Phosphatic Rocks Research Articles

Phosphorus recovery as struvite and hydroxyapatite from the liquid fraction of municipal sewage sludge with limited magnesium addition.

Phosphorus (P) is an essential element to produce feed and fertilizers but also a nonrenewable resource. Both the predicted exhaustion of phosphatic rocks and the risk of eutrophication lead to an increasing necessity for P recovery methodologies to be applied in municipal wastewater treatment plants (WWTPs). One of the most promising solutions involves the precipitation of P-based minerals reusable as slow-release fertilizers. In this study, P recovery as struvite and hydroxyapatite from a municipal WWTP digestate liquid fraction (centrate) was investigated at varying pH (8-10), reagent typologies (MgCl2 , NaOH, Ca(OH)2 , and CaCl2 ), and concentrations under limiting magnesium doses through liquid- and solid-phase analyses and thermodynamical modeling. A maximum P recovery of 87.3% was achieved at pH 9 by adding NaOH and MgCl2 at a dose of 656mg/L (the higher tested). According to these data, it was estimated that 92.0 tons/year of struvite and 33.2 tons/year of hydroxyapatite could be recovered from the WWTP centrate with a cost for reagent consumption being almost 50% of the mean P market value. An increase in P precipitation was observed while comparing experiments with the same pH values but with a higher Mg2+ dose. Ca2+ addition led to extensive P precipitation but mainly as amorphous phases that interfere with struvite formation.

Controls of REY enrichment in the early Cambrian phosphorites

Rare earth elements and Yttrium (REYs) are critical to the emerging high-tech and green-energy industries, generating tremendous REY demand in recent decades. Recently, many sedimentary phosphorites have been reported to have extraordinary REY enrichment (> 1000 ppm) and may become new REY resources. However, the controls of REY enrichment in phosphorites have not been well constrained. To better understand the discrepant REY enrichment in phosphorites, the early Cambrian high-REY Zhijin (ZJ) phosphorites (∼500–2000 ppm) and the relatively low-REY Meishucun (MSC, ∼200–400 ppm) and Xia’an (X’A, mostly < 200 ppm) phosphorites on the Yangtze Block of South China were investigated with mineralogy, bulk-rock elements, total organic carbon, in-situ elements, and Zn-Fe isotopes. The mineral characteristics, REY indexes, and in-situ REY mapping indicate that the X’A phosphorites may represent pristine phosphorites, whereas the ZJ and MSC phosphorites may have experienced intensive diagenetic alteration. Diagenetic alteration can only explain the REY enrichment in the MSC phosphorites compared to the pristine X’A phosphorites, but it does not sufficiently explain the extraordinary REY enrichment in the ZJ phosphorites. Additionally, the lower δ66Zn values of the ZJ and X’A phosphorites (δ66Znaverage = 0.16‰ and 0.14‰, respectively) than those of the MSC phosphorites (δ66Znaverage = 0.75‰) indicate higher productivity levels in the ZJ and X’A areas. However, the high-productivity X’A phosphorites yielded very low REY concentrations, indicating that the extraordinary REY enrichment in the ZJ phosphorites cannot be ascribed to high productivity levels. Notably, the ZJ phosphorites may have experienced more intensive Fe redox cycling under fluctuating oxic–suboxic deposition conditions (∼0.0‰–0.45‰ δ56Fe values in near-pure phosphorites) than the MSC and X’A phosphorites with completely oxic deposition conditions (∼0.0‰ δ56Fe values). Frequent Fe redox cycling can greatly enrich REYs in porewater, which can be subsequently transferred into francolites during its formation and early diagenesis. Therefore, frequent Fe redox cycling driven by fluctuating oxic–suboxic seawater conditions may be responsible for the extraordinary REY enrichment in the ZJ phosphorites. If this is the case, we propose that phosphorites deposited near the oxic–suboxic redox chemocline are favorable for extraordinary REY enrichment, such as the coeval near-slope phosphate concretions on the Yangtze Block and other phosphorites or phosphatic rocks formed in different basins at different geological times.

Mineralogy, geochemistry and origin of the phosphorites at Um El-Huwtat mine, Quseir, Central Eastern Desert, Egypt

