Precipitation Of CaO Research Articles

Mechanism of ultrasonic-enhanced leaching for separating organic impurities from the surface of bauxite and H2O2 oxidation-CaO precipitation for purifying the leaching solution

The existence of organic impurities in bauxite significantly hampers the regular production of alumina. This study proposes a low-temperature ultrasonic-enhanced alkali leaching to directly separate organic impurities from bauxite, and purify the leaching solution through H2O2 oxidation and CaO precipitation. Under the optimal conditions of 550 W ultrasonic power, 80 °C, 60 min, and 200 g/L NaOH concentration, the leaching rate of organic carbon in bauxite is 91.02 %, which is 19.01 % higher than conventional alkali leaching, and the organic carbon content in the bauxite decreased from 0.59 % to 0.06 % after leaching. Kinetic studies indicate that the limiting factors of the leaching rate vary under different leaching temperatures and leaching times. Characterization of bauxite before and after leaching using various detection techniques demonstrates the effective separation of organic impurities while basically no loss of alumina and increasing the alumina to silica ratio to 34.13. Subsequently, H2O2 and CaO are introduced to the leaching solution with 20 % and 800 mL/g, respectively. The oxidation process under 550 W ultrasonic power at 90 °C for 60 min achieves an 71.35 % removal rate of organic carbon. GC-MS analysis confirms the successful removal of the main organic substances in the leaching solution, while XRD analysis of the oxidation residue indicates that organic substances are ultimately removed as CaC2O4·H2O and CaCO3. Additionally, a proposed free radical reaction mechanism of H2O2 oxidizing organic substances is discussed. In conclusion, this study providing valuable insights for the removal of organic pollutants in the alumina production process.

H2O2 oxidation – CaO precipitation pretreatment combining forward osmosis for electroless nickel spent tank liquid (ENSTL) reduction

ABSTRACT The electroless nickel spent tank liquid (ENSTL), as a typical hazardous waste, contains a variety of refractory organic substances as well as heavy metals and inorganic salts. Generally, ENSTL is delegated for disposing by qualified hazardous waste disposal departments in China. However, the temporary storage, transportation, and higher entrusted disposal expenses increase the burden on enterprises producing the hazardous ENSTL. This paper explored an oxidation/precipitation pretreatment and forward osmosis (FO) combined process for ENSTL reduction. 400 mmol/L Hydrogen peroxide and 5.0 wt% calcium oxide were selected as the optimal pretreatment in order to minimize the osmotic pressure of ENSTL, by which the conductivity was significantly reduced from 50.8 mS/cm to 26.8 mS/cm. As a result, the concentrating factor (N) could be dramatically increased from 2.45 by the direct FO to 8.71 by the combined system. Accordingly, the average water flux during the 24 h concentrating cycle increased from 2.47 L/(m2·h) to 4.56 L/(m2·h). TOC rejection rate decreased from 90.23% to 84.39% due to the transformation of organic matter forms by the chemical oxidation during the pretreatment. Meanwhile, TP, Ni and NH4 + rejection rates decreased to a certain extent, which may related to the mitigation of membrane fouling by the pretreatment.

The precipitation process for a rare earth leach solution with calcium oxide in the presence of ascorbate and calcination to oxide of high purity

Sulfate ions coprecipitate with rare earth metal ions to form alkaline rare earth sulfate (RE2(OH)4SO4) in the CaO precipitation process, leading to excessive content of sulfate in the mixed rare earth oxide. Due to the difference of coordination ability between ascorbate, sulfate, hydroxyl and rare earth metal ions, ascorbate is introduced into the pregnant leach solution (PLS) during the CaO precipitation process. It realizes the coprecipitation between ascorbate (C6H7O6−) and rare earth metal ions, reducing the formation of RE2(OH)4SO4 and improving the purity of mixed rare earth oxide. In this paper, the standard reaction Gibbs free energy changes of the possible reactions in the precipitation process were calculated using the group contribution method, to draw the species distribution equilibrium diagram with Newton's iteration method. When ascorbate exists, rare earth metal ions in the PLS tend to form the alkaline rare earth ascorbate (RE2(OH)4(C6H7O6)2) instead of RE2(OH)4SO4. Furthermore, the effect of the reaction conditions on the precipitation process were studied. When the molar ratio of rare earth metal ions to ascorbate was 1.17, the purity of the mixed rare earth oxide was 96.2 wt% and the sulfate content was 2.2 wt%. Finally, based on the results of the material balance calculation, FTIR, XRD and TG-DSC tests, it was further confirmed that ascorbate participated in the form of RE2(OH)4(C6H7O6)2, and effectively suppressed the generation of RE2(OH)4SO4. Consequently, the results facilitate the green and efficient extraction of rare earths from the ion-adsorption type ore.

