Kinetic study of ytterbium(III) extraction from sulfate medium with Cyanex 923

The kinetics of ytterbium(III) extraction from sulfate medium with Cyanex 923 in heptane has been investigated with a constant interfacial cell with laminar flow, which aimed to identify the extraction regime, reaction zone and rate equations. It was found that the extraction rate of ytterbium(III) increased linearly with stirring speed and specific interfacial area. The activation energy E_a (9.56 kJ mol^?1), activation enthalpy ΔH^± (7.05 kJ mol^?1), activation entropy ΔS^±₂₉₈ (?0.31 kJ mol^?1) and Gibbs free energy of activation ΔG^±₂₉₈ (98.3 kJ mol^?1) were calculated from the dependence of extraction rate on temperature. The experiential rate equations were obtained by investigating the influence of the concentration of various species on the extraction rate. A diffusion regime has been deduced from evidence of the linear dependence of extraction rate on stirring speed and the low value of the activation energy. The liquid–liquid interface is most probably the reaction zone in view of the linear dependence of extraction rate on specific interfacial area, the high interfacial activity and low water‐solubility of extractant. Thus the mass transfer rate is controlled by interfacial film diffusion of species. Copyright © 2007 Society of Chemical Industry     

Extraction kinetics of cerium(IV) from sulfuric acid medium by the primary amine N1923 using a constant interfacial area cell with laminar flow

BACKGROUND: Thermodynamic studies on Ce(IV) extraction with primary amine N1923 demonstrate that primary amine N1923 is an excellent extractant for separation of Ce(IV) from Re(III). In order to clarify the mechanism of extraction and to optimize the parameters in practical extraction systems used in the rare earth industry, the extraction kinetics was investigated using a constant interfacial area cell with laminar flow in the present work. RESULTS: The data indicate that the rate constant (k_ao) becomes constant when stirring speed exceeds 250 rpm. The apparent forward extraction rate is calculated to be 10^?1.70. The activation energy (E_a) was calculated to be 20.5 kJ/mol from the slope of log k_ao against 1000/T. The minimum bulk concentration of the extractant necessary to saturate the interface (C_min) is lower than 10^?5 mol L^?1. CONCLUSION: Studies of interfacial tension and the effects of stirring rate and specific interfacial area on the extraction rate show that the extraction rate is kinetically controlled, and a mass transfer model has been proposed. The rate equation has been obtained as: ? d[Ce(IV)]/dt = 10^?1.70[Ce(IV)] [(RNH₃)₂SO₄]^1.376. The rate‐controlling step has been evaluated from analysis of the experimental results. Copyright © 2007 Society of Chemical Industry     

Mass transfer kinetics of neodymium(III) extraction by calix[4]arene carboxylic acid using a constant interfacial area cell with laminar flow

BACKGROUND: Thermodynamics and kinetics data are both important to explain the extraction property. In order to develop a novel separation technology superior to current extraction systems, many promising extractants have been developed including calixarene carboxylic acids. The extraction thermodynamics behavior of calix[4]arene carboxylic acids has been reported extensively. In this study, the mass transfer kinetics of neodymium(III) and the interfacial behavior of calix[4]arene carboxylic acid were investigated. RESULTS: The rate constant (K_ao) becomes constant when the stirring speed was controlled between 250 rpm and 400 rpm. The activation energy (E_a) was calculated to be 21·41 kJ mol^?1 or 88·17 kJ mol^?1 (dependent on temperature) from the slope of log K_ao against 1000/T. The linear relationship between the specific area and the extraction rate is the characteristic of an interfacial reaction control. The minimum bulk concentration of the extractant necessary to saturate the interface (C_min) is lower than 4·19 × 10^?4 mol L^?1. CONCLUSION: The effect of stirring speed, temperature, and species concentration on the extraction rate demonstrates that the extraction regime depends on the extraction conditions. The chemical reaction control governs the extraction regime at temperatures below 303 K and a mixed control regime occurs when the temperature is between 303 K and 318 K. The probable locale for the chemical reaction is at the liquid–liquid interface and the rate equation is deduced to be: ? d[Nd³⁺]_(a)/dt = k_f[Nd³⁺]_(a)[H₄A]_(o)^0·727[H⁺]_(a)^?0·978. The rate‐controlling step was suggested by the analysis of the experimental results. Copyright © 2008 Society of Chemical Industry     

