilled. Simultaneously, this study provides possible explanation for some mantle‐derived rocks in carbonate areas with high LOI.

Zircon U–Pb geochronology, Hf isotopic compositions, and petrogenetic study of Abor volcanic rocks of Eastern Himalayan Syntaxis, Northeast India: Implications for eruption during breakup of Eastern Gondwana

This paper reports new zircon U–Pb ages and Hf isotopic compositions of felsic units of the Abor volcanic rocks (AVR) of Eastern Himalayan Syntaxis (EHS), Northeast India, and discusses their relationship to the Kerguelen plume activity. The AVR are bimodal and predominantly constituted by mafic rocks with minor felsic units. Mafic volcanics are identified as basalt and basaltic andesite with light rare earth elements (LREE) enriched and slightly depleted heavy rare earth elements (HREE) pattern without Eu anomalies. Low concentrations of LILE, high contents of Fe2O3, and other incompatible trace elements ratios reflect enriched nature of these mafic volcanics. Felsic volcanic rocks are dacitic to rhyolitic in composition, which have high REE content, high LREE/HREE, and pronounced negative Eu anomalies. Enriched LREE, high Th/Nb, Ce/Nb ratios, and variations in Rb/Zr, K/Rb, La/Sm ratios with negative anomalies of Ba, Nb, Sr, P, Ti in felsic rocks suggest substantial contribution of crustal contamination at the time of eruption. Zircons from felsic units yield an average U–Pb age of ~132 Ma and unradiogenic (ƐHf(t) < 0) Hf isotope values of −7.0 to −13.3 with model ages between 1.5 and 2.1 Ga, suggesting old crustal assimilation in their genesis. The AVR were emplaced in the continental rift tectonic setting, and depth of the magma source is confirmed as near spinel stability zone. The AVR are positively comparable with other flood basalts that were formed due to the Kerguelen plume activity. Therefore, our combined new geochemical and geochronological data show that the AVR were emplaced at early stage (~132 Ma) of eastern Gondwana breakup due to outbreak of the Kerguelen plume. This study thus supports the idea of the Kerguelen plume affecting a large area of Eastern India, Western Australia, and Antarctica during early stage of Gondwana breakup.

Subduction and rollback of the paleo-Pacific plate during the Early Cretaceous: Insights from the Jiangmiao gabbroic intrusion in the Lower Yangtze River Belt, central-eastern China

The dynamics of Mesozoic tectonism recorded by the Lower Yangtze River Belt (LYRB), located in central-eastern China, are controversial. Between 148 and 123 Ma, three major and continuous stages of magmatism occurred in the LYRB: 1) high-K calc-alkaline intrusions, 2) andesitic shoshonitic volcanism, and 3) A-type granitic intrusions. The Jiangmiao gabbroic intrusion, which is located at the eastern end of the LYRB, is composed of gabbro and diorite and was emplaced at ~124 Ma (Dong et al., 2017; Sun et al., 2017a), simultaneous with the A-type granites of the third stage of Mesozoic magmatism in the LYRB. Petrography and mineral chemistry indicate that the Jiangmiao intrusion was formed by the intense crystal fractionation of an oxidized (ΔNNO ca. +1.0) and hydrous (3.5–4.5 wt% H2O) basaltic magma that produced the evolved dioritic magma and gabbroic cumulate. The accumulation of magnetite, olivine, clinopyroxene, and plagioclase resulted in abnormally high Fe2O3 (12.44–16.30 wt%) and low SiO2 (40.75–45.88 wt%) contents in the gabbro, as well as the enrichment of TiO2, Sr, Cr, Ni, Co, and V in the gabbro compared with the diorite. Intense crystal fractionation coupled with the fluid transport led to the enrichment of highly fluid-mobile elements (Rb, Th, U, and Pb) in the evolved diorite but depletion of these elements in the gabbro. The mineral chemistry of clinopyroxene and whole-rock Sr−Nd−Pb isotopic compositions indicate that the primitive basaltic magma originated from the partial melting of an enriched lithospheric mantle source in a subduction environment, but more asthenosphere mantle components were incorporated into the magma source compared with the earlier Mesozoic magmatic rocks in the LYRB. The coevality of the Jiangmiao gabbroic intrusion and the A-type granites supports the tectonic model of Mesozoic rollback of the westward-subducting paleo-Pacific plate. The Jiangmiao gabbroic intrusion likely represents the edge of the back-rolling slab at ~124 Ma, whereas the simultaneous A-type granites in the middle of the LYRB were formed as a result of intraplate extension generated by rollback.

