Thermal investigations on phase transformations of Syrian phosphorite: Part I

The phase transformations of Syrian phosphorite upon mechanochemical activation are examined in the present work. The latter is carried out in planetary mill equipped with 20 mm steel milling bodies and duration from 30 to 300 min. The established by means of DTA, DTG, TG analyses transformation of non-activated carbonate fluorine apatite type B into the carbonate hydroxyl fluorine apatite (COHFAp) mixed type A2-B leads to substantial changes in the properties of the activated samples expressed in lowering the degree of crystallinity, strong defectiveness of the structure, and increase of the citric solubility. The thermal analysis gives evidence for the decomposition of the carbonate-containing component within the phosphorite, as from the positions placed in the vicinity of the hexagonal 6₃ axis (type A2), as well as from the positions of the phosphate ion (type B), and from the free carbonates. The data from the thermal analysis, the powder X-ray analysis and the infrared spectroscopy give also evidence for phase transformations of the activated apatite (with admixtures of quartz and calcite) into Ca₁₀FOH(PO₄)₆, β-Ca₃(PO₄)₂, Ca₄P₂O₉, Ca₃(PO₄)₂ · Ca₂SiO₄ and for that one of the quartz—into larnite and wollastonite. The influence of the α-quartz as a concomitant mineral is considered to be positive. The α-quartz forms Si–O–Si–OH bonds retaining humidity in the solid phase thus facilitating the isomorphous substitution OH⁻ → F⁻ with the subsequent formation of partially substituted COHFAp. Calcium silicophosphate and Ca₄P₂O₉ are obtained upon its further heating. The presented here results settle a perspective route for processing of low-grade phosphate raw materials by means of tribothermal treatment aiming at preparation of condensed phosphates suitable for application as slowly acting fertilizer components.     

Phase equilibria in the tricalcium phosphate-mixed calcium sodium (potassium) phosphate systems

Phase equilibria in the quasi-binary sections Ca₃(PO₄)₂-CaMPO₄ (M = Na, K) are distinguished by high-temperature isomorphism of glaserite-like phases α’-Ca₃(PO₄)₂ and α-CaMPO₄. The main differences of the Ca₃(PO₄)₂-CaKPO₄ system from the Ca₃(PO₄)₂-CaNaPO₄ system are a shift of invariant equilibria toward higher temperatures, deceleration of phase transformations, and the emergence of polymorphism of an intermediate phase of an ordered solid solution based on α-CaKPO₄. The low-temperature modification of this phase of a composition near Ca₈K₂(PO₄)₆ has the apatite structure with unoccupied hexagonal channels.     

Effect of high-energy milling and thermal treatment on the solid-phase reactions in apatite–ammonium sulphate system

The phosphorous fertilizers are a product of natural sedimentary phosphorite ores. Using this raw material to produce phosphoric acid and classic phosphorous fertilizers has generated well-known ecological problems. A new and perspective way to use the same materials is creating a new type of time-delayed fertilizers applying high-energy milling (HEM) activation method. The impact of the mechanical forces over the solids is mostly revealed through the changes of the quantities being related to the energetic stability and reactivity of the solid phase. The aim of this work is to report the results from the investigation on the chemical and thermal reactions in composites of natural apatite , which are HEM activated for different times and thermally treated, (from Tunisia) and ammonium sulphate. The Tunisian phosphorite belongs to the ‘basic’ apatites having a Ca/P ratio of 1.70–1.77 and is characterized by a complex mineral composition with major component carbonate-fluorapatite. The used ammonium sulphate—(NH₄)₂SO₄ is obtained as a by-product from cleaning industrial waste gases, using e-beam technology. The composites of Tunisian phosphorite ores and ammonium sulphate, mixed in a mass ratio 1:1, were HEM activated during 10 min to 50 h with 20 mm Fe-milling bodies and temperature treated up to 1,100 °C. As a result, the chemical properties of the treated composites changed. Proofs were found for (i) formation of new phases during HEM activation such as NH₄Ca(PO₃)₃ (NH₄)₂CaH₄(P₂O₇)₂, (NH₄)₂Ca₃(P₂O₇)₂.6H₂O, CaH₂P₂O₇ and α-Ca₂P₂O₇; and (ii) decreasing of temperature intervals of phase changes in comparison to untreated composite.     