Selective precipitation and non-isothermal crystallization kinetics of britholite from low grade REE-bearing slag

In order to improve the recovery rate of rare earth, the effect of P2O5 and cooling rate on the selective precipitation of CaO–SiO2–TiO2–P2O5–Nb2O5–CeO2–CaF2 slag system was explored using X-ray powder diffraction, a scanning electron microscope, an electron probe micro-analyzer and a confocal laser scanning microscope. The apatite (Ca2.02Ce7.98Si6.00O26.00) is tiny and difficult to be separated from the slag without P2O5. When the addition of P2O5 is 6 wt%–10 wt%, the cerium and phosphorus are found to be enriched in britholite (Ca5–xCex[(SiO4)x(PO4)3–x]F) phase while x is negatively correlated with P2O5 content in the slag. The influence of P2O5 and cooling rate on the non-isothermal crystallization kinetics was also investigated. For the cooling rate between 5 and 40 °C/min, continuous cooling transformation diagram of britholite was constructed when the P2O5 content is between 6 wt%–10 wt%. The modified Avrami model was applied to determine the crystallization mode of slag with 10 wt% P2O5. It is shown that the crystallization mode is diffusion-controlled with constant nucleation rate and one-dimensional growth. In consideration of quantity and volume of crystals, the reasonable cooling rate is between 10 and 30 °C/min.

Effect of high pressure and high temperature on the Na2O · 2CaO · 3SiO2 glass-ceramic’s structural properties

In this study, the Soda-lime-silicate system, with the Na2O·2CaO·3SiO2 (N1C2S3) composition, was used to study the effect of high pressure on structural properties of this glass-ceramic. Samples were produced and submitted to a single stage crystallization heat treatment at 720 °C for 30 min simultaneously in atmospheric pressure, 2.5 GPa, 4.0 GPa or 7.7 GPa. All characterizations were performed ex-situ. The major crystalline phase obtained is the Combeite, regardless of the pressure used, with indications of a β−CaSiO3 or Cristobalite-II phase transition happening due to the high pressure. Raman and Infrared spectroscopy showed that the phase transition could be a CaO precipitation on the material, due to the breaking of Si–O bonds and presence of Ca–O vibrational modes present on the high pressure samples. All results point to the Combeite crystalline phase being highly stable under pressures up to 7.7 GPa.

Effect of rare earth oxide on the crystallization behavior of CaO-Al2O3-based mold flux for rare earth heat-resistant steel continuous casting

New CaO-Al2O3-based mold flux for rare earth steel continuous casting was devised to restrain the slag-steel interface reaction. The effect of Ce2O3 on the crystallization behavior were investigated. The continuous cooling transformation tests show that the addition of Ce2O3 not only reduces the critical cooling rate of the mold flux but also reduces the initial crystallization temperature. Besides, the distribution of the initial crystallization temperature became more stable. The temperature time transformation tests show that the crystallization incubation time is slightly increased, the addition of Ce2O3 inhibit the isothermal crystallization process to a certain extent. The crystalline phases changed from LiAlO2+CaO to LiAlO2+CaCeAlO4. The precipitation of CaO was restrained by adding Ce2O3. With the combination of Ca2+, Ce3+, and [AlO69−]-octahedron units, CaCeAlO4 formed and precipitated in the crystallization process. Besides inhibiting the crystallization of CaO-Al2O3-based mold flux, adding rare earth oxide also can reduce the viscosity and the breaking temperature.

Effects of CeO2 on Viscosity, Structure, and Crystallization of Mold Fluxes for Casting Rare Earths Alloyed Steels

The CaO-Al2O3-based mold fluxes are proposed for the Ce-bearing heavy rail steel continuous casting because of the low reactivity. Effects of CeO2 on the melting temperature, the viscous property, and the crystallization behavior of the CaO-Al2O3-Li2O-B2O3 mold fluxes were studied using hemisphere melting point method, rotating cylinder method, and X-ray diffraction (XRD) in the present work. The microstructure of the mold fluxes was analyzed by Fourier-transform infrared spectroscopy (FTIR). The results revealed that the addition of CeO2 would increase the melting temperature, but decrease the viscosity at each temperature due to its influence on increasing the depolymerization of the mold fluxes at high temperature. The precipitation of CaO was restrained and CaCeAlO4 generated with increasing CeO2 content since the crystal phases were affected by the microstructure of the melts. The change of the crystalline phases in mold fluxes influences the break temperature and the viscosity of the mold fluxes below the break temperature. These results obtained can provide guidelines for designing new mold fluxes for casting rare earth alloy heavy rail steels.