Phosphate Capacities of CaO–FeO–SiO2–Al2O3/Na2O/TiO2 Slags

Abstract To effectively increase the dephosphorization efficiency of hot metals or the previous stage in the converter steelmaking process, phosphate capacities ( C P O 4 3 − ) {\rm{(}}{{\rm{C}}_{{\rm{PO}}_4^{3 - }}}) of CaO–FeO–SiO2–Al2O3/Na2O/TiO2 slags at 1300–1400°C were examined by laboratory experiments using equilibrating slag and pure solid iron foil. The data suggested that ( C P O 4 3 − ) {\rm{(}}{{\rm{C}}_{{\rm{PO}}_4^{3 - }}}) increases with decreasing temperature and increasing slag basicity. Compared to basicity, temperature considerably affected the phosphate capacities and tended to be the most important factor. The phosphate capacities of slag considerably decreased at a high temperature of 1400°C even under high binary basicity as well as high contents of Na2O and FeO. Moreover, with the increase in the content of FeO and Al2O3 in the slag, ( C P O 4 3 − ) {\rm{(}}{{\rm{C}}_{{\rm{PO}}_4^{3 - }}}) decreased. A low content of Na2O led to the increase in the phosphate capacities of slag, particularly at low temperatures of 1300–1350°C. The content of TiO2 in the slag considerably exhibited a weaker effect on ( C P O 4 3 − ) {\rm{(}}{{\rm{C}}_{{\rm{PO}}_4^{3 - }}}) . Furthermore, by regression analysis, ( C P O 4 3 − ) {\rm{(}}{{\rm{C}}_{{\rm{PO}}_4^{3 - }}}) was expressed as a function of the temperature and slag compositions as follows: logC PO 4 3 − = 0.041 ( % CaO ) − 0.086 log ( % FeO ) − 0.024 ( % SiO 2 ) − 0.02 ( % Al 2 O 3 ) + 0.067 ( % Na 2 O ) + 0.039 ( % TiO 2 ) + 56767 / T − 14.58 , ( R = 0.978 ) \eqalign{&{{\rm{log}}{{\rm{C}}_{{\rm PO}_4^{3 - }} = 0.041( \% {\rm CaO}) - 0.086{\rm log}({\rm{ \% }}{\rm FeO})} - 0.024( \% {\rm Si{O_2}})} \cr &{{ - 0.02({\rm{ \% }}{\rm A{l_2}{O_3})}} { + 0.067( \% {\rm N{a_2}O)} + 0.039( \% {\rm Ti{O_2})}}} \cr &+ 56767/{\rm T} - 14.58, ({\rm R} = 0.978)}}

Meso-Neoarchean magmatism and episodic crustal growth in the Kudremukh-Agumbe granite-greenstone belt, western Dharwar Craton, India

