Hydrothermal conversion of Ti-containing minerals in system of Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–CaO–TiO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O

Titanium has a great effect on the digestion of bauxite in the Bayer process because it reacts readily at high temperatures in alkaline sodium aluminate solution. Under this consideration, the hydrothermal conversion of Ti-containing minerals in the system of Na₂O–Al₂O₃–SiO₂–CaO–TiO₂–H₂O with increased temperatures was studied based on the thermodynamic analysis and systematic experiments. The results show that anatase converts to Al₄Ti₂SiO₁₂ at low temperatures (60–120 °C), which is similar to anatase in crystal structure. As the temperature continues to rise, Al₄Ti₂SiO₁₂ decomposes gradually and converts to Ca₃TiSi₂(Al₂Si_0.5Ti_0.5)O₁₄ at 200 °C. When the temperature reaches 260 °C, CaTiO₃ forms as the most stable titanate species for its hexagonal closest packing with O^2? and Ca²⁺. The findings enhance the understanding of titanate scaling in the Bayer process and clarify the mechanism of how additive lime improves the digestion of diaspore.     

Stabilization of heavy metals in biochar pyrolyzed from phytoremediated giant reed (Arundo donax) biomass

The pyrolysis of phytoremediated giant reed (Arundo donax) biomass could cause secondary pollution of heavy metals. The stabilization of heavy metals in the pyrolysis process with external materials such as Al₂O₃, CaCO₃, FeCl₃ and NaOH, was studied. The results showed that 37% As and 97% Cd in biochar were stabilized when giant reed powder was pyrolyzed at 250 °C with 5% Al₂O₃ for 2 h. Furthermore, 59% Pb in biochar was stabilized at 400 °C with 5% CaCO₃ for 1 h. Under biochar produced in optimized pyrolysis conditions, Cd mainly existed in a residual fraction, while Pb and As mainly existed in oxidizable fraction in BCR analysis. In XRD analysis, As was only found in Ca₂As₂O₇; Cd in biochar mainly existed in Cd (AlCl₄)₂, CdPbO₃ or CdSO₃; and Pb mainly existed as Pb₃O₂SO₄.     

Thermodynamic and XRD analysis of reaction behaviors of gangue minerals in roasting mixture of scheelite and calcium carbonate for Ca3WO6 preparation

The conversion of unleachable scheelite (CaWO₄) to readily soluble Ca₃WO₆ in aqueous ammonium carbonate solution by roasting is crucial to the development of a green manufacturing technique for ammonium paratungstate. To better understand the influences of gangue minerals on the conversion of CaWO₄ to Ca₃WO₆, the reaction behaviors of gangue minerals in the scheelite concentrate such as quartz (SiO₂), apatite (Ca₅(PO₄)₃F), cassiterite (SnO₂), pyrite (FeS₂), molybdenite (MoS₂), and arsenopyrite (FeAsS) in the roasting process were investigated systematically in this work. Thermodynamic analyses and experimental results show that the gangue minerals except Ca₅(PO₄)₃F can react with CaCO₃ or Ca₃WO₆ to form corresponding calcium-containing compounds in roasting. There are Ca₃Fe₂WO₉, CaMoO₄, CaSO₄, and Ca₃(AsO₄)₂, etc. observed in the products when roasting in an oxidizing atmosphere, and Ca₂FeWO₆, CaS in a neutral or weakly reducing atmosphere, while the formations of Ca₂SiO₄, Ca₄Si₂O₇F₂, Ca₅(PO₄)₃F, CaSnO₃, and Ca₂SnO₄, etc. are independent of roasting atmosphere. The results suggest that these gangue minerals consume calcium and thus affect the conversion of CaWO₄ to Ca₃WO₆ in the roasting process, which can help determine the appropriate composition dosage for the complete conversion of CaWO₄ to Ca₃WO₆.     

Subsolidus Phase Relations of the CaO-REO<Subscript>x</Subscript><Emphasis Type="Bold">-</Emphasis>CuO Systems (RE = Eu,Tb, Dy,Ho, Er,Lu and Sc) at 900 °C in Air

The subsolidus phase relations of the CaO-REO_x-CuO systems (RE = Eu, Tb, Dy, Ho, Er, Lu and Sc) were investigated in air at 900 °C. The pseudo-ternary sections with RE = Tb, Dy, Ho, Er and Lu have a similar structure. They have in common with the RE = Eu system a solid solution of Ca_0.833?xRE_xCuO_2+y composition but the system with RE = Eu differs by the presence of an Eu₂CuO₄ phase instead of RE₂Cu₂O₅ for RE = Tb, Dy, Ho, Er and Lu. In contrast, the CaO-ScO_1.5-CuO section does not contain a Ca_0.833?xSc_xCuO_2+y solid solution and is dominated by the CaSc₂O₄ phase, which has no equivalent in the other systems at 900 °C in air.     