Purification of Tea Saponins and Evaluation of its Effect on Alcohol Dehydrogenase Activity.

Tea saponins, extracted from a Camellia oleifera cake, were found to have a potent effect on de-alcoholic activity. To obtain highly pure tea saponins, which can better maintain the activity of alcohol dehydrogenase (ADH), this paper presents an extraction method for tea saponins using deionized water as the extraction agent and a two-stage precipitation method, including ethanol precipitation and CaO precipitation. The optimum conditions for ethanol precipitation were 95% alcohol, a duration of 1.5h and a solid/liquid ratio of 1:4; while the optimum conditions for CaO precipitation were a duration of 2h and an NH4HCO3/CaO ratio of 2:1. Under the optimum conditions, the content of saponins was 87.58%. The results showed that the greater the amount of tea saponins and the higher its purity, the more significant its activating effect on ADH. When the purity of tea saponins was above 75%, it activated ADH. It indicated that the de-alcoholic mechanism of tea saponins is associated with the activity of ADH. Furthermore, the study characterized the structure of tea saponins by UV absorption and Fourier Transform Infrared (FTIR) spectrometry and LC-MS.

Viscous properties of new mould flux based on aluminate system with CeO2 for continuous casting of RE alloyed heat resistant steel

AbstractThe conventional mould fluxes can not be applied to the continuous casting of RE alloyed heat resistant steel, because severe slag-metal interface reactions occur generally in the mold. To restrain the interface reaction and improve conditions for continuous casting, a new mould flux based on aluminate system was devised. The viscous properties were investigated. Scanning electron microscopy and X-ray diffraction were applied to detect and characterize the crystalline phases in the continuous cooling process. The results showed that appropriate addition of CeO2 could avoid the precipitation of CaO and decrease the viscosity of the mould flux. Increasing the mass ratio of CaO/Al2O3, especially to a value exceeding 1, could worsen the stability of the mould flux. With a content of less than 14 wt.%, Li2O could reduce the viscosity and breaking temperature, but its effect could be weakened for the promoted precipitation of LiAlO2. To obtain a mould flux with stable viscous properties, such as viscosity and breaking temperature, appropriate contents of CeO2 and Li2O should be controlled to around 10 wt.% and 14 wt.%, while the mass ratio of CaO/Al2O3 should not be more than 1.

Study of a New Mold Flux for Heat‐Resistant Steel Containing Cerium Continuous Casting

New mold fluxes with CaO–Al2O3–Li2O–CeO2 system are proposed for heat‐resistant steel continuous casting. The fundamental properties are investigated systematically. It is found that the appropriate content of CeO2 is determined to be ≈10 wt%, the melting temperature did not change much with increasing CeO2 content, which indicates that the mold fluxes could show steady smelting properties after continuously absorbing inclusions containing cerium in the continuous casting process. After adding CeO2, the precipitation of CaO in the crystallization process is restrained, and the crystalline phases are shifted from CaO/LiAlO2 to CaCeAlO4/LiAlO2. It is further evidenced that the precipitation of CaCeAlO4 and LiAlO2 can be restrained by CeO2. CeO2 shows significantly positive influence in decreasing the viscosity. Above the breaking temperature, the decrease of viscosity is attributed by the cutting off the chain structure of the molten slag from CeO2. Below the breaking temperature, it is caused by the effect of CeO2 on restraining the crystallization process. The optimal content of Li2O is 14 wt%, with a content of less than 14 wt%, Li2O can reduce the melting temperature and viscosities obviously, but the fluxing action of Li2O becomes ineffective when the content of Li2O exceeds 14 wt%. The results have great theoretical significance for developing mold fluxes for heat‐resistant steel.

Low-temperature crystallization and high-temperature instability of hydroxyapatite thin films deposited on Ru, Ti, and Pt metal substrates

We investigated the crystallinity, orientation, and stability of hydroxyapatite (HAp) thin films on structural materials including SiO2 and metals (Ru, Ti, and Pt). The HAp films were deposited by electron cyclotron resonance (ECR) plasma sputtering with an Xe sputtering gas under simultaneous flow of H2O vapor. The HAp films as-crystallized during deposition and solid-phase crystallized by post annealing were analyzed with X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman scattering. The lowest solid-phase crystallization temperatures were 350°C on Ru, 300°C on Ti, and 300°C on Pt. These crystallization temperatures are much lower than those on silicon and SiO2 substrates (550°C). For HAp films as-crystallized at temperatures above 400°C, the elements out diffused and reacted with substrates. Precipitation of CaO was observed for HAp films deposited on SiO2 and Ru substrates. Diffusion of PO43− into SiO2 and Ru-catalyzed decomposition of HAp crystals are suggested for the mechanism. When deposited on Pt substrates, CaPt2O4 alloy byproducts were created for solid-phase crystallized films and CaPt2 alloy byproducts were created for as-crystallized films, indicating reaction of Ca atoms with Pt substrates.