X-Ray diffraction results for the study mine are mainly represented by two phases (phosphatic and non-phosphatic). First phase is represented by apatite (fluorapatite) which is the dominant. The second phase includes carbonate minerals; calcite, dolomite, evaporated mineral (gypsum), sulphide mineral (pyrite), in addition to quartz as a silicate mineral. These results are confirmed by the petrographic study. The detailed microscopic examinations indicate that the phosphorites at the study mine is essentially composed of phosphatic lithoclasts (mainly collophane), phosphatic bioclasts (bone fragments, spines and teeth of vertebrates such as shark fish as well as coprolites), opaques, and quartz embedded in a microcrystalline phosphatic matrix (contains some of dahllite) associated with a microcrystalline quartz according to their decreasing order of abundance. The paragenetic sequence of the studied phosphorites is as follows: fluorapatite, collophane then followed by dahllite. The redox-sensitive trace elements, its ratios, authigenic uranium as well as Fe/Ti can be signifying the redox conditions. Also, they revealed that the study rocks are deposited under the oxic to anoxic environment coupled with hydrothermal solution. The trace and rare earth elements are generally associated with phosphatic rocks. Thus, the phosphatic rocks of Um El-Huwtat mine, Quseir can be considered as sources of trace and rare earth elements. Also, pyrite can be considered as another possible source for REEs. The studied phosphatic rocks characterized by light REE (LREE = 69 ppm) enrichment than heavy REE (HREE = 25 ppm). All the recoded values of the heavy metals for the study mine are higher than those in Tunisia (400.3 ppm), Morocco (571.75 ppm) and Jordan (187 ppm). The post-depositional conditions are responsible for the enrichment of U and Th and/or intensive chemical weathering in Quseir area. Enrichment Factor (EF) indicated that the enrichment or deletion of the elements may be a function of that association and the origins of the various phosphate fractions. The studied phosphatic rocks are suitable for industrialized fertilizers according to the world guides.

REE enrichment of phosphorites: An example of the Cambrian Georgina Basin of Australia

Phosphate-rich sedimentary rocks (phosphorites) host significant concentrations of rare earth elements (REE, including Y) that are critical for development of ‘green’ technologies and renewable energy supply. Cambrian (ca. 505 Ma) phosphorites from the epicontinental Georgina Basin can contain up to 0.5 wt% REE, marking them as among the most REE-enriched phosphorites globally. This contrasts with previous work that proposed generally poor REE endowment of Cambrian phosphorites across the world. Here, we report orders of magnitude variation in REE concentration across the northern, central and southern parts of the Georgina Basin. We use principal component analysis (PCA) on centred-log ratio (CLR) transformed whole rock geochemical data to show that the southern phosphate prospects of the basin (Ardmore, Duchess, Phosphate Hill) have higher concentrations of elements that substitute into the major primary phosphate mineral carbonate fluorapatite (CFA) (P2O5, CaO, Na2O, REE, Sr and possibly Ba), while those of the central and northern prospects (Lily and Sherrin Creek, Barr Creek, DTREE, Paradise South and Paradise North) show a greater contribution of terrigenous material characterised by a higher concentrations of elements typically excluded from the CFA lattice (SiO2, TiO2, Al2O3, K2O, MgO, Zr, Nb, Cs, Ga and Rb). REE concentrations are up to two orders of magnitude higher in the southern prospects than in the central and northern prospects, while phosphorites from all prospects display modern seawater-like REE patterns.It is unlikely that global secular changes of seawater chemistry through time are the dominant control on the REE content of the Georgina Basin phosphorites, given the relative short time span of phosphogenesis (ca. <5 m.y.), the restricted interaction of the epicontinental and open sea waters, and the order of magnitude variations in REE concentration on a localised basin scale. Instead, variations in REE concentrations across the Basin are likely due to: 1) textural differences, with apatitic non-pelletal mudstones dominating the northern and central prospects, and largely pelletal (granular) phosphorites in the south; 2) local seawater composition that reflected the proximal basement rocks and riverine/groundwater input. Higher concentrations of REE in the southern prospects may be explained by surface and groundwater interaction with A-type granite and schistose metasedimentary basement rocks. We suggest, therefore that REE prospectivity of phosphatic sedimentary rocks is not primarily controlled by temporal variations in global seawater chemistry, but rather by local sedimentological and source region factors.

Successful spectral remote sensing techniques for mapping apatite mineral of phosphatic rocks at eastern side of Abu Tartur Plateau, Western Desert, Egypt

Successful spectral remote sensing techniques for mapping apatite mineral of phosphatic rocks at eastern side of Abu Tartur Plateau, Western Desert, Egypt

Uranium–lead phosphate chronostratigraphy: A proof of concept from the mid-Carboniferous boundary