Mafic volcanic rocks and dykes associated with Na-rich TTG and K-rich granites in the Kudremukh greenstone belt of western Dharwar Craton provides a window to Precambrian crustal evolution in the southern Peninsular India. Here we present zircon U-Pb geochronology and geochemistry of these rocks to constrain the greenstone-basement relationship and crustal growth events in the western Dharwar Craton. TTGs exhibit fractionated REE patterns [(La/Yb)N = 11.8–50.3; (Gd/Yb)N = 2.1–4.9] whereas the granites with K2O contents of 3.84–5.20 wt% are peraluminous calc-alkaline with moderate enrichment of LREE over HREE and depleted MREE abundances. The metabasalts are characterized as arc basalts with moderate to high Fe2O3, CaO, SiO2, MgO, LILE, LREE and low HFSE contents. The higher Nb contents (6.2–11.4 ppm) in some of them, classified as Nb-enriched basalts, were erupted at 2498 ± 43 Ma, indicating a 2.5 Ga greenstone volcanism in the western Dharwar Craton. These are characterized by slightly fractionated REE along with negative Nb, Zr, Hf and Ti anomalies. The amphibolitic and doleritic dykes have overlapping chemistry with moderate Al2O3, moderate to high Fe2O3 and MgO displaying coherent chondrite normalized REE patterns. The 3068 ± 34 Ga TTG were generated through high pressure melting of mafic crust in a garnet-spinel peridotite mantle regime with the assimilation of upper crustal material in a subduction zone environment. The granites of 2936 ± 23 Ma were the products of partial melting and fractional crystallization of TTG melts which display intrusive relationship with the thickened TTG crust. The mafic volcanism took place at 2498 ± 43 Ma subsequently followed by the dyke emplacement at 2484 ± 29 Ma. Therefore, two major episodes of crustal growth are identified from this region: i) TTG-granite association ∼3.0–2.9 Ga and ii) mafic volcanism – dyke emplacement between 2.49 and 2.48 Ga. The geochemical signatures of arc basalts and Nb enriched basalts indicate variable slab-mantle interactions including fluid-fluxed metasomatism and melt-fluxed hybridization of mantle wedge in a subduction zone environment followed by the emplacement of amphibolitic dykes during post-subduction collision phase. Our results document the episodic growth of continental crust in western Dharwar Craton from 3.0 to 2.5 Ga.

Optimal Cooling Rate of Porous Fill Based on Liquid-Glass Compositions

The composition and a method of production are proposed for high-porosity materials in low-temperature foaming of liquid glass and ash-slag material from burning of combustible shales used as fill and consumable additives. It is shown that keramzit based on liquid glass must be cooled at the rate 60 K/min, because a porous material with high structural quality factor and with high FeO content is formed at this cooling rate.

Genetic relationship between fenitized ores and hosting dolomite carbonatite of the Bayan Obo REE deposit, Inner Mongolia, China

The Bayan Obo deposit is the largest rare-earth element (REE) deposit in the world. In this deposit, ore bodies are hosted in fine-grained ore-bearing dolomite marbles, known as the H8 dolomite marble. The H8 dolomite marble has been considered as part of the Bayan Obo Group composed Paleoproterozoic sedimentary rocks. However, the H8 dolomite marble can be younger than the Bayan Obo Group, and thus, the genesis of the dolomite marble should be re-examined. In this paper, we describe petrography and compositions of the H8 dolomite marble. The dolomite marbles generally have high FeO, MnO and SrO contents, different from sedimentary limestone or dolostone but similar to dolomite carbonatites. In composition, they can be grouped into magnesio-carbonatite and ferro-carbonatite. Texturally they are porphyritic and comprise originally hypabyssal intrusions. It is thus proposed that carbonatitic magmas injected slowly into a magma chamber where they have undergone fractionation to produce evolved dolomite-carbonatite magmas rich in alkali, REE, Fe and volatile components. Such evolved, metal-rich magmas were consequently injected along the contact zone between the early dolomite carbonatite sill and other layer of the Bayan Obo Group, and produced an large fenitization aureole enclosing ores rich in Fe, Nb, REE, F and alkali metals. Changes in CO2/H2O ratios, oxygen fugacity and halogen content of fluids were responsible for the formation of different types of ore, including massive magnetite-rich, aegirine-rich and Na-amphibole-rich ores. Considering the fact that the ore bodies are located at the place where dolomite carbonatites are relatively thick and the fenitization is relatively extensive, we speculate that the ore formation was genetically related to extensive fenitization involving exsolution of large amounts of fluids and subsequently extensive metasomatism. It is concluded that carbonatitic magmas played a major role in the formation of the REE mineralization in the Bayan Obo deposit.