Luminescence properties of Ca10K(PO4)7:RE (RE = Ce, Tb, Dy, Tm and Sm) under vacuum ultraviolet excitation

A series of RE³⁺ (RE = Ce, Tb, Dy, Tm and Sm) activated Ca₁₀K(PO₄)₇ were synthesized by conventional state reaction and their photoluminescence properties under vacuum ultraviolet excitation were investigated. The PO₄³⁻ absorption lies within the range from 125 to 180 nm in all the excitation spectra of Ca₁₀K(PO₄)₇:RE³⁺. The first f-d transition of Ce³⁺ is observed at 316 nm, and the Ce³⁺ emission is located at about 350 nm. Both the first spin-allowed and spin-forbidden f-d transitions of Tb³⁺ are situated at 232 and 263 nm, respectively. The emission spectrum of Ca₁₀K(PO₄)₇:Tb³⁺ exhibits typical Tb³⁺ emissions with the predominant peak at 544 nm. The O²⁻-Dy³⁺ charge transition band was calculated and identified around 173 nm, the CIE chromaticity coordinates of Dy³⁺ were calculated to be 0.364 and 0.392. The Ca₁₀K(PO₄)₇:Tm³⁺ demonstrates the strongest excitation at about 182 nm assigned to O²⁻-Tm³⁺, and gives the predominant emission at 453 nm. The ⁴G_5/2-⁶H_7/2 transition of Sm³⁺ at 601 nm is the most intensive in the emission spectrum.     

Synthesis and characterization of Li<Subscript>1.3</Subscript>Al<Subscript>0.3</Subscript>Ti<Subscript>1.7</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>-coated LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> by wet chemical route

Li_1.3Al_0.3Ti_1.7(PO₄)₃-coated LiMn₂O₄ was prepared by wet chemical route. The phase, surface morphology, and electrochemical properties of the prepared powders were characterized by X-ray diffraction, scanning electron micrograph, and galvanostatic charge-discharge experiments. Li_1.3Al_0.3Ti_1.7(PO₄)₃-coated LiMn₂O₄ has similar X-ray diffraction patterns as LiMn₂O₄. The corner and border of Li_1.3Al_0.3Ti_1.7(PO₄)₃-coated LiMn₂O₄ particles are not as clear as the uncoated one. The two powders show similar values of lithium-ion diffusion coefficient. When cycled at room temperature and 55°C for 40 times at the charge-discharge rate of 0.2C, Li_1.3Al_0.3Ti_1.7(PO₄)₃-coated LiMn₂O₄ shows the capacity retentions of 98.2% and 93.9%, respectively, which are considerably higher than the values of 85.4% and 79.1% for the uncoated one. Both the capacity retention differences between Li_1.3Al_0.3Ti_1.7(PO₄)₃-coated LiMn₂O₄ and LiMn₂O₄ cycling at room temperature and 55°C become larger with the increase of charge-discharge rate. When the charge-discharge rate reaches 2C, the capacity retention of LATP-coated LiMn₂O₄ becomes 8.4% higher than the uncoated LiMn₂O₄ for room temperature cycling, and it becomes 11.1% higher than the latter when cycled at 55°C.     

Parallelogram-like microparticles of calcium dihydrogen phosphate monohydrate (Ca(H2PO4)2·H2O) obtained by a rapid precipitation route in aqueous and acetone media

Calcium dihydrogenphosphate monohydrate (Ca(H₂PO₄)₂·H₂O) was prepared by a rapid and simple precipitation method using CaCO₃ and H₃PO₄ in aqueous and acetone media at ambient temperature. The thermal transformation of the synthesized Ca(H₂PO₄)₂·H₂O at 500 °C was obtained to be CaP₂O₆ occurred through the dehydration and the phosphate condensation reactions, as revealed by thermoanalytical techniques (TG/DTG/DTA). The synthesized Ca(H₂PO₄)₂·H₂O and its decomposition product CaP₂O₆ were characterized by X-ray powder diffraction (XRD), Fourier transfer infrared (FTIR) spectroscopy and scanning electron microscope (SEM). Thermal behavior and the morphology of the synthesized Ca(H₂PO₄)₂·H₂O in aqueous and acetone media are compared with those of other works. The SEM micrograph of Ca(H₂PO₄)₂·H₂O show parallelogram-like microparticles containing small and large grain sizes. The aqueous and acetone media are proposed to play an important role in the synthetic process of calcium phosphates in exhibiting different physical properties, which are important for specific applications.     