Sedimentary phosphates, chiefly composed of apatite group minerals, contain exceptionally high concentrations (10–200 ppm) of U relative to other sedimentary precipitates, making them an attractive target for U–Pb dating. Phosphate-rich sedimentary rocks are common from the Neoproterozoic onwards and commonly occur at key points in the geological record, often coinciding with periods of significant environmental flux or facies change. There is thus a clear rationale for dating phosphatic rocks. In this study, we demonstrate how spatially-resolved U–Pb dating of sedimentary apatite by laser-ablation quadrupole inductively-coupled-plasma mass-spectrometry (LA-Q-ICPMS) can provide constraints on early phosphate diagenesis and reworking in ancient rocks. Our samples are from two locations in a well-characterized stratigraphic sequence containing phosphorites, and phosphate-rich carbonates and shales in western Ireland, which span the Mississippian–Pennsylvanian (mid-Carboniferous) boundary. Sedimentary phosphate preserves precise (<0.7% uncertainty) U–Pb ages that record early diagenesis, or sediment reworking, depending upon the facies sampled. These ages are consistent with age constraints derived from Carboniferous conodont biostratigraphy from the same sections. Phosphorite deposition, occurring on the sediment-starved margin of an epeiric basin, is constrained by U–Pb dating of apatite to the lower part of the Bashkirian stage at 320.7 ± 2.0 Ma (MSWD = 1). However, we identify a significant time-gap between the phosphorite and the immediately underlying carbonate stratigraphy, and thus attribute phosphorite accumulation to forced regression accompanying a widely recognized and significant glacial advance in Gondwana that took place at the mid-Carboniferous boundary. Our two sampling sites are several kilometers apart, broadly along strike of the basin margin, but preserve U–Pb isotopic and trace element compositional information that is strikingly consistent at the same stratigraphic levels. If used appropriately, integrated phosphate U–Pb dating and trace element analysis could provide age constraints for key parts of the Neoproterozoic and Phanerozoic, aiding reconstruction of evolutionary and paleoenvironmental records.

CARACTERIZAÇÃO DO ALVO FOSFÁTICO DE BOCAINA, PORÇÃO LESTE DA BACIA DO PARNAÍBA: SISTEMÁTICA INTEGRADA DE FÁCIES SEDIMENTARES, MINERALOGIA, GEOQUÍMICA E ESPECTROSCOPIA DE REFLECTÂNCIA

Ocorrências de fosfato sedimentar na porção leste da Bacia do Parnaíba são conhecidas desde a década de 70 por pesquisas realizadas pela CPRM e DNPM. Os alvos fosfáticos estão concentrados na sequência devoniana, mais especificamente em rochas da Formação Pimenteiras. Devido a demanda pelo detalhamento e descoberta de novos alvos na região de Bocaina, este trabalho tem como objetivo a caracterização sedimentológica, e espectral das rochas associadas a anomalias fosfáticas da Formação Pimenteiras utilizando técnicas de difratometria de raios-X, fluorescência de de raios-X portátil e espectroscopia de reflectância. As rochas foram individualizadas em quatro fácies sedimentares: Sm (arenito maciço), Sp (arenito plano-paralelo), Fm (finos maciços) e Fl (finos laminados) que indicam um ambiente deltaico distal evoluindo para uma plataforma em um trato de sistema transgressivo. Anomalias de fósforo (&gt;450ppm) estão associados a níveis fosfáticos reconhecidos entre as unidades. Por análises de DRX, carbonato-hidroxapatita é a principal fase fosfática encontrada na área de estudo e caolinita, ilita, esmectita são os principais filossilicatos identificados. As análises por espectroscopia de reflectância possibilitaram a individualizaçãos das quatro fácies e sugerem que caolinita, ilita e goetita podem ser utilizados como endmembers em futuros mapeamentos espectrais na região.&#x0D; &#x0D; Palavras-chave: Bacia do Parnaíba, Fosfato, Formação Pimenteira, Fácies Sedimentares.

Discovery of spherulitic dahllite associated with carbonates at Hamadat phosphorite mine, Qusseir, Central Eastern Desert, Egypt

Microscopical and mineralogical studies reveal first recorded spherulitic dahllite (3Ca 3 (PO4)2 Ca CO3) in the phosphorite rocks associated with carbonate rocks of Hamadat Mines (Duwi Formation) at Qusier area, Central Eastern Desert, Egypt. Mineralogically, the phosphatic rocks of Hamadat Mines are mainly consisting of fluor-apatite, dahllite, dolomite, calcite, quartz and pyrite. Petrographically, the studied dahllite in Hamadat Mines are authigenic in origin. Genetically, spherulitic dahllite at Hamadat Mines (Duwi Formation) in Qusier area is resulting from diagenesis processes; dolomitization and the re-crystallization process. Geochemical analysis of trace, rare earth elements and the petrogaphical is indicated that the phosphatic rocks are deposited under oxic to anoxic condition. Dolomitization process plays an important role in the concentration of trace and rare earth elements in the phosphatic rocks at Hamadat Mine. Dahllite layer has a relatively higher content in most of rare earth and some of the trace elements than those in the phosphate layer, which reveal that dahllite structure may be having the ability to scavenging them than the phosphatic construction. The chemical index of alteration (CIA), trace elements and La/Ce ratios pointed out that these phosphatic rocks were of hydrogenous origin deposited in cold and dry climate during low weathering. Finally, the hydroxial-apatite can be prepared to be used as a natural row material in the biological industry according to the chemical composition.