Geological and contaminant transport assessment of a low level radioactive waste disposal site

The protective function of a radioactive waste disposal is provided by natural geological barrier itself. Sand and sandstone samples were taken from Inshas rad-waste disposal site and were subjected to geochemical-physical examinations. The rock volumes of such samples were composed of 70% quartz and 10% plagioclase beside 17% interstitial matter. The weathering indices indicated moderate weathering of the source materials. Provenance studies suggested the derivation from recycled quartoze sediments. The presented high contents of the interstitial Fe2O3 (hematite/goethite) and Al2O3 (clay/kaolinite) were important agents for preventing pollutants transport via adsorption and the reduced porosity (10–20%) and permeability (0.1–6 md). Flow and transport of Cs+ and Sr2+ ions in groundwater was simulated using fixed bed sand column under the effect of initial ion concentration. Hights of mass transfer zones of Cs+ testing beds and their rates of movement and fractional capacities were found to be higher than those of Sr2+. The maximum adsorption capacities were calculated using Thomas and Yoon-Nelson models. The inlet concentration of both metal ions was directly related to the 50% breakthrough time. The obtained data indicated a high opportunity of Inshas area to meet the requirements posed by the International Atomic Energy Agency for shallow disposal.

Performance evaluation of hematite oxygen carriers in high purity hydrogen generation from cooking oil by chemical looping reaction

Chemical Looping Reforming (CLR) of cooking oil combining with Chemical Looping Hydrogen (CLH) for synthesis gas and high purity hydrogen production was performed with different hematite oxygen carriers. Results revealed the sample with higher content of Fe2O3 and ZnO displayed better reactivity. Zn2+ in hematite can promote the releasing of active lattice oxygen [O·] to improve carbon conversion efficiency and atomic selectivity based on metal synergistic effect. The highest carbon conversion efficiency 47.36% with H2/CO ratio closed to 2 and syngas yield 1.19 L/g were achieved in CLR stage. Accordingly, the maximum H2 concentration of 93.8% and yield of 444.3 ml/g were obtained in the subsequent CLH stage. It was revealed that the reduction of Fe species in oxygen carrier was a stepwise process in order of Fe3+→Fe2+→Fe0 in CLR reaction, whereas, the lattice oxygen O2− diffused outward from bulk to surface of oxygen carrier, transforming to chemical adsorption oxygen O2− and O− to participate reactions. The hematite oxygen carriers displayed irregularly blocky and porous structure. Meanwhile, sintering phenomena was not observed in the used samples. The BET surface area of oxygen carrier in four reaction stages increased from 1.727 to 2.703 m2/g.

Iron oxide colouring of highly-translucent 3Y-TZP ceramics for dental restorations

The influence of 0.01–2 mol% Fe2O3 powder addition on the microstructure, mechanical and optical properties, and hydrothermal stability of highly-translucent 3Y-TZP ceramics is assessed and compared with commercially available co-precipitated 0.18 mol% Fe2O3 doped ZrO2 powder-based ceramics. Only those ceramics with up to 0.1 mol% Fe2O3 resulted in a proper shade for dental zirconia ceramics, with a typical composition of 87 vol% t-ZrO2 and 13 vol% c-ZrO2. The amount of cubic phase increased at higher Fe2O3 content. The hardness (∼13 GPa) and fracture toughness (∼3.6 MPa m1/2) of the 0.01 mol% - 0.1 mol% Fe2O3 doped 3Y-TZP was comparable, whereas the hardness decreased above 0.5 mol% Fe2O3 and the fracture toughness decreased above 2 mol% Fe2O3. The hydrothermal ageing resistance slightly increased for Fe2O3 concentrations up to 1 mol%, whereas the translucency slightly decreased with increasing Fe2O3 content.