Interfacial tension and contact angle variations of SUS304 melt in contact with solid oxides and CaO-SiO2-Al2O3(CaF2) slags at 1470°C

Study on the interfacial properties of SUS304 melt in contact with pedestal oxides and also liquid slags of varying chemistry was carried out by using a combination of the sessile drop method and a X-ray fluoroscopic technique at 1470°C. Interfacial tension and contact angle were obtained directly from a numerical solution of the Young-laplace equation. Surface tension of SUS304 was found to be 1467 mN.m in Ar-atmosphere which was considerably lower than that of pure iron. This may be due to the existence of surface active elements such as (Cr, Ni and Mn etc. in SUS304. Interfacial tensions of SUS304 in contact with CaO-Sio₂-Al₂O₃(CaF₂) slags were in the range of 925 to 1 148 mN/m. The contact angle between SUS 304 and various pedestal was about 120° regardless of pedestal oxides. A1₂O₃. TiO₂ and SiO₂. Contact angles between SUS304 and the pedestal alumina coexisting with liquid CaO-SiO₂-Al₂O₃CaF₃) were in the range of 125° to 142°.     

High temperature dephosphorization behavior of monazite concentrate with charred coal

Dephosphorization behavior of monazite concentrate with charred coal at high temperature was investigated.It is found that the roast temperature is the main factor for the dephosphorization of the monazite.The high dephosphorization efficiency can be reached at the temperatures ranging from 1 200 to 1 400°C.When the monazite pellets,made by pressing mixture of the monazite,charred coal and water into mould,were roasted at 1 400°C for 2 h,98%of phosphorus was removed from the monazite pellets.The roast time has little effect on the dephosphorization efficiency.Meanwhile,the particle size of the charred coal also has great influence on the dephosphorization efficiency of the monazite,and it is better to control particle size around 150μm,while Fe and Fe2O3 have neglectable effect on the dephosphorization of the monazite.     

CMAS corrosion resistance characteristics of RE50TaxZr50-xO175+0.5x thermal barrier oxides in RE2Zr2O7-RETaO4 systems

The corrosion resistance characteristics of RE-rich RE₅₀Ta_xZr_50-xO_175+0.5x oxides in RE₂Zr₂O₇-RETaO₄ systems to calcium-magnesium-alumino-silicate (CMAS) at 1300 °C, and the influence of RE³⁺ and Ta⁵⁺ on chemical reactions and reactive crystallization of CMAS melts were investigated. The results show that following the thermochemical reactions, apatite, pyrochlore, reprecipitated fluorite and residual Yb(Y)TaO₄ phases were the predominant reaction products. Formation abilities of apatite and pyrochlore were found to be proportional to the ionic radius of RE³⁺. The increase of Ta⁵⁺ amount can decrease the number of available RE³⁺ to form apatite. Moreover, the resistance characteristic to CMAS corrosion in RE₅₀Ta_xZr_50-xO_175+0.5x systems was decided by the combined action of apatite and pyrochlore phases. The cohesive mixture of apatite and pyrochlore phases can generate a dense layer near the reaction front, which had a positive effect on suppressing CMAS infiltration. The ability of the fluorite + RETaO₄ two-phase field was determined to be sufficient to mitigate CMAS corrosion.     

Phase Relations in the System CaO-Fe2O3-Y2O3 at 1273?K and Compatibility Between Y1?xCaxFeO3?0.5x and Stabilized Zirconia

Phase relations in the system CaO-Fe₂O₃-Y₂O₃ in air (( P_\textO2 P_{{{\text{O}}_{2} }} /P°) = 0.21) were explored by equilibrating samples representing eleven compositions in the ternary at 1273 K, followed by quenching to room temperature and phase identification using XRD. Limited mutual solubility was observed between YFeO₃ and Ca₂Fe₂O₅. No quaternary oxide was identified. An isothermal section of the phase diagram at 1273 K was constructed from the results. Five three-phase regions and four extended two-phase regions were observed. The extended two-phase regions arise from the limited solid solutions based on the ternary oxides YFeO₃ and Ca₂Fe₂O₅. Activities of CaO, Fe₂O₃ and Y₂O₃ in the three-phase fields were computed using recently measured thermodynamic data on the ternary oxides. The experimental phase diagram is consistent with thermodynamic data. The computed activities of CaO indicate that compositions of CaO-doped YFeO₃ exhibiting good electrical conductivity are not compatible with zirconia-based electrolytes; CaO will react with ZrO₂ to form CaZrO₃.     