加熱したCa/P モル比1.70 の球状ハイドロキシアパタイトからのCaO の析出

加熱したCa/P モル比1.70 の球状ハイドロキシアパタイトからのCaO の析出

The Study of Magnesium Substitution Effect on Physicochemical Properties of Hydroxyapatite

In the present study, pure and Mg-substituted hydroxyapatite powders made up of needle-like and plate-like particles, respectively, have been synthesized by wet chemical precipitation of CaO, MgO and H3PO4. The influence of different amounts of MgO addition into synthesis media on properties of as-synthesized and sintered powders has been evaluated. Through the phase and chemical composition analysis it has been determined that the prepared powders contain various amounts of Mg (in the range between 0.21–4.72 wt%). The substitution of Mg promoted the decomposition of hydroxyapatite to β-tricalcium phosphate.

Glyphosate Wastewater Treatment by Combined Precipitation and Advanced Oxidation Processes

Phosphorus is one of the main pollutants in glyphosate wastewater. In order to remove the phosphorus in the effluent, two units including CaO precipitation and advanced oxidation processes (AOPs) were used to degrade inorganic phosphate and organic phosphorus in the wastewater. It is found that in the precipitation process the removal rate of TP is 79% when 1g CaO is added to 100ml glyphosate wastewater, while the removal rate of TP is almost 99% when advanced oxidation processes are implemented after the second disposal unit.

Usefulness of gel-casting method in the fabrication of nonstoichiometric CaZrO 3-based electrolytes for high temperature application

Hydrogels obtained from lower toxicity monomers of N-(hydroxymethyl)acrylamide and N, N′-methylenebisacrylamide were applied to form nonstoichiometric CaZrO 3-based electrolytes. A coprecipitation-calcination method with ((NH 4) 2C 2O 4) in concentrated NH 3 aqueous solution was used to synthesise CaZrO 3 involving 51 mol.% CaO (CZ-51) powder. The gas-tight CaZrO 3-based rods were prepared by the gel-casting method with 45 vol.% suspension and then sintered at 1500 °C–2 h. It was found that in low oxygen partial pressure, the nonstoichiometric CaZrO 3 obtained by gel-casting method were pure oxide ion conductors. These samples exhibited comparable electrical conductivity values to isostatically compressed pellets starting from the same powder. The results of experiments on thermochemical stability of CZ-51 gel-cast shapes at high temperatures in air or gas mixtures involving 2–50 vol.% H 2, as well as the corrosion resistance in exhaust gases from a self-ignition engine were also presented and discussed. The thermal resistance of CaZrO 3 obtained rods against molten nickel or iron was also examined. Based upon these investigations, it is evident that only in hydrogen-rich gas atmospheres can the stability of CaZrO 3 shapes be limited due to the presence of CaO precipitation as a second phase. The nonstoichiometric CaZrO 3 (CZ-51) gel-cast materials were also tested in solid galvanic cells, designed to study thermodynamic properties of oxide materials, important for SOFC and energy technology devices. In this way, the Gibbs energy of NiM 2O 4, M = Cr, Fe, at 650–1000 °C was determined. The CaZrO 3 involving 51 mol.% CaO gel-cast sintered shapes seems to be promising solid electrolytes for electrochemical oxygen probes in control of metal processing and thermodynamic studies of materials important for the development of the energy industry.

Electrochemically Driven Three‐Phase Interlines into Insulator Compounds: Electroreduction of Solid SiO2 in Molten CaCl2

The electrochemical reduction of solid SiO2 (quartz) to Si is studied in molten CaCl2 at 1173 K. Experimental observations are compared and agree well with a novel penetration model in relation with electrochemistry at the dynamic conductor|insulator|electrolyte three-phase interlines. The findings show that the reduction of a cylindrical quartz pellet at certain potentials is mainly determined by the diffusion of the O(2-) ions and also the ohmic polarisation in the reduction-generated porous silicon layer. The reduction rate increases with the overpotential to a maximum after which the process is retarded, most likely due to precipitation of CaO in the reaction region (cathodic passivation). Data are reported on the reduction rate, current efficiency and energy consumption during the electroreduction of quartz under potentiostatic conditions. These theoretical and experimental findings form the basis for an in-depth discussion on the optimisation of the electroreduction method for the production of silicon.