Mineralogy and geochemical features of Foumban clay deposits (west Cameroon): genesis and potential applications

ABSTRACTFive clay deposits in Foumban, west Cameroon, were studied for their morphological, mineralogical and geochemical properties to determine their suitability for ceramics. The clays were examined with X-ray diffraction, X-ray fluorescence, thermal gravimetric analysis and Fourier-transform infrared spectroscopy. Field studies showed that a homogeneous clayey layer occurs at the upper part of the laterite cover of the interfluves, while the valleys are occupied by a clayey heterogeneous hydromorphic material. The clays are composed of kaolinite, illite, smectite and chlorite, associated with quartz, K-feldspars, plagioclase, goethite, traces of rutile and hematite. Geochemical analyses of these samples show a relatively large amount of SiO2(45–71%), Al2O3(14–31%) and relatively little Fe2O3(up to 11%), suggesting weathering of mainly granitic and rhyolitic parent rocks. The majority of these clays may be used in the production of structural ceramics such as bricks (refractory or not) and tiles. The relatively high proportion of the alkalis (K2O + Na2O; 6–8%) in some samples from Marom and Njindare areas might be responsible for the low firing temperatures. The abundance of smectite limits the application of some Koutaba and Marom clays for structural ceramics, while the high Fe2O3contents (>8%) in some Bangourain clays indicate that some pre-treatment might be necessary prior to use.

The Neoproterozoic volcanic complex of the Boumalne inlier (Saghro massif, Eastern Anti-Atlas; Morocco): petrological and geochemical characteristics

Neoproterozoic volcanic series are exposed in the northern edge of the Saghro massif (Eastern Anti-Atlas, Morocco). Four volcanic rock types (basalt, andesite, dacite, and rhyolite) were distinguished in the Boumalne inlier within the so-called Saghro volcanic sequences based on petrographic and geochemical observations. Boumalne volcanic rocks contain high Al2O3, Fe2O3, Ba, Sr, Zr, Rb, and Nb contents, including calc-alkaline affinity in composition. Boumalne volcanic rocks are similar to other lower-Neoproterozoic volcanic rocks such Agouiniy formation in Sirwa inlier and in other parts of Bou-Azzer inlier. Indeed, they indicate an active subduction signature. The geochemical data show a LREE enrichment compared to HREE. The fractional crystallization has played a major role during the evolution of the magma. The less-siliceous dacitic rocks could have been formed after a low degree of partial melting of mafic parental magma source, whereas the rich-siliceous rhyolite may have been derived from dacitic magma source by a higher degree of fractional crystallization.

Influence of Structure and Mineral Association of Tuyere-Level Coke on Gasification Process

The gasification properties of feed coke and tuyere coke were investigated by non-isothermal thermogravimetric method under CO2 atmosphere. The physical and chemical structure features were also systematically tested, as well as the mineral composition. The pore characteristics, graphitization degree of carbon matrix, and ash content were the main factors determining the reactivity of coke. Higher L (c) decreases the reactivity of tuyere coke in low temperature, while larger porosity increases the reactivity in high temperature, forming an intersection with the gasification process of the feed coke. The high content of Fe2O3 in 25 to 20 mm tuyere coke made a rapid gasification reaction. The SiC produced in the tuyere area increased the porosity of coke especially the 5 to 1 mm coke at the edge of BF, which promoted the gasification process of coke in the area.

Geochemical Characterization of Bauxite Deposits from the Abruzzi Mining District (Italy)

The Abruzzi bauxite district includes the deposits located on the Campo Felice plateau and those of the Monti d’Ocre, which had been mined in the first part of the 20th century. Bauxite is of the karst type, with textures ranging between oolitic and oolitic-conglomeratic, the latter suggesting a partial reworking of evolved lateritic soils. The high contents of Al2O3 and Fe2O3 (average values 53.76 and 21.76 wt %, respectively) are associated with the presence of boehmite, hematite, and minor goethite. SiO2 and TiO2 have average values of 7.79 and 2.75 wt %, corresponding to the presence of kaolinite, anatase and rutile. Among the minor so-called “bauxitophile” elements V, Co, Ni, Cr and Zr, the most enriched is Cr, with an average value of 0.07 wt %. Nickel has an average value of 210.83 ppm. Vanadium shows an average value of 266.57 ppm, whereas the average Co concentration is 35.89 ppm. The total rare earth elements (REE) concentration in the sampled bauxite sites is variable between ca. 700 and 550 ppm. Among REEs, the most abundant element is Ce, with Ce anomalies commonly associated with authigenic REE-fluoro-carbonates, probably produced after the REEs remobilization from primary detrital minerals and their precipitation in neo-formed phases during the bauxitization process. Scandium and Ga occur in small amounts (57 and 60 ppm, respectively), but geochemical proxies of their remobilization and uptake in neo-formed minerals (Fe- and Al-(hydr)oxides, respectively) have been observed. The mean Eu/Eu* and Al2O3/TiO2 ratios and the Ni-Cr contents of the Abruzzi bauxites suggest that the parent rock of these deposits was a material of acid affinity, likely corresponding to volcanic tephra or eolic loess-type sands.