Preparation of Ti-rich material from titanium slag by activation roasting followed by acid leaching

A method of activation roasting followed by acid leaching using titanium slag was introduced to prepare Ti-rich material. The effects of H₃PO₄ dosage, roasting temperature, and roasting time on TiO₂ grade were investigated. A Ti-rich material containing 88.54% TiO₂, 0.42% (CaO+MgO) was obtained when finely ground titanium slag was roasted with 7.5% H₃PO₄ at 1000 °C for 2 h, followed by a two-stage leaching in boiling dilute sulfuric acid for 2 h. The XRD patterns show that the product is titanium dioxide with a rutile structure. Mechanism studies show that structures of anosovite solid solution and silicate minerals are destroyed in the roasting process. As a result, titanium components in titanium slag are transformed into TiO₂ (rutile) while impurities are transformed into acid-soluble phosphate and quartz.     

白云鄂博混合型稀土精矿在惰性气氛下的热分解行为（英文）

为了开发和应用白云鄂博混合型稀土精矿的先进冶炼技术，采用Kissinger公式、TGA-DSC和XRD等分析方法，研究在氮气氛下白云鄂博混合型稀土精矿的热分解行为，包括热分解动力学、物相变化规律、铈氧化效率以及物相变化对稀土浸出率的影响。结果表明：在500～550℃焙烧时，焙烧质量损失率约10%、热分解活化能(E_a)为148 k J/mol。550℃焙烧2 h，白云鄂博混合型稀土精矿中氟碳铈矿完全分解，并转化为稀土氧化物和氟氧化物，铈氧化率最大值为0.58%。600℃焙烧2 h，稀土最大浸出率达49.1%。     

介孔Li3V2（PO4）3正极材料的研磨溶胶凝胶法合成和电化学性能（英文）

以V2O5·nH2O、LiOH·H2O、NH4H2PO4和蔗糖为原料,采用研磨溶胶凝胶技术制备了无定形Li3V2(PO4)3前驱体,再经过焙烧获得具有单斜结构的介孔Li3V2(PO4)3正极材料,并用XRD、SEM、TEM、比表面积和电化学性能测试来表征材料的性能。研究表明,在700°C下焙烧的样品具有良好的介孔结构、最大的比表面积(188cm2/g)和最小的孔径(9.3nm)。在0.2C倍率下,该介孔样品的首次放电容量达155.9mA·h/g,经过50次循环后其容量仍然可达154mA·h/g,表现出非常稳定的放电性能。     

On the mechanism of formation of zinc pack coatings

The mechanism of the formation of zinc (Zn) pack coatings is studied with scanning electron microscopy (SEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). DSC showed that the coatings formation takes place in three steps. The initial step (at 193.9 °C) is endothermic and involves the transformation of α-NH₄Cl to β-NH₄Cl and the NH₄Cl decomposition to NH₃ and HCl. During the second step (at 248.6 °C), which is exothermic, Zn²⁺ salts are formed and especially ZnCl₂. Finally at 264.1 °C Zn is deposited by an endothermic reaction on the ferrous substrate through the decomposition of ZnCl₂. The as-cast Zn diffuses into the iron lattice forming the gamma (Γ-Fe₁₁Zn₄₀) and delta (δ-FeZn₁₀) phases. Al₂O₃ is not involved in the above-mentioned mechanism and acts only as filler.     