Binding of SO2 by Synthetic Substituted Apatites

The reaction of SO₂ with synthetic apatites was studied by TG, XRD and IR analyses at 400-1000°C. Due to an interaction of apatite with SO₂, destruction of apatite and formation of CaSO₄ and diphosphate up to 750°C takes place. The further calcination leads to the formation of β-Ca₃(PO₄)₂ and a part of the SO₂ bound is lost again. The amount of SO₂ bound with apatite at calcination depends on the substitution ((F^- ↔ OH^-, PO₄ ^3- ↔ CO₃ ^2-, Ca²⁺ ↔ Mg²⁺) in its structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

Beiträge zum thermischen Verhalten und zur Kristallchemie von wasserfreien Phosphaten XXXII [1] Neue Orthophosphate des zweiwertigen Chroms — Mg3Cr3(PO4)4, Mg3, 75Cr2, 25(PO4)4, Ca3Cr3(PO4)4 und Ca2, 00Cr4, 00(PO4)4

Contributions on Crystal Chemistry and Thermal Behaviour of Anhydrous Phosphates. XXXII. New Orthophosphates of Divalent Chromium — Mg₃Cr₃(PO₄)₄, Mg_{3, 75}Cr_{2, 25}(PO₄)₄, Ca₃Cr₃(PO₄)₄ and Ca_{2, 00}Cr_{4, 00}(PO₄)₄ Solid state reactions via the gas phase led in the systems A₃(PO₄)₂ / Cr₃(PO₄)₂ (A = Mg, Ca) to the four new compounds Mg₃Cr₃(PO₄)₄ ( A ), Mg_3.75Cr_2.25(PO₄)₄ ( B ), Ca₃Cr₃(PO₄)₄ ( C ), and Ca_2.00Cr_4.00(PO₄)₄ ( D ). These were characterized by single crystal structure investigations [( A ): P2₁/n, Z = 1, a = 4.863(2) Å, b = 9.507(4) Å, c = 6.439(2) Å, β = 91.13(6)°, 1855 independend reflections, 63 parameters, R1 = 0.035, wR2 = 0.083; ( B ): P2₁/a, Z = 2, a = 6.427(2) Å, b = 9.363(2) Å, c = 10.051(3) Å, β = 106.16(3)°, 1687 indep. refl., 121 param., R1 = 0.032, wR2 = 0.085; ( C ): P‐1, Z = 2, a = 8.961(1) Å, b = 8.994(1) Å, c = 9.881(1) Å, α = 104.96(2)°, β = 106.03(2)°, γ = 110.19(2)°, 2908 indep. refl., 235 param., R1 = 0.036, wR2 = 0.111; ( D ): C2/c, Z = 4, a = 17.511(2) Å, b = 4.9933(6) Å, c = 16.825(2) Å, β = 117.95(1)°, 1506 indep. refl., 121 param., R1 = 0.034, wR2 = 0.098]. The crystal structures contain divalent chromium on various crystallographic sites, each showing a (4+n)‐coordination (n = 1, 2, 3). For the magnesium compounds and Ca_2.00Cr_4.00(PO₄)₄ a disorder of the divalent cations Mg²⁺/Cr²⁺ or Ca²⁺/Cr²⁺ is observed. Mg_3.75Cr_2.25(PO₄)₄ adopts a new structure type, while Mg₃Cr₃(PO₄)₄ is isotypic to Mg₃(PO₄)₂. Ca₃Cr₃(PO₄)₄ and Ca_2.00Cr_4.00(PO₄) ₄ are structurally very closely related and belong to the Ca₃Cu₃(PO₄)₄‐structure family. The orthophosphate Ca₉Cr(PO₄)₇, containing trivalent chromium, has been obtained besides C and D .     