Enhanced-Efficiency Phosphorous Fertilizer Impacts on Corn and Common Bean Crops and Soil Phosphorus Diffusion

Phosphorus (P) supply to crops is a major constraint on the quantity and quality of food production in tropical soils, which are often characterized by highly weathered soils having low phosphorus use efficiency. Increasing P fertilizer use efficiency is a good tool for increasing food production to feed an increasing world population. Enhanced efficiency P fertilizer is used to achieve this goal. The lack of information about soil P diffusive flux and corn and common bean yield response with increased efficiency P fertilizers justify studies to evaluate the performance of this type of fertilizer. The aims of this study were to evaluate P diffusive flux and corn and common bean crop response to P sources and rates. A laboratory trial was carried out to evaluate soil P diffusive flux in response to P sources (MAP and Policote coated MAP). Field trials were carried out to evaluate corn and common bean yields in response to P sources (MAP and Policote coated MAP) and rates. Policote, an additive based on water-soluble polymers, is an anionic copolymer with iron an aluminum affinity. Increasing contact time between P-fertilizers and soil reduced phosphorus diffusive flux. Policote coated P-fertilizer resulted in higher phosphorus diffusion than conventional phosphorus fertilizer. Phosphorus fertilization increased corn and common bean yields. Policote coated phosphorus fertilizer resulted in higher agronomic P efficiency use, corn, and common bean yields than conventional phosphorus fertilizer. Policote coated P fertilizer can be used as an enhanced efficiency fertilizer and is a more efficient way to deliver required phosphorous to plants. Reducing farm investment, increasing agricultural profits, preserve phosphatic rocks reserves, and avoid the overuse of phosphate fertilizer could be realized through the rational use of enhanced efficiency fertilizers and fertilizer rate use reduction.

Chemostratigraphy of the Upper Cretaceous-Paleogene organic-rich succession on the southern Tethys margin in Egypt

During the Late Cretaceous-Paleogene time, a widespread sedimentary organic-rich succession developed throughout the middle latitudes of Egypt. Since the study area conserves the organic-rich intervals three shallow boreholes were drilled through the Upper Cretaceous-Paleogene succession on the southern Tethys margin of Egypt. This work employs complete unpublished inorganic and organic geochemical data of 368 metric core samples to construct the chemostratigraphic framework of the studied sedimentary sequence. The paleoenvironmental conditions that prevailed at the time of deposition were discussed. A total of 368 samples were analyzed for 52 major and trace elements by Inductively Coupled Plasma Mass Spectrometry and for organic carbon concentrations by LECO C230 combustion furnace.The statistical treatment suggested five influential controlling factors during the deposition of the studied sedimentary succession. These factors express the influence of the terrestrial controls, phosphorite, anoxia, argillaceous marine sediments and/or marine shale and earliest diagenesis, in descending order of their relative strength. According to the microscopic examination supported by the chemical composition of the major oxides, seven lithofacies were defined; carbonate (limestone), dolomitized rocks, argillaceous limestone (marlstone), calcareous shale, siltstone-mudstone, phosphorites, and phosphatic rocks. Moreover, the diagnostic trace element content of each geological formation was assessed. Some of the obtained geochemical features were adopted as reliable chemostratigraphic indicators and to discriminate among the different depositional environments of the studied sequence.

Alluvial nodular monazite in Monfortinho (Idanha-a-Nova, Portugal): Regional distribution and genesis