Thermodynamic and experimental studies on removal of calcium and sulfate ions from recycling water of complex sulfide flotation operations

A chemical method for removing calcium sulfate saturated solutions (0.016 mol/L CaSO₄) using barium chloride (BaCl₂·2H₂O) and sodium phosphate (Na₃PO₄) was experimentally studied. The main interest is to remove these ions from the solution through the precipitation of two solid species: sulfate (SO₄²⁻) as barite (BaSO₄), and calcium (Ca²⁺) as hydroxyapatite (Ca₅(PO₄)₃OH). Additionally, a solid/liquid separation method (i.e., flotation) was explored, using oleic acid and dodecylamine as collectors. The results show that, the chemical treatment of saturated solutions at 60 °C, pH 11.5 and using 3.9 g/L BaCl₂·2H₂O and 1.6 g/L Na₃PO₄, promotes the precipitation of barium sulfate and calcium-deficient hydroxyapatite (Ca_10–x(HPO₄)_x(PO₄)_6–x(OH)_2–x), with residual concentrations of calcium and sulfate below 0.10 and 5 mg/L, respectively. The residual calcium concentration increases to 28 mg/L when using the same amount of reactants, at temperature and pH values below those quoted. The highest flotation recovery of hydroxyapatite with oleic acid at pH 9.5 was about 80%, while that of barite floated with dodecylamine at pH 6.5 was about 90%.     

Activities of Fe,FeO, Fe<Subscript>2</Subscript>0<Subscript>3</Subscript>, and CaO in Simple Slags

The data previously reported for the quantity j = Fe⁺⁺⁺/(Fe⁺⁺+Fe⁺⁺⁺) as a function of oxygen pressure at 1550°C have been used to compute the activities of Fe, FeO, Fe₂O₃, and CaO in slags of the ternary system. Activities of the first three have been obtained also for two quasi-ternaries involving fixed CaO:SiO₂ ratios.     

Effect of Ca-doping on the structural and electrical properties of CuY1−xCaxO2 (0 ≤x ≤0.10) ceramics

Delafossites CuY_1−xCa_xO₂ (0 ≤x ≤0.10) ceramics have been prepared by solid state reaction using Cu₂O, Y₂O₃ and CaCO₃. Liquid phase sintering, which obviously accelerates the reaction speed of Cu₂O-Y₂O₃-CaCO₃ system and promotes the formation of CuYO₂ phase is evidenced for the Ca-doped samples. During the sintering process, CuO can react with CaO to form two intermediate compounds, CaCu₂O₃ and Ca₂CuO₃, which decompose into CaO and liquid phase during 1273-1323 K. In the dopant range of 0 ≤x ≤0.10, both electrical conductivity and density of the samples are increased by Ca-doping. The room temperature conductivity of CuY_0.94Ca_0.06O₂ is more than four orders of magnitude higher than that of CuYO₂.     

Vanadium recovery from stone coal through roasting and flotation

A new process for vanadium recovery from stone coal by roasting–flotation was investigated based on the mineralogy. The process comprised four key steps: decarburization, preferential grinding, desliming and flotation. In the decarburization stage, roasting at 550 °C effectively avoided the negative effect of the carbonaceous materials in raw ore and generation of free CaO from calcite decomposition during roasting. Through preferential grinding, the high acid-consuming minerals were enriched in the middle fractions, while mica was enriched in the fine and coarse fractions. Through flotation, the final concentrate can be obtained with V₂O₅ grade of 1.07% and recovery of 83.30%. Moreover, the vanadium leaching rate of the final concentrate increased 13.53% compared to that of the feed. The results reveal that the decarburization by roasting at 550 °C is feasible and has little negative impact on mica flotation, and vanadium recovery from stone coal is conducive to reducing handling quantity, acid consumption and production cost.     

Crystal chemistry of organic minerals – salts of organic acids: the synthetic approach

The term ‘organic minerals’ means naturally occurring crystalline organic compounds including metal salts of formic, acetic, citric, mellitic, methanesulfonic and oxalic acids. As for the rest of the (inorganic) minerals, the primary tool to disclose their crystal and molecular structure and therefore to understand their mutual relationship with each other and with synthetic analogues and also their physicochemical properties is X-ray diffraction crystallography ever since the dawn of this methodology in 1913. The structure of several synthetic organic minerals was solved well before the discovery of their natural counterpart. On the other hand, complete crystal structure determination of early discovered organic minerals had to await the advent of combined synthetic and advanced X-ray diffraction methods to fully unveil their crystal structures. We review here the crystal chemistry of organic minerals and show the importance of structural studies on their synthetic analogues. This will be highlighted by case studies on the recently reported synthetic novgorodovaite, Ca₂(C₂O₄)Cl₂·2H₂O, and its heptahydrate analogue, Ca₂(C₂O₄)Cl₂·7H₂O, and the isotypic to each other stepanovite, NaMg[Fe(C₂O₄)₃]·9H₂O, and zhemchuzhnikovite, NaMg[Al_xFe_1?x(C₂O₄)₃]·9H₂O.