X-Ray Diffractometry and X-Ray Photoelectron Spectroscopy Investigations of Nanocrytalline Hydroxyapatite Synthesized by a Hydroxide Gel Technique

Nanocrystalline hydroxyapatite (HA), Ca10(PO4)6(OH)2, has been synthesized by a precipitate-conversion technique using hydroxide gel. Hydroxyapatite crystallizes in a hexagonal structure (space group; P63/m) having lattice parameters; a=9.407 Å and c=6.883 Å, and around 37 nm in size for the 800°C-annealed sample. Substantial crystalline characteristics are observed for the material heat-treated at 80°C. With the increase of air-annealing temperature, from 80°C to 800°C, lattice expansion along all crystallographic axes occurs indicating a structural change in the HA lattice. These results have been attributed to (1) the formation of a relative Ca2+ deficiency in HA that incorporates various chemical species in the anionic sites compared to their lower temperature air-annealed counterparts, and (2) the precipitation of CaO with increasing air-annealing temperature. The X-ray photoelectron spectroscopy studies indicate a distorted anionic structure and two electronic states for the O1 s, corroborating the observed X-ray diffraction results.

Studies of the relative acidities of some chloride melts

A potentiometric titration method was used to determine the solubility products (p P=−log P) of some oxides at 700°C in molten chloride mixtures of the following compositions, CaC1 2–KCl (0.235:0.765); SrCl 2–KCl–NaCl (0.22:0.42:0.36); BaCl 2–KCl–NaCl (0.43:0.29:0.28); and BaCl 2–KCl (0.26:0.74). On the basis of the solubility data, oxobasicity indices of the above melts were estimated as 4.05, 1.95, 2.01 and 1.83, respectively. The CaC1 2-based melt possesses the upper limit of oxobasicity at p O∼1.3 caused by the precipitation of CaO. The features of calibration plots E–p O in the studied melts are discussed.

Electron-irradiation-induced phase segregation in crystalline and amorphous apatite; a TEM study

Single crystals of natural F-rich apatite and 800 keV Kr (super 2+) ion-beam-amorphized apatite were irradiated by an electron beam in a transmission electron microscope over a range of beam energies and beam currents. Irradiation of crystalline apatite using a high current density (16 A/cm 2 ), caused the precipitation of cubic CaO from the crystalline apatite matrix. Using a lower beam current (1.6 A/cm 2 ), the formation of nanometer-sized voids was observed, but CaO did not crystallize even after prolonged irradiation. Amorphous apatite crystallized to a coarse-grained polycrystalline assemblage of apatite crystallites at 85-200 keV. Increasing the beam current through the sample caused the formation of finegrained cubic CaO, and the crystallization of apatite was not observed, even at high doses. In each case, many beam-induced bubbles formed and were typically larger at the edge of the beam. Thermal annealing at 450 degrees C resulted in epitaxial crystallization from the thick portions of the TEM foil and resulted in a single crystal with a high defect density. Electron-beam irradiations at 300 degrees C confirmed that the difference in microstructural evolution as a function of current density is driven by dose-rate effects. In fact, temperature and dose rate are competing effects in the precipitation of CaO.

Chemical Pulping of Straws (IV)

Among the countries using nonwood plant fiber as pulp raw materials, China is a leading country to use straw, reed, bamboo and so on (76.1% on total pulp ca. 10 million tons in 1992). However, the use of rice straw is quite small, because of a large amounts of ash, especially silica. Silica causes the scale trouble during the concentration of soda black liquor. Therefore, in order to use more rice straw for pulp production, silica trouble must be solved as soon as possible. On this point, it is also important to find the pulping method leaving silica in pulp.This paper presents the results of studies on the ash properties of straw and the behavior of rice straw ash in black liquor. The results are summarized as follows:(1) Crystalline structure of straw silica is the mixture of crystoballite and quartz type. It is interesting that the generated silica from sodium silicate in black liquor shows a diffuse, broad X-ray spectrum.(2) The ash in black liquor is removed by the addition of precipitant, namely CaO or CaO+CaCl2. The efficiency of CaCl2 addition is observed at the lower amounts of CaO addition (200% on silica) and shorter precipitation time (60 min. at 80°C). The efficiency of CaCl2 addition is not observed at higher CaO addition (300% on silica). The amounts of CaO precipitant and precipitation time can be decreased by the concentration of black liquor.(3) In order to remove separately ash and lignin in black liquor, two stage pH adjustments of black liquor are efficient.