Structure cristalline et spectres Raman polarises de Na1,5Sm8,5(SiO4)6FO

The silicated apatite Na_1.5Sm_8.5(SiO₄)₆FO crystallizes in the hexagonal system, with a=9.4761(6) Å, c=6.9484(4) Å cell parameters, P6₃/m space group, and Z=1. The samarium distribution over the 4f and 6h positions is not uniform. Due to their polarizability higher than the one of sodium, samarium ions mainly set on the 6h position, but their occupation of this position rate is limited by the valence required for fluorine. The Raman spectra, collected in various polarizations, are consistent with the proposed space group. An attribution of several external modes is given by comparison with the spectra of Ca₆Sm₂Na₂(PO₄)₆F₂, Ag₂Pb₈(PO₄)₆, Na₂Pb₈(PO₄)₆ and Ca₁₀(PO₄)₆F₂ (fluorapatite).     

On the existence of bivalent ions in the apatite channels: A new example—Phosphocalcium cyanamido-apatite

A new apatite, phosphocalcium cyanamido-apatite Ca₁₀(PO₄)₆ CN₂ □, is obtained by treatment under low pressure at high temperature (900–1000°C) of a mixture of the corresponding hydroxyapatite and calcium cyanamide. In this apatite, one CN^2?₂ ion associated with a vacancy replaces two hydroxyl ions in the channels. The formation of a cyanamide-containing apatite also occurs by treatment of an A-type carbonated apatite by ammonia at 600–900°C: in the latter case, the reaction seems more difficult and more limited than in the former. The cyanamido apatite is decomposed by heating in air, and it gives rise first to an A-type carbonated apatite, with release of both ammonia and nitrogen oxide and second to hydroxyapatite by hydrolysis of the A-type carbonated apatite.     

The revised phase diagram of the Ca3(PO4)2–YPO4 system. The temperature and concentration range of solid-solution phase fields

A revised version of the Ca₃(PO₄)₂–YPO₄ phase diagram has been proposed on the basis of results obtained by thermal analysis (DTA/DSC/TG) and X-ray diffraction methods. A limited solid solution with the structure of β-Ca₃(PO₄)₂ exists in the system. At 1,100 °C the maximal concentration of YPO₄ in the solid solution is ~15 mass%. The solid-solution phase field exists in the temperature range upto ~1,380 °C. Two high-temperature solid solutions with the structure of α′ and α-Ca₃(PO₄)₂ form in system as well, however only the α phase can be obtained by quenching from high temperatures. The Ca₃Y(PO₄)₃ compound with the structure of eulytite forms in the Ca₃(PO₄)₂–YPO₄ system at temperatures exceeding 1,255 °C and does not show any polymorphic transition.     

Application of the Peak Fitting Programme “Galactic” For FTIR-Analysis of OH-Ions in Natural and Synthetic Apatites

Abstract

Most of the studies on heavy metals binding ability of apatites have been carried out on hydroxyapatites (HA_P) [Ca_l0(PO₄)₆(OH)₂]. As the chemical characteristics of apatite depend substantially on the substitutions in its structure, the apatites with F substitution for OH and CO₃ ²for PO₄ ³ were studied.     