Effects of Fe2O3 addition and annealing on the mechanical and dissolution properties of MgO-and CaO-containing phosphate glass fibres for bio-applications

Abstract This paper investigated the preparation of phosphate glass fibres (PGFs) in the following systems: i) 45P2O5-5B2O3-5Na2O-(29-x)CaO-16MgO-(x)Fe2O3 and ii) 45P2O5-5B2O3-5Na2O-24CaO-(21-x)MgO-(x)Fe2O3 (where x = 5, 8 and 11 mol%) for biomedical applications. Continuous fibres of 23 ± 1 μm diameter were prepared via a meltdraw spinning process. Compositions with higher Fe2O3 content and higher MgO/CaO ratio required higher melting temperature and longer heating time to achieve glass melts for fibre pulling. The effects of Fe2O3 addition and annealing treatment on mechanical properties and degradation behaviours were also investigated. Adding Fe2O3 was found to increase the tensile strength from 523 ± 63 (Ca-Fe5) to 680 ± 75 MPa (Ca-Fe11), improve the tensile modulus from72 ± 4 (Ca-Fe5) to 78 ± 3 GPa (Ca-Fe11) and decrease the degradation rate from 4.0 (Mg-Fe5) to 1.9 × 10−6 kg m−2 s−1 (Mg-Fe11). The annealing process reduced the fibre tensile strength by 46% (Ca-Fe5), increased the modulus by 19.6%(Ca-Fe8) and decreased the degradation rate by 89.5% (Mg-Fe11) in comparison to the corresponding as drawn fibres. Additionally, the annealing process also impeded the formation of precipitate shells and revealed coexistence of the precipitation and the pitting corrosion as fibre degradation behaviours.

Petrography, lithostratigraphy and major element geochemistry of Mesoarchean metamorphosed banded iron formation-hosted Nkout iron ore deposit, north western Congo craton, Central West Africa

The Nkout banded iron formation (BIF) or iron deposit is located in the northwestern margin of the Congo Craton (CC) and is hosted within high-grade metamorphic Ntem complex. It is mainly made up of metamorphosed banded iron formations with resource estimation of 1.8 Bt @ 32.6% Fe indicated, and 0.9 Bt @ 30.3% Fe inferred. Nkout iron deposit is subdivided into three prospects namely East, Centre and West deposits. Results from lithostratigraphic studies allow detailed correlations between units in the Nkout succession. The litho-package from the top to the base stratigraphy comprises iron-rich member and the gneissic member. The first member forms the upper and middle units while the second member forms the lower unit and represents the footwall of the deposit. The upper unit is ∼200 m deep and consists of oxidized (hematite) and un-oxidized (fresh metamorphosed BIF) ore types. The middle unit is approximately 150 m thick and consists of fresh metamorphosed BIF with minor intercalation of biotite gneiss. The lower unit is made up of garnet-magnetite micaschist, biotite gneiss and pyroxene-biotite gneiss.The Nkout banded iron formation belongs to oxide facies magnetite-rich type which has suffered greenschist to amphibolite facies metamorphism, leading to recrystallization of chlorite, amphibole and garnet minerals. Its overall major oxide bulk chemistry is very similar to that of most Archaean iron-formations worldwide, with high SiO2 and Fe2O3 contents. However, the garnet-rich BIF has higher contents of Al2O3 (8.73 wt%), TiO2 (0.27 wt%), K2O (2.37 wt%) relative to magnetite-rich BIF, suggesting clastic contamination, thus a depositional environment closer to the continent. Furthermore, the absence of carbonate facies BIF in the entire Nkout deposit suggests deep water distal depositional setting, in an area of little or no organic carbon supplies.The lithostratigraphic correlation of metamorphosed BIF unit reveals both thicknesses and depth variations from West to the East, inferring a folded structure for the Nkout deposit. However the occurrence of BIF units in the entire deposit supports the fact that BIF deposition took place on a basin-wide scale. Considering the extent of the Ntem basin, it is suggested that a huge amount of Fe2+ in sea water was required. Thus, the deposition of Nkout BIF probably involved an iron rich environment of reduced Fe2+ rich hydrothermal fluid in chemically stratified sea water, similar to the depositional model proposed for the Minas BIF Supergroup of Quadrilátero Ferrífero in Brazil.