Factorial Design Optimization of Solid-Phase Microextraction for High-Performance Liquid Chromatography−Ultraviolet Spectrometry Analysis of Polycyclic Aromatic Hydrocarbons in Cigarette Filter Tar

A simple and rapid procedure for the determination of polycyclic aromatic hydrocarbons (PAHs) in cigarette filter tar using solid-phase microextraction (SPME) was developed. The analysis was carried out using high-performance liquid chromatography equipped with an ultraviolet detector. The effects of the SPME experimental parameters on the extraction recovery were studied simultaneously using a central composite design (CCD) after a 2^6?2 fractional factorial experimental design. The SPME variables of interest were the extraction temperature, the extraction time, and the stirring speed, as well as the pH and the concentrations of NaCl (%, w/v) and acetonitrile (ACN). The optimal SPME conditions were as follows: an extraction temperature of 65°C, an extraction time of 50 min, a stirring speed of 800 rpm, 0% NaCl (w/v), 10% ACN in the sample, and a source pH of 8.0. The extraction calibration plots were linear over the range of 0.25?20 ng mL^?1 (r² > 0.9912) and the limits of detection (LODs) for the 6 PAHs studied were from 0.17–5.02 ng cigarette^?1. The relative standard deviation (RSD) ranged from 7.1–13.5% for intra-day variation and from 8.5–18.4% for inter-day variation. The performance of the proposed method was evaluated for extraction and determination PAHs in real samples (various brands of cigarettes). The total amounts of all of the studied PAHs found in the filter tar of the three brands of cigarettes were 320.2, 17.9, and 66.7 ng cigarette^?1, respectively.     

Effect of Bismuth substitution on the enhancement of thermoelectric power factor of nanostructured BixCo3-xO4

Bismuth Cobalt Oxide (Bi_xCo_3-xO₄) nanoparticles with different compositions (x?=?0, 0.025, 0.05, 0.1, 0.2) were prepared by chemical precipitation method. The structural, morphological and thermal properties of the prepared samples were studied by XRD, SEM, FTIR and TG&DTA analysis. X-ray diffraction analysis shows that pure phase of Cobalt oxide was formed till x?≤?0.05 and while increasing the Bi concentration (0.05?≤ x?≤?0.2) mixed phases of Co₃O₄, Co₂O₃, CoO and separate phase of Bi₂O₃ were formed. The diffraction peaks were reasonably shifted due to substitution of Bi²⁺ ions. XPS analysis conforms the presence of mixed valance states of Co and presence of Bi with their binding states in the samples. The electrical resistivity and Seebeck coefficient were measured for Bi_xCo_3-xO₄ (0?≤ x?≤?0.2) at different temperatures. It was observed that the electrical resistivity decrease till x?≤?0.05 due to the substitution of Bi ions in Cobalt lattice and increases at higher x values (0.05?≤ x?≤?0.2) due to the formation of Bi₂O₃ phase. The Bi substitution has considerably reduced the electrical resistivity by one order when completely dissolved in the cobalt oxide lattice at lower x values. The Seebeck coefficient value gradually increased for all samples of Bi_xCo_3-xO₄ (0?≤ x?≤?0.2). The power factor was calculated from electrical resistivity and Seebeck coefficient and the maximum power factor of 0.025 µWm^?1K^?2 was obtained for Bi_0.2Co_2.8O₄ sample at 530?K. The experimental results revealed that the Bi substitution have promising effect on the thermoelectric properties of nanostructured Bi_xCo_3-xO₄ (0?≤ x?≤?0.2).     

Improved photocatalytic performance in Bi2S3-ZnSe nanocomposites for hydrogen production

One way to improve the rate of hydrogen production from water-splitting reactions is by the separation of photogenerated carriers. This separation process can be achieved with narrow bandgap semiconductors. ZnSe has a 2.7?eV bandgap, but its photocatalytic activity is very low due to a high recombination rate of the photogenerated carriers. Therefore, a combination of Bi₂S₃ and ZnSe may potentially produce a visible-light-active photocatalyst, utilizing bandgap engineering and the p-n junction effect. ZnSe, Bi₂S₃ and Bi₂S₃-ZnSe nanocomposites were prepared by a hydrothermal method. Bi₂S₃ at different weight percentages (3–15?wt%) was decorated with ZnSe nanoparticles. The hydrogen evolution reaction was conducted in the investigation of ZnSe, Bi₂S₃ and Bi₂S₃-ZnSe photocatalytic efficiency. The results demonstrate that photocatalytic efficiency was highly affected by the Bi₂S₃ weight percent. The optimal weight percent for Bi₂S₃ was 15?wt%, at which the rate of hydrogen evolution was 2600?μmol?g^?1 h^?1 within 240?min in the presence of 1.2?g/L photocatalyst.     