This work constitutes a contribution to the knowledge on the occurrence of nodular monazite in the Monfortinho (Idanha-a-Nova) alluviums and its genesis. A new edition of the alluvial nodular monazite regional distribution map is presented, underlining its wide occurrence and preferential concentration in the north-western and central zones of this region. The assessment of the geological and environmental evolution during Neoproterozoic-Palaeozoic and Caenozoic times and alluvial nodular monazite accumulation seems to provide a direct association between the presence of the Ordovician rocks, in particular the radioactive (carrying radioactive heavy minerals) quartzite (one of the most probable original sources) and Caenozoic sedimentary rocks (most probably the secondary source). Nevertheless, the Slate-Greywacke Complex cannot be excluded as a host rock for nodular monazite as well. Alluvial heavy mineral concentrates include: iron oxide/hydroxide, ilmenite, tourmaline, nodular monazite, monazite, xenotime, zircon, rutile, anatase, brookite, apatite, andalusite, gold, cassiterite and topaz. There is a significant REE enrichment in these concentrates (up to >32,000 mg/kg), mainly in LREE-MREE. The contents in Ce and Th, Th and REE and Ce and La showed good correlation (0.97, 0.96 and 0.99, respectively), reflecting mainly the striking presence of nodular monazite, as can be proved by the similarity among NASCN patterns of this mineral and concentrates. In Monfortinho there are two distinct alluvial nodular monazite populations: 1) distal pre-deformation nodules generation, from the central western area, mostly ellipsoidal to discoidal, with irregular not orientated probable detrital mineral inclusions; and 2) proximal generation, in the northern area near the Ordovician rocks, with smaller grains, with mostly irregular surfaces. Diagenetic/low metamorphic pre-deformation distal Monfortinho nodules population growth can be recognised and characterised by the encompassing of irregular unoriented mineral inclusions of the host matrix rock; preferential incorporation of MREE over other REE in the core nodules, consistent with diagenetic MREE-rich environmental/mineralized fluids supplied by the dehydration of Variscan sedimentary marine sequences with phosphatic rocks, at the start of nodule formation. The slight increase in Ca towards the nodule rims denotes a relative increase in fluid salinity during nodule growth, consistent with the ineffectiveness of metamorphic dewatering in dissolving the significant salt content of those marine sequence(s); Th increment in nodule rims points to the temperature increment at this stage; its moderately to pronouncedly negative Eu anomalies and the general involvement of the cheralitic substitution mechanism are characteristic of metamorphic monazites. Monfortinho and other published data suggest that in the beginning of nodular monazite formation the fractionation (La/Sm)N tended to be lower than that of the original source (detrital relic mineral/seawater), very similar to primary synsedimentary apatite or to monazite nodules interpreted to have precipitated directly from seawater. At the end the fractionation values can be substantially higher than those and may be dependent on the conditions established during the different geologic environments. The persistence of the ideal conditions (local P-T and fluid chemical composition evolution) to nodule growth, during Variscan diagenetic and metamorphic events, turned possible that Monfortinho monazite nodules record a relative high range of fractionation values [(La/Sm)N = 0.08 to10.40].

Isolation, occurrence, screening and characterization of rock phosphate solubilizing microbes

The present experiment is conducted on ‘isolation, Occurrence, Screening & Characterization of Rock phosphate solubilizing Microbes’. Phosphorus is the least mobile element in plant and soil contrary to other macronutrients. It precipitates in soil as orthophosphate or is absorbed by Fe and Al oxides through legend exchange. Phosphorus solubilizing bacteria play role in phosphorus nutrition by enhancing its availability to plants through release from inorganic and organic soil P pools by solubilization and mineralization Rock Phosphate is the cheapest and abundant Phosphatic fertilizer available but due to its sparse solubility. Most agricultural soils contain large reserves of phosphorus (P), a considerable part of which accumulates as a consequence of regular applications of P fertilizers. However, a greater part of soil phosphorus, approximately 95–99% is present in the form of insoluble phosphates and hence cannot be utilized by the plants combined application of rock phosphate with phosphate solubilizing microorganisms has emerged as a logical solution to this issue. The selection of microorganisms capable of solubilizing phosphorus (P) from rock phosphates (RP) may contribute to reduce the dependence of imported fertilizers in grain crops, reducing the costs of agricultural production, and also the environmental impacts. Principal mechanism in soil for mineral phosphate solubilization is lowering of soil pH by microbial production of organic acids and mineralization of organic P by acid phosphatase. Use of phosphorus solubilizing bacteria as inoculants increases P uptake. These bacteria also increase prospects of using phosphatic rocks in crop production. Greater efficiency of P solubilizing bacteria has been shown through co-inoculation with other beneficial bacteria and mycorrhiza In the present study bacterial and fungal strains were isolated from waste water, soil and sediment sample of ETP of Paradeep phosphate limited (PPL) and from Mahanadi river estuary (Paradeep), having potential to solubilize insoluble inorganic phosphates were characterized. Each isolates were tested for their tricalcium phosphate (TCP) and low grade rock phosphate (RP) solubilization efficiency in both solid and liquid medium. From the experiment it is found that out of 22 fungal isolates more than 50% were classified as efficient. There were significant differences in the availability of P among strains. From the Experiment it is also revealed that the solubilizing activity of both phosphates was associated with a reduction of pH which suggests that the acidification of the culture medium can be one of the mechanisms involved in the solubilization of P. Total number of 27 bacterial strains and 29fungal strains are taken for experiment and studied for maximum solubilization of insoluble inorganic phosphorous.. From the above study, it is concluded that More than 40% isolates of bacterial and fungal strains show the effect of phosphate solubilizing activity. The bacterial strain with 11B and fungal strain with 6F has highest phosphorous solubilization. From the maximum specific growth rate it can be concluded that the microbial isolates 6F and 11B are copiotrophs.

P2O5 – F- U Characterization and Depositional Environment of Phosphatic Rocks for the Duwi Formation, Qussier- Safaga Region, Red Sea Coast, Egypt.