Cation Distribution Studies in Double Orthophosphates with Whitlockite Structure

Abstract

The structure of β-Ca₃ (PO₄)₂ is known to be similar to that of whitlockite (R3c, Z =21). The cations are distributed in five different positions, the position Ca(4) being only half occupied. The whitlockite network is stable while the filling of the Ca(4) position changes from 0 to 1. The presence of vacancies allows to provide heterovalent substitutions 3Ca²⁺ = 2M³⁺ + and Ca²⁺ + 0 = 2Me⁺ with limits of compositions Ca₉M (PO₄)₇ and Ca_loMe(PO₄)₇ respectively. The possible cation size can be changed from 0.55 Å (Fe³⁺) to 1.51 Å (K⁺). In order to check these suggestions we have synthesized Ca₉M(PO₄)₇ (M = rare earth element, Y, Bi, Fe, Al, In, Sc) compounds, The double phosphates were studied by luminescence, infrared spectroscopy and X-ray diffraction. All these compounds are isostructural to β-Ca₃(PO₄)₂. The cell parameters gradually decrease for M = La-Ho, Y and remain constant for M = Er-Lu. This divergence can be attributed to the change of the coordination number of the rare earth element. A considerable decrease of parameters is observed for the compounds of small-size trivalent elements, their IR spectra show more bands. By luminescence it was found that rare earth elements and Y, Bi occupy Ca(1), Ca(2), Ca(3) positions. The study of Ca_9.18 Fe_0.88 (PO₄)₇ structure shows that Fe³⁺ occupies octa-hedral Ca(5) site. The considerable decrease of lattice parameters and changes in IR spectra of compounds with M = Fe, Al, In, Sc result from the occupation of Ca(5) Site with trivalent cations and from redistribution of charges in the cation sublattice of the β-Ca₃(PO₄)₂ type structure.     

Thermal transformations in phosphorites

The thermal transformations in phosphorites during flash calcination were investigated by FT-IR spectroscopy, X-ray diffraction and chemical analyses. During flash calcination changes occur, both in the composition of the phosphorite and in the crystallochemistry of the fluor-carbonate-apatite (francolite). The former changes include: decomposition of a great part of the calcite in the rock and oxidation of organic matter. The latter changes include: partial removal of the structural carbonate; partial relocation of the remaining carbonate ions in the apatite structure; a new arrangement of hydroxyl groups and fluorine on the hexagonal axis; partial condensation of the orthophosphate groups and increase of crystallite sizes. Isomorphous substitution of PO ₄ ^–3 in apatite by SO ₄ ^–2 and SiO ₄ ^–4 may take place.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthdayThe financial support from Rotem-Amfert-Negev Phosphate Co. is gratefully acknowledged. We thank Dr. B. Pregerson of the Rotem-Amfert-Negev for supplying samples     

Quantum chemical and spectroscopic analysis of calcium hydroxyapatite and related materials

Amorphous calcium hydroxyapatite was examined by vibrational spectroscopy (Raman and infra-red (IR)) and quantum chemical simulation techniques. The structures and vibrational (IR, Raman and inelastic neutron scattering) spectra of PO₄³⁻ ion, Ca₃(PO₄)₂, [Ca₃(PO₄)₂]₃, Ca₅(PO₄)₃OH, CaHPO₄, [CaHPO₄]₂, Ca₃(PO₄)₂·H₂O, Ca₃(PO₄)₂·2H₂O and Ca₃(PO₄)₂·3H₂O clusters were quantum chemically simulated at ab initio and semiempirical levels of approximation. A complete coordinate analysis of the vibrational spectra was performed. The comparison of the theoretically simulated spectra with the experimental ones allows to identify correctly the phase composition of the amorphous calcium hydroxyapatite and related materials. The shape of the bands in the IR spectra of the hydroxoapatite can be used in order to characterize the structural properties of the material, e.g., the PO₄³⁻ ion status, the degree of hydrolysis of the material and the presence of hydrolysis products.     

Transformation of Calcium Dihydrogenphosphate in Mixtures with Apatite Concentrate Upon Heating

Abstract

The present work is related to an investigation of the chemistry of the phosphoric acid-thermal processing of apatite into a phosphate animal feed aupplement. Dried mixtures of H₃PO₄ with apatite concentrates of various mineral content and chemical composition as well as mixtures based on Ca(H₂PO₄2)₂ · H₂O, Ca₂P₂O₇ and Ca(PO₃)₂ were used. The investigation was carried out by chemical, thermal, chromatographic and X-ray diffraction methods.     