Influence of Ba2+ doping on the thermoelectric properties of BiCuSeO fabricated by spark plasma sintering

We studied the influence of Ba²⁺ doping on the thermoelectric properties of the p-type Bi_1–xBa_xCuSeO (0?≤?x?≤?0.21) fabricated by spark plasma sintering. The substitution of Ba²⁺ for Bi³⁺ gradually increased the electrical and thermal conductivities and decreased the Seebeck coefficient, which were due to the increased hole concentration. The largest value of dimensionless figure-of-merit (0.57) was obtained for the Bi_0.86Ba_0.14CuSeO at 500?°C, which was over three times greater than that of pristine BiCuSeO (0.18) at 500?°C. We believe that the thermoelectric properties of BiCuSeO were substantially enhanced through the partial substitution of Ba²⁺ for Bi³⁺.     

Kinetic Study for Biphasic Recognition Chiral Extraction of Naproxen Enantiomers with Hydrophobic L-iso-butyl Tartrate and Hydrophilic Hydroxypropyl-β-Cyclodextrin

The kinetics of biphasic recognition chiral extraction of naproxen (HA) enantiomers was investigated to determine the extraction mechanism, with hydrophobic L-iso-butyl tartrate (L-IBTA) in the organic phase and hydrophilic hydroxypropyl-β-cyclodextrin (HP--CD) in the aqueous phase. The two-phase homogeneous reaction model was selected over the interfacial reaction model, because there is a clear physical solubility of naproxen enantiomers in both the aqueous phase and the organic phase. The reactions between the HA enantiomers and L-iso-butyl tartrate in a stirred cell fall in Regime 3; the extraction is accompanied by two fast chemical reactions in the diffusion film. The reactions have been found to be first order with respect to HA enantiomers and second order with respect to L-IBTA. The forward rate constants for S-HA and R-HA are 1.26?×?10^?4 mol^?2 m⁶ s^?1 and 2.52?×?10^?4 mol^?2 m⁶ s^?1, respectively. With the increase of HP--CD concentration in the aqueous phase, high enantioselectivity was obtained, but the extraction rates decreased. These data will be useful in the design of extraction processes.     

IMPACT OF THE LOW-TEMPERATURE REACTIVITY OF REILLEX™ HPQ ON ACTINIDE PROCESSING

ABSTRACT

Reactive System Screening Tool^? data and a computational model were used to predict the impact of pressurization on a typical process-scale ion exchange column due to gases generated by the low temperature exothermic reaction (LTE). The LTE results from a reaction between nitric acid and the ethylbenzene pendant groups of the Reillex^? HPQ resin. This reaction would occur if the resin bed were inadvertently heated above 70?C. Without accounting for heat transfer, activation of the LTE at 70?C would result in a calculated maximum temperature of 106?C, which is below the boiling point of 8?M nitric acid (112?C), and well below the temperatures leading to runaway reaction (～145?C). A pressure drop calculation shows that if a typical process-scale ion exchange column of Reillex^? HPQ is inadvertently heated to activate the LTE, the resulting pressurization (ΔP=0.37?psi) could be dissipated safely via a 0.5-inch ever-open vent without challenging a 60-psi?g rupture disk.     

Dielectric,ferroelectric, and energy storage properties in dysprosium doped sodium bismuth titanate ceramics

In this work, Na_0.5(Bi_1-xDy_x)_0.5TiO₃ (0?≤?x?≤?15%) ceramics were prepared via solid state reaction method and were characterized. A stable and pure perovskite phase was revealed by X-ray diffraction analysis for all compositions and a symmetry change from rhombohedral to orthorhombic phase was detected beyond 10% of Dy substitution. The incorporation of Dy³⁺ into Sodium Bismuth Titanate (Na_0.5Bi_0.5TiO₃) matrix allows a substantial decrease of the coercive field, an increase in the resistivity, and leads to a high stability of the dielectric permittivity (??/?_(150?°C) ≤?±?15%) over a wide temperature range. Furthermore, this system was found to exhibit improved energy storage properties at high temperatures with a maximum energy density of 1.2?J/cm³ obtained for 2%Dy composition at 200?°C. The obtained results are very promising for energy storage capacitors operating at high temperatures.     