Abstract The Duwi Formation in Qusseir-Safaga region is conformably overlain by the Qusseir variegated shales and underlain by the Dakhla shales. The studied phosphatic rocks in the Duwi Formation, is an attractive rock unit for it’s enrichment in heavy metals and U content. Mineralogically, phosphatic rocks in the Duwi Formation are mainly composed mainly of fluorapatite, in addition to minor occurrence of calcite, dolomite, gypsum, quartz, and pyrite. Geochemical data reveal that the rocks of the Duwi Formation were deposited under anoxic environments. The present study used the statistical result of the interrelation between P2O5, F and U concentrations on Egyptian phosphate samples and compared to the measured data. Uranium mostly occurs in an oxidized U 6+ state. It could be fixed with the phosphatic ion, forming secondary uranium phosphate minerals such as phosphuranylite and belovite in Qusseir region. In addition to Uranyl phosphates, uranium minerals in Safaga region contain also Uranyl carbonates and Uranyl sulfates, which had been attributed to the post-depositional U enrichment. The chemical data and index show that the phosphatic rocks in Safaga region are more enriched in the majority trace and rare earth elements, and are subjected to high chemical weathering than those in Qusseir region.

Structural and luminescent characterisation of uraniferous fluorapatite and haematite associated with phosphatic rocks of the Bijawar group in Sagar District, Madhya Pradesh (India)

The structural and spectroscopic characteristics of phosphatic ferruginous shale samples from the Bijawar Group rocks from Sagar District of Madhya Pradesh (India) have been probed for identification of uranium species. Fluorapatite (\(\hbox {Ca}_{5}\hbox {(PO}_{4})_{3}\hbox {F}\), FAP) and haematite (\(\upalpha \)-\(\hbox {Fe}_{2}\hbox {O}_{3}\)) were identified as the main phases in the separated mineral concentrates. The photoluminescence (PL) and X-ray absorption near edge spectroscopy (XANES) studies pointed to a strong experimental evidence of both U(IV) and U(VI) oxidation states in the mineral concentrate portion obtained from the same parent host rock. The PL spectrum has confirmed the charge transfer (f–d) transition bands in UV and near-UV regions with emission peaks at ca. 290, 313, 336, 399 and 416 nm, which has been attributed to the substitution of \(\hbox {Ca}^{2+}\) ions by U(IV) in FAP and broad structureless emission due to stabilisation of U(VI) as \(\hbox {UO}_{6}^{6-}\) in haematite. Time-resolved spectroscopy studies have revealed biexponential decay components lasting 2–5 ns for U(IV) species and \(10\,\upmu \hbox {s}\) for U(VI) species. These characterisations revealed the fundamental information about the oxidation state and form of uranium in this region. Remediation measures for the Bijawar region are also suggested.

Diagenetic evolution of the upper Devonian phosphorites, Alborz Mountain Range, northern Iran

The upper Devonian, mixed siliciclastic‑carbonate stratigraphic succession of the Geirud Formation in the Alborz Mountain Range, north of Iran, hosts numerous phosphorites and phosphatic rocks. These phosphorites, which represent one of the most globally important deposits in the Devonian, have gained little attention regarding their genesis and diagenetic evolution. This study focuses mainly on the post-depositional changes that occurred during shallow to deep burial diagenetic evolution and subaerial weathering of the Geirud phosphorites. The phosphorites consist of phosphatic massive mudclasts, detritus-rich lithoclasts, bioclasts and bones formed by several stages of phosphogenesis and erosion, reworking, winnowing and condensation associated with Famennian sea level changes. The phosphatic clasts consist of early diagenetic, poorly crystalline, carbonate fluorapatite (CFA) and pyrite cementing detrital quartz, illite, muscovite, rutile and zircon. Phosphatic clasts are intensely compacted with sutured grain contacts, along which dissolution and reprecipitation of chemically-refined, well crystalline CFA with a bright blue cathodoluminescence and illite occurred during deep burial diagenesis. Similarly, quartz shows deformation planar features; overgrowth cement was developed as a result of pressure dissolution in phosphatic sandstones, followed by precipitation of ferroan dolomite, ankerite and chlorite in secondary porosity. Subaerial weathering led to oxidation of pyrite and generation of acidic pH condition, under which Ca and P from phosphates, Fe and S from pyrite, Fe, Ca, Mg and Mn from ferroan carbonates and Al and Si from aluminosilicates were released to form goethite, psilomelane, calcite, gypsum and crandallite.The PAAS-normalized rare earth elements (REEs) show bell-shaped patterns with middle (REEs) enrichment, positive Eu anomaly and a weak negative Ce anomaly. This implies recrystallization of CFA in phosphorites and phosphatic rocks during deep burial diagenesis, deviating from the modern seawater-like REE patterns. In this regard, deep burial diagenesis affecting the upper Devonian Geirud phosphorites is possibly a common process in the Proterozoic-Paleozoic phosphorites in northern Iran and elsewhere in the world.