Maghemite quantification and magnetic signature of Brazilian soils with contrasting parent materials

Maghemite (Mh) is a ferrimagnetic mineral that governs magnetism in the clay fraction, especially in well weathered soils from tropical and subtropical regions. In this work, we assessed different methods for Mh quantification [1: area of the reflections obtained by X-ray diffraction (XRD) (standard method); 2: Rietveld refinement; 3: selective dissolution with H2SO4 and; 4: magnetic susceptibility (χ)] by application to Brazilian soils with contrasting parent materials (itabirite, basalt, gabbro, tuffite, gneiss and amphibolite). The methods based on H2SO4 dissolution were found to overestimate the Mh content with respect to the standard method based on X-ray diffraction. This was particularly so with samples from gneiss and amphibolite and samples with higher contents in poorly crystalline Fe oxides. Mh contents based on magnetic susceptibility measurements or the XRD-Rietveld refinement were closer to those provided by the standard method. Mh was found to accumulate in well weathered soils and soils with a high Fe2O3 content. Exception were soils from tuffite, which had high Fe2O3 contents (~330 g kg−1), exhibited low Mh levels (~5.5 g kg−1). Irrespective of the parent material, Mh particles typically fall in a single domain magnetic behavior; however, they can also acquire multidomain characteristics, probably as a result of isomorphic substitution and aggregation with hematite.

Geochronological and geochemical studies of the OIB-type Baiyanghe dolerites: implications for the existence of a mantle plume in northern West Junggar (NW China)

AbstractIn this paper, zircon U–Pb geochronology, major and trace elements, and Sr–Nd isotope geochemistry of the Baiyanghe dolerites in northern West Junggar of NW China are presented. The U–Pb dating of zircons from the dolerites yielded ages of 272.2±4 Ma and 276.7±6.2 Ma, which indicate the emplacement times. The dolerites are characterized by minor variations in SiO2(46.89 to 49.07 wt%), high contents of Al2O3(13.60 to 13.92 wt%) and total Fe2O3(11.14 to 11.70 wt%), and low contents of MgO (2.67 to 3.64 wt%) and total alkalis (Na2O+K2O, 5.1 to 5.97 wt%, K2O/Na2O = 0.37–0.94), which indicate affinities to metaluminous tholeiite basalt. The REE pattern ((La/Sm)N= 2.25–2.34, (La/Yb)N= 7.42–8.36), V–Ti/1000 and 50*Zr–Ti/50–Sm discrimination diagrams show that these rocks are OIB-type. The high contents of Zr and Ti indicate a within-plate tectonic setting, and samples plot in the ‘plume source’ field shown on the Dy/Yb(N)versus Ce/Yb(N)diagram. The positive εNd(t) values (+7.09 to +7.48), high initial87Sr/86Sr ratios (0.70442 to 0.70682) and depletions of Nb and Ta elements in the samples can be explained by the involvement of subducted sediments. In summary, it is possible that the Baiyanghe dolerites were derived from an OIB-like mantle source and associated with a mantle plume tectonic setting. Therefore, our samples provide the youngest evidence for the existence of a mantle plume, which may provide new insights into the Late Palaeozoic tectonic setting of West Junggar.