Natural Phosphate Minerals Research Articles

Highly variable content of fluorapatite-hosted CO32−in the Upper Cretaceous/Paleogene phosphorites (Morocco) and implications for paleodepositional conditions

Phosphorus (P) usually occurs as microcrystalline minerals of carbonate fluorapatite (CFA) in sediments of upwelling-related areas. The Upper Cretaceous/Paleogene marine sedimentary rocks in Morocco host the world's largest economic reserves in phosphorus, which were deposited on the eastern passive margin of the central Atlantic Ocean. However, a full petrographic, mineralogical and geochemical characterization of the Moroccan phosphate minerals is yet to be determined. Here, we use optical and scanning electron microscopies, X-ray diffraction, and infrared spectroscopy, in combination with a microprobe analyzer to document carbonate (CO32−) substitutions in CFA from two distinct phosphate basins and their possible implications for paleoenvironmental conditions. The Moroccan phosphorus-rich deposits predominantly comprise porous phosphatic peloids and coated grains with a maximum size of 500 μm, which in turn consist of high-density nano- to micron-sized rod-shaped and sphere-like crystallites. Bulk and in situ analyses reveal heterogeneous CO32−content in CFA at the regional- and grain-scale. Fourier transform infrared spectra indicate that CO32−accommodates only in the phosphate site within the fluorapatite structure, as found in other natural phosphate minerals. Bulk CO32−variations in CFA between phosphate basins, ranging from 1.97 to 8.24%, are likely related to depositional conditions – and thus of supersaturation with respect to CFA – during mineral formation, transport, and redeposition. Moreover, some phosphatic coated grains have revealed alternations of CO32−-rich and CO32−-poor CFA laminae, pointing out local differences in CO32−concentrations in sediment pore waters. Interestingly, the change in shape and diminution in size of CFA crystallites caused by high content of CFA-hosted CO32−could have possibly increased the intragranular porosity, highlighting an underestimated role of CO32−on grain morphology. Considering the higher solubility of CO32−-rich CFA than fluorapatite, the application of such phosphate rocks from specific Moroccan areas as rock phosphate powders may be of deep interest for long-term soil fertilization. These results further evidence the importance of studying phosphorites for economic, environmental, and scientific interests.

Photocatalytic degradation of emerging antibiotic pollutants in waters by TiO2/Hydroxyapatite nanocomposite materials

TiO2-hydroxyapatite nanocomposites were prepared by the simultaneous gelation of titanium alkoxide and precipitation of a re-dissolved natural phosphate mineral in ammonia and tested for drug degradation in solution under UV light. Pharmaceuticals were preferentially adsorbed on the apatite-rich composites, whereas their photodegradation was more effective in the TiO2-rich phases. At high TiO2 content, the efficiency of photocatalytic degradation of nanocomposites is better compared to that of TiO2related to the antibiotic affinity. Using 40TiHAp as photocatalyst, ciprofloxacin and ofloxacin were 100% photodegraded within 15 min and 120 min, respectively. The proposed nanocomposites are efficient catalysts for the enhanced adsorption and photocatalytic degradation of ciprofloxacin and ofloxacin in water.

Elaboration and characterization of new phosphate glasses based on natural phosphate and red clay: influence of the chemical composition on the chemical durability

New phosphate glass formulations based on Moroccan natural phosphate minerals alone or with Moroccan red clay additive (containing the P2O5-SiO2-CaO-Al2O3-MgO-Fe2O3-K2O-Na2O-TiO2 complex) have been successfully prepared by the quenching method. The chemical composition of each of the elaborated phosphate glasses was determined by X-ray fluorescence analysis (XRF). These investigated phosphate glasses have an excellent homogeneity as was verified by SEM. Their amorphous behavior was confirmed by XRD and DSC. The increase in density and glass transition temperature due to the addition of clay is believed to be related to the crosslinking of the phosphate chains. Structural investigation of these phosphate glasses was carried out using FTIR and Raman spectroscopies. The results obtained show that the composition of these glasses contains a mixture of ultraphosphate and polyphosphate structural units. The concentrations of this mixture depending on the initial composition of the glass components. A correlation between the chemical composition and the chemical durability of the investigated glasses was studied. The results showed that the dissolution rate of the glasses decreases by increasing the clay composition up to a point. This can be explained by assuming the formation of oxygen bridges and strong bonds within the various glasses.

Magnesium Potassium Phosphate Compound for Immobilization of Radioactive Waste Containing Actinide and Rare Earth Elements.

The problem of effective immobilization of liquid radioactive waste (LRW) is key to the successful development of nuclear energy. The possibility of using the magnesium potassium phosphate (MKP) compound for LRW immobilization on the example of nitric acid solutions containing actinides and rare earth elements (REE), including high level waste (HLW) surrogate solution, is considered in the research work. Under the study of phase composition and structure of the MKP compounds that is obtained by the XRD and SEM methods, it was established that the compounds are composed of crystalline phases—analogues of natural phosphate minerals (struvite, metaankoleite). The hydrolytic stability of the compounds was determined according to the semi-dynamic test GOST R 52126-2003. Low leaching rates of radionuclides from the compound are established, including a differential leaching rate of 239Pu and 241Am—3.5 × 10−7 and 5.3 × 10−7 g/(cm2∙day). As a result of the research work, it was concluded that the MKP compound is promising for LRW immobilization and can become an alternative material combining the advantages of easy implementation of the technology, like cementation and the high physical and chemical stability corresponding to a glass-like compound.