Lithologic characterization of the phosphorite-bearing Duwi Formation (Campanian), South Esna, West Nile Valley, Egypt

The Lower phosphatic member of the least Upper Cretaceous (Campanian) Duwi Formation, south Esna, at the western side of the Nile Valley is important rock unit for its relatively high enrichment of heavy metals and U content. The petrographic, mineralogical, and geochemical characteristics of the studied formation are determined using Polarizing Microscopy, X-ray diffractometry, and X-ray Fluorescence. Petrographically, the studied phosphatic grains are composed of phosphatic mudclasts and bioclasts embedded in varies matrix. Spherulitic dahllite, black opaque minerals, and framboidal pyrite are scattered in the matrix. Dahllite in the studied samples are authigenic in origin and formed as a secondary mineral by the re-crystallization of the original francolite. Esna Phosphatic rocks (Duwi Formation, Campanian) were deposited under reducing condition and were affected by chemical weathering. Mineralogically, they are composed of five mineral phases. Apatite (flour-apatite) and dahllite are the dominance; as well as, quartz, pyrite, and anhydrate. The studied phosphatic rocks samples are compared with the average of the Upper Continental Crust (UCC) and the Post-Archean Australian Shale. The trace and some rare earth element content: Mo, Cr, Sr, Co, La, and U are more enriched than those in the UCC. The trace elements in the study phosphatic rocks may be associated with each other or with the heavy minerals rather than with apatite. U contents in the study phosphatic rocks are associated with the heavy metals and trace elements during the chemical weathering under oxic conditions. The ratios Mo/Al and the high concentrations of the redox sensitive elements revealed that the studied phosphatic rocks were deposited under anoxic reducing marine environments coupled with hydrothermal solutions.

Occurrence of Carnotite in the Phosphatic horizon of the Sudr Chalk, Wadi El-Quseiyib, East Central Sinai, Egypt: Paleoenvironmental and Radioactivity Implications

Anomalous uranium contents were recognized in the phosphatic beds of the Campanian-Maastrichtian Sudr Chalk of Wadi El-Quseiyib at the East Central Sinai. Microscopic examination,and scanning electron microscopy revealed the presence of carnotite patches disseminated in thestudied Sudr Chalk phosphatic rocks. This mineral is recorded for the first time in the east centralSinai and it may be significant in discussing uranium prospection and the origin of secondary uraniumdeposits. The identification of this mineral directed the attention to study the natural radionuclidescontent which have been measured by gamma-ray spectrometry using a shielded HPGe detector. Thisstudy revealed that 238U and some of its progenies were redistributed after subjection to severalalteration processes.Petrographic study of Wadi El-Quseiyib phosphatic rocks revealed that they are consisted mainlyof collophane pellets, bone and teeth fragments, which were diagenetically cemented by calcite,gypsum and quartz materials. The studied phosphatic microfacies was described texturally aspelphospharudite and pelphospharenite. X-ray diffraction analysis proved the presence of carbonatefluorapatite (francolite) as the dominant phosphatic mineral, while calcite, gypsum and quartz are thedominant non-phosphatic minerals with minor contents of bassanite and jarosite and siderotil.Averages of P2O5 and uranium contents are 16.7 % and 70 ppm in the analyzed phosphatic rocks,respectively. Carnotite characteristics are identified by SEM/EDX in the studied phosphatic rockswhich indicate that the uranium is leached out from the phosphatic materials and re-deposited as finespecks in open pores by circulating meteoric water. The leached uranyl ions together with vanadateions are forming the identified carnotite under the influence of evaporation. The calculated annualeffective dose equivalent values (AEDE) are 0.478 and 0.504 mSv/yr for the lower and upperphosphatic beds, respectively. The calculated radium equivalent activity values of (Raeq) are 2319 and2802 Bq/kg for the lower and upper phosphatic beds, respectively. Accordingly, although theestimated (AEDE) to the public is below the recommended limits, but the equivalent radium activityand the expected coincided radon gas emanation renders the phosphatic exposures in the study areaclassified unsafe for prolonged public activities.