Reaction Mechanism in the Mixtures of Calcium Polyphosphate with Apatite and Accompanying Minerals on Heating

Abstract

On obtaining defluorinated feeding phosphates from Kovdor apatite the system of Ca₁₀(PO₄)₆(OH)_1,4F_0,6-CaCO₃-(Ca,Mg)CO₃-Mg₂SiO₄-Ca(H₂PO₄)₂·H₂O-Mg(H₂PO₄)₂·xH₂O with mole correlation (CaO+MgO)/P₂O₅V3 is subjected to thermal treatment. On heating up to 500°C calcium and magnesium hydrophosphates turn into polyphosphates M(PO₃)₂ which in accordance with the increase of the temperature react with other components of the system. To establish the mechanism and conditions for reactions, thermal interactions in the mixtures of Ca(PO₃₎₂ and Ca₂P₂O₇ with apatite, phorsterite, dolomite and calcite when (CaO+MgO)/P₂O₅=3 have been investigated. Methods of chemical, thermal, chromatographic, X-ray and IR-spectroscopy analysis were used.     

Dissolution De L'hydroxyapatite et Du Phosphate Tricalcique β Dans Les Solutions D'acide Nitrique

Using an isoperibol calorimeter for rapid reactions and a Calsol type microcalorimeter for slow processes, are applied to determine the enthalpies of solution of two synthetic phosphate products in nitric acid. Namely, β tricalcium phosphate Ca₃(PO₄)₂ and the calcium hydroxyapatite Ca₁₀ (PO₄)₆ (OH)₂ are measured by varying pH value of the solvent. Some dissolution mechanisms are proposed for various pH values. They are ensured by complementary reactions of solution of Ca(NO₃)₂, Ca(H₂ PO₄)₂ and H₃ PO₄ in the same solvents. An extrapolation of solution enthalpies to pH=7 leads to the enthalpy of solution of these products in the pure water. These values are Δ_sol H °=–138.3 kJ mol^–1 for Ca₃ (PO₄)₂ and –393.6 kJ mol^–1 for Ca₁₀ (PO₄)₆ (OH)₂ . This revised version was published online in August 2006 with corrections to the Cover Date.     

Solid solutions between β-Ca3(PO4)2 and sodium-containing whitlockite

Mixtures of CaHPO₄, CaCO₃, and Na₂CO₃ were heated at 870°C under steam or under dry CO₂ until phase composition and weight were constant. According to chemical analysis and X-ray diffractometry the stability field of the β-Ca₃(PO₄)₂ phase is limited by the molar P/Ca ratio of 0.664 ± 0.003 and 0.675 ± 0.010 irrespective of the partial water vapour pressure. A continuous series of solid solutions was found between β-Ca₃(PO₄)₂ and a new whitlockite with the composition Ca₁₀Na(PO₄)₇. The IR spectrum of these solid solutions shows that the point symmetry of the PO₄ groups and their environment increases with increasing sodium content. This is in agreement with data published about the structure of β-Ca₃(PO₄)₂ and whitlockite. The composition of these solid solutions suggests that Na⁺ ions can replace H⁺ ions in the whitlockite structure. Carbonate and pyrophosphate ions are not incorporated in these whitlockites.     

Phase equilibria in the ErPO4–K3PO4 system

The phase equilibria occurring in the ErPO₄–K₃PO₄ system were investigated by the thermal analysis, FTIR, and X-ray powder diffraction methods. On the basis of obtained results, the related phase diagram is proposed. This system includes one intermediate compound, K₃Er(PO₄)₂; the double phosphate melts incongruently at 1355 °C and occurs in two polymorphic forms; transformation β/α-K₃Er(PO₄)₂ proceeds at 420 °C. The eutectic occurs at the composition of 58.5 wt% K₃PO₄, 41.5 wt% ErPO₄ at 1317 °C.     