Vitrification and derived glass-ceramics from mining wastes containing vermiculite and lithium aluminium phosphate

The waste vitrification of abandoned open sky vermiculite deposits has been considered by combining with a natural phosphate mineral residue. Several batches haven been designed from the composition system: Li2O-MgO-Al2O3-P2O5-SiO2 including some Fe2O3 and Fluoride. The resulting glasses are transparent and smooth green coloured, giving rise after TTT treatments to several opal, opaque glass-ceramics with iridescent surface. Full characterization has been carried out by XRD and electron microscopy with EDS, as well as by XPS spectroscopies, concluding that the main crystalline phases formed were α-cordierite and β-spodumene. The surface of these glass-ceramics from vermiculite-amblygonite is enriched in Fe2O3. Compared to the parent glasses, the final glass-ceramics exhibited and improvement in fracture toughness.

Co11Li[(OH)5O][(PO3OH)(PO4)5], a Lithium-Stabilized, Mixed-Valent Cobalt(II,III) Hydroxide Phosphate Framework.

A new metastable phase, featuring a lithium-stabilized mixed-valence cobalt(II,III) hydroxide phosphate framework, Co11.0(1)Li1.0(2)[(OH)5O][(PO3OH)(PO4)5], corresponding to the simplified composition Co1.84(2)Li0.16(3)(OH)PO4, is prepared by hydrothermal synthesis. Because the pH-dependent formation of other phases such as Co3(OH)2(PO3OH)2 and olivine-type LiCoPO4 competes in the process, a pH value of 5.0 is crucial for obtaining a single-phase material. The crystals with dimensions of 15 μm × 30 μm exhibit a unique elongated triangular pyramid morphology with a lamellar fine structure. Powder X-ray diffraction experiments reveal that the phase is isostructural with the natural phosphate minerals holtedahlite and satterlyite, and crystallizes in the trigonal space group P31m (a = 11.2533(4) Å, c = 4.9940(2) Å, V = 547.70(3) Å3, Z = 1). The three-dimensional network structure is characterized by partially Li-substituted, octahedral [M2O8(OH)] (M = Co, Li) dimer units which form double chains that run along the [001] direction and are connected by [PO4] and [PO3(OH)] tetrahedra. Because no Li-free P31m-type Co2(OH)PO4 phase could be prepared, it can be assumed that the Li ions are crucial for the stabilization of the framework. Co L-edge X-ray absorption spectroscopy demonstrates that the cobalt ions adopt the oxidation states +2 and +3 and hence provides further evidence for the incorporation of Li in the charge-balanced framework. The presence of three independent hydroxyl groups is further confirmed by infrared spectroscopy. Magnetization measurements imply a paramagnetic to antiferromagnetic transition at around T = 25 K as well as a second transition at around 9-12 K with a ferromagnetic component below this temperature. The metastable character of the phase is demonstrated by thermogravimetric analysis and differential scanning calorimetry, which above 558 °C reveal a two-step decomposition to CoO, Co3(PO4)2, and olivine-type LiCoPO4 with release of water and oxygen.

Phosphorus fertilizer prepared from natural Burenkhaan phosphorite (Mongolia) by a mechanical activation

Phosphorus is one of the most important nutrients for plant growth. The main compounds containing phosphorus are natural phosphate minerals such as apatite. However, the solubility of apatite is low in the humic acid in soil. Therefore, phosphorus is applied as a fertilizer for plant growth. Generally, fluorapatite Ca5(PO4)3F is used for the preparation of phosphorus fertilizer such as superphosphate. Mongolia is rich in phosphorus reserves which are distributed between two phosphate basins at Khuvsgul (4.5 billion tonnes) and Zavkhan (1.2 billion tonnes). However, preparation of phosphorus fertilizer from natural fluorapatite, by a wet chemical method raises health and ecological concerns. Therefore, we have mechanically treated phosphorite from the Burenkhaan deposit in order to prepare fertilizer by a dry method. Phosphate samples were milled in a vibratory ball mill for 15–120 min. Raw and milled samples were characterized by XRD, FTIR, particle size analyzer and SEM. The efficacy of mechanical activation was determined by solubility of milled phosphate in a 2% citric acid solution. Mechanical activation results in a threefold increase in solubility of phosphorus in citric acid solution to 18%. Such solubility is comparable with the superphosphate prepared by the wet chemical method.

Porous hydroxyapatite-TiO2 nanocomposites from natural phosphates and their decolorization properties

Titanium dioxide-hydroxyapatite nanopowders were prepared by the simultaneous gelation of a titanium alkoxide and precipitation of a redisolved natural phosphate mineral. Evolution of the crystallinity, porous features and surface reactivity of these powders as a function of Ti content and heating was studied. Optimal conditions were found for the preparation of a low-cost nanocomposite powder that was as effective as pure titania for the decolorization of methylene blue solutions.

Hazardous industrial waste stabilization using inorganic phosphates: Investigation of possible mechanisms

Abstract The present study focuses on the use of phosphate-containing compounds, such as apatites, as stabilization additives for solid industrial wastes. The examined highly toxic waste contained mainly lead, iron, and bromides. Phosphates (synthetic or natural), when used as additives, were found to diminish the release of lead from the stabilized waste below the respective legislative concentration limits, following the application of DIN 38414 standard leaching method and within the range of pH values 7.5-10.5. The respective synthetic compounds of lead, PbO and Pb(OH)Br, existing also in the solid waste, were additionally studied during simulation experiments, in order to examine the possible mechanisms of waste stabilization, by using the same additives (phosphates). The obtained results showed the possibility of another parallel mechanism, different from that proposed in the literature, which is the sorption of aqueous lead ions onto the apatite surface. It was suggested that lead can be also transformed into the less soluble solid phases through the interaction (surface crystallization) of exposed lead surface with the aqueous environment. The formation of new crystals onto the surface of lead phase was sufficiently fast, especially in the case of natural phosphate mineral additive, most probably due to the presence of calcite, which supplies part of its carbonate content for the formation of respective lead carbonate solid phases.