REEs geochemical characteristics of lower Cambrian phosphatic rocks in the Gorgan-Rasht Zone, northern Iran: Implications for diagenetic effects and depositional conditions

The phosphatic rocks in the Gorgan-Rasht structural Zone (north of Iran) are widely developed within the Soltanieh Formation of Upper Neoproterozoic-Lower Cambrian age. These rocks extend in length over 60 km, vary in thickness from 2.2 m to 5 m, and lie along the boundary of the Middle Dolomite and the Upper Shale members (Lower Cambrian) of the Soltanieh Formation. In this research, the geochemical characteristics of 16 phosphatic samples using rare earth elements (REEs) within a section in the Soltanieh Formation were investigated. The entire phosphatic samples show characteristically typical hat-shaped distribution patterns of REEs, strong negative Ce anomalies (Ce/Ce* = 0.30–0.51), and slightly positive Eu anomalies (Eu/Eu* = 1.34–1.73). The geochemical evidence such as hat-shaped distribution patterns, MREEs enrichment relative to LREEs and HREEs, and values of Er/Nd, Y/Ho, La/Nd, and (La/Yb)N ratios together with positive correlation between pairs of Eu/Eu*-Ce/Ce* and REEs-Ce/Ce* and negative correlation between pair of (Dy/Sm)N-Ce/Ce* reveal the important role of diagenetic processes in the distribution and concentration of REEs in the phosphatic rocks. This study demonstrated that the strong negative Ce anomalies and weak positive Eu anomalies are valuable indicators for determining redox conditions of diagenetic fluids existing during the development of the phosphatic rocks, and also suggest upwelling and mixing of organic-rich anoxic bottom seawaters with aerobic oxic seawaters before the development and progression of phosphatization processes in the depositional site. The geochemical parameters like Y/Ho ratio and strong positive correlation between REEs-TOC suggest that terrigenous materials along with organic matters were the principal source of REEs in the phosphatic rocks.

Rare earth element geochemistry of phosphatic rocks in Neoproterozoic Ediacaran Doushantuo Formation in Hushan Section from the Yangtze Gorges Area, South China

Phosphatic rocks are widely distributed in Neoproterozoic Ediacaran Doushantuo Formation in Yangtze Gorges Area, South China. In this study, rare earth element geochemistry of eight phosphatic rock samples from the Hushan Section has been studied. All the samples display typical hat-shaped REE patterns, moderate negative Ce anomalies (Ce/Ce*=0.55 to 0.67), slightly positive Eu anomalies (Eu/Eu*=1.05 to 1.22) and low Y/Ho ratios (38.2±5.6). The hat-shaped REE patterns indicate diagenetic alteration of the primary REE signatures, which coincides with detrital siliciclastic sources of REE based on the Y/Ho ratios. The degree of Negative Ce anomalies and positive Eu anomalies may have recorded the redox features of diagenetic fluids, suggesting an anoxic environment during the phosphogenesis processes in Neoproterozoic Ediacaran Doushantuo Formation, South China. The geochemical comparison between the Lower Phosphorite Layer and Upper Phosphorite Layer at Hushan indicates a greater degree of diagenesis occurred in the Upper Layer than the Lower one. Besides the terrigenous sources of REE, organic materials could have also played a role on the REE characteristics.

Rare earth element and Sr–Nd isotope geochemistry of phosphatic rocks in Neoproterozoic Ediacaran Doushantuo Formation in Zhangcunping section from western Hubei Province, South China

Phosphatic rocks are widely distributed in Neoproterozoic Ediacaran Doushantuo Formation in Yangtze Platform, South China. In this study, we examined samples from the Zhangcunping section in western Hubei Province with major element, rare earth element (REE) and Sr–Nd isotopic analyses on the phosphorites and the host dolostone rocks. We employed an acid-leaching method to separate the carbonate (acetic acid leachable) and phosphate (hydrochloric acid leachable) fractions in all the samples. The geochemical differences between the different fractions can be recognized based on the P2O5, REE contents and Sr–Nd isotopic characteristics. The carbonate fractions in the rocks display low total REE concentrations with seawater-like REE patterns, super-chondritic Y/Ho ratios, moderate negative Ce anomalies and positive Eu anomalies, indicating these carbonates have retained the signatures of paleo-seawater. On the contrary, the phosphate fractions display high total REE concentrations with hat-shaped REE patterns, generally lower Y/Ho ratios, weak negative Ce anomalies and positive Eu anomalies, which may have recorded the features of diagenetic fluids. Negative Ce anomalies and positive Eu anomalies displayed in the carbonate fractions of the studied samples may also indicate the anoxic environments of ocean basins in South China during the deposition of the Neoproterozoic Ediacaran Doushantuo Formation. A geochemical comparison between Lower Phosphorite Layer and Upper Phosphorite Layer indicates a greater degree of diagenesis occurred in the Lower Phosphorite Layer than the Upper Phosphorite Layer. The negative εNd(t) values of the samples suggest continental crustal sources for the REEs, and the lower values in the phosphorite samples (−6.9 to −6.0) than the dolostone samples (−5.5 to −3.8) may suggest different processes for them, and it is likely that the REEs in the phosphorites have been modified by diagenetic fluids with REE contributions of pore fluids derived from the clastic silicates in the strata which generally have lower εNd(t) values, whereas the dolostone took the REEs from the ambient seawater mainly.