Preparation and exfoliation of layered titanium butyl phosphates

Titanium butyl phosphates (TiBP) synthesized by reacting Ti(SO₄)₂ with a mixture of mono-(C₄H₉PO₄H₂) and dibutyl phosphates ((C₄H₉)₂PO₄H) in aqueous ethanol solution at 25 °C were characterized by various conventional techniques. XRD pattern of TiBP possessed a peak at 2θ?=?5.5° and a broad hump at 2θ?=?15–30°. This fact indicated that the material was composed of a multilayer alternating bilayer of butyl groups of the phosphates and amorphous titanium phosphate phase. The TiBP was spherical particles with a size of ca. 100 nm and the chemical formula of this material was Ti((C₄H₉O)₂PO₂)_x(C₄H₉OPO₃)_y(OH)_z. The TiBP possessed a UV absorption property due to charge transfer of O^2? ? Ti⁴⁺. The layered structure of TiBP was exfoliated in ethanol at 25 °C up to TiBP concentration of 1.0?×?10⁵ ppm to form nanosheet. The nanosheet dispersing solution exhibited a UV absorption property and the property depends on nanosheet concentration.     

Comparative investigations of LiVPO4F/C and Li3V2(PO4)3/C synthesized in similar soft chemical route

Triclinic LiVPO₄F and monoclinic Li₃V₂(PO₄)₃ are synthesized through a soft chemical process with mechanical activation assist, followed by annealing. In this process, ascorbic acid is used as reducing agent as well as carbon source. The as-prepared samples are coated with amorphous carbon. XPS analysis results show the expected valency states of ions in LiVPO₄F and Li₃V₂(PO₄)₃. The electrochemical properties of the prepared LiVPO₄F/C and Li₃V₂(PO₄)₃/C cathodes are evaluated. The as-prepared LiVPO₄F/C cathode shows an initial discharge specific capacity of 140?±?3 mAh?g^?1 at 30 mA?g^?1 in the voltage range of 3.0~4.4 V, compared with that of 138?±?3 mAh?g^?1 possessed by Li₃V₂(PO₄)₃/C. Both samples exhibit good cycle performance at different current densities. The capacity delivered by LiVPO₄F remains 95.5 and 91.7 % of its initial discharge capacity after 50 cycles at 150 and 750 mA?g^?1, respectively, while 97.4 and 90.6 % for Li₃V₂(PO₄)₃/C. But the rate capability of LiVPO₄F/C is not so good compared with as-prepared Li₃V₂(PO₄)₃/C.     

Electrochemical performance of novel Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic nanocomposites as electrodes for energy storage devices

The novel Li₃V₂(PO₄)₃ glass-ceramic nanocomposites were synthesized and investigated as electrodes for energy storage devices. They were fabricated by heat treatment (HT) of 37.5Li₂O–25V₂O₅–37.5P₂O₅?mol% glass at 450 °C for different times in the air. XRD, SEM, and electrochemical methods were used to study the effect of HT time on the nanostructure and electrochemical performance for Li₃V₂(PO₄)₃ glass-ceramic nanocomposites electrodes. XRD patterns showed forming Li₃V₂(PO₄)₃ NASICON type with monoclinic structure. The crystalline sizes were found to be in the range of 32–56 nm. SEM morphologies exhibited non-uniform grains and changed with variation of HT time. The electrochemical performance of Li₃V₂(PO₄)₃ glass-ceramic nanocomposites was investigated by using galvanostatic charge/discharge methods, cyclic voltammetry, and electrochemical impedance spectroscopy in 1 M H₂SO₄ aqueous electrolyte. The glass-ceramic nanocomposites annealed for 4 h, which had a lower crystalline size, exhibited the best electrochemical performance with a specific capacity of 116.4 F g^?1 at 0.5 A g^?1. Small crystalline size supported the lithium ion mobility in the electrode by decreasing the ion diffusion pathway. Therefore, the Li₃V₂(PO₄)₃ glass-ceramic nanocomposites can be promising candidates for large-scale industrial applications in high-performance energy storage devices.