Performance of an RTL contactor for gas-liquid systems: Effective interfacial area and volumetric mass transfer coefficient by oxidation of sodium sulphite solution

Effective interfacial area a and volumetric liquid-side mass transfer coefficient k_La of an RTL contactor were obtained at different stirring speeds by absorption of oxygen from air into 0.8 kmol/m³ sodium sulphite solution, in the presence of Co⁺⁺ ions. The values of a and k_La ranged from 80 to 150 m²/m³ and 0.0003 to 0.00053 s^?1, respectively, when stirrer speed was increased from 8 to 40 rpm. When k_L alone was evaluated, it was found to be practically constant, irrespective of stirring speed.     

Ultrafiltration of Hematite Sol

Abstract

Ultrafiltration of a laboratory-made hematite sol was studied in a batch cell with an Amicon PM 10 membrane at 298 K. The effects of hematite bulk concentrations (2 to 10 kg·m^?3), stirring conditions (0 and 400 rpm), and pressure (50 to 350 kPa) were investigated. The permeate flux increases with increasing pressure and stirrer speed, and decreases with increasing hematite bulk concentration. The polarization resistance increases with an increase in pressure and hematite concentration. The polarization resistance is greater under unstirred conditions.     

Bismuth sulfide and its carbon nanocomposite for rechargeable lithium-ion batteries

Bi₂S₃ and Bi₂S₃/C nanocomposites prepared by high-energy mechanical milling were evaluated as electrode materials in lithium secondary batteries. For a Bi₂S₃/C nanocomposite, Bi₂S₃ nanocrystallites were well distributed in an amorphous carbon matrix. The reaction mechanism of the Bi₂S₃/C electrode was also examined during the first cycle. The Bi₂S₃/C nanocomposite anode showed superior electrochemical performance (ca. 500 mAh g⁻¹ and 85% of the capacity retention over 100 cycles).     

Effect of particle size on thermal decomposition and devolatilization kinetics of melon seed shell

Thermogravimetric analysis (TGA) and devolatilization kinetics of melon seed shell (MSS) at different particle sizes (150?µm and 500?µm) and at different heating rates (10, 15, 20, and 25?°C/min) were investigated with the aid of TGA. The results of the TGA analysis show that the TGA curves corresponding to the first and third stages for 150?µm particle sizes exhibited some bumps that developed at the first and third stages of pyrolysis. It was also observed that at constant heating rate, the maximum peak temperature increases as the particle sizes increase from 150 to 500?µm, whereas 500?µm particle sizes exhibited higher peak temperatures compared to 150?µm particle sizes. The resulting TGA data were applied to the Kissinger (K), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods and kinetic parameters (activation energy, E and frequency factor, A) were determined. The E and A obtained using K method were 74.27?kJ mol^?1 and 3.84?×?10⁵?min^?1 for 150?µm particle size, whereas for 500?µm particle size were 97.12?kJ mol^?1 and 3.74?×?10⁷?min^?1, respectively. However, the average E and A obtained using KAS and FWO methods were 82.35?kJ mol^?1, 1.29?×?10⁷?min^?1, and 88.50?kJ mol^?1, 1.32?×?10⁷?min^?1 for 150?µm particle sizes. While for 500?µm particle sizes, the E and A were 108.46?kJ mol^?1, 3.14?×?10⁹?min^?1, and 113.05?kJ mol^?1, 7.56?×?10⁹?min^?1, respectively. It was observed that E and A calculated from FWO and KAS methods were very close and higher than that obtained by K method. It was observed that the minimum heat required for the cracking of MSS particles into products is reached later at higher peak temperatures since the heat transfer is less effective as they are at lower peak temperatures.     

Reduction of hexavalent chromium by Bacillus sp. isolated from chromite mine soils and characterization of reduced product

BACKGROUND: The reduction of highly mobile and toxic hexavalent chromium by bacterial strains is considered to be a viable alternative to reduce Cr(VI) contamination, in soils and water bodies, emanating from the overburden dumps of chromite ores and mine drainage. The present study reports the isolation of Cr(VI) resistant bacterial strains from an Indian chromite mine soil and their potential use in reduction of hexavalent chromium. RESULTS: Among the isolates, a bacterial strain (CSB‐4) was identified as Bacillus sp. based on standard biochemical tests and partial 16SrRNA gene sequencing, which was tolerant to as high as 2000 mg L^?1 Cr(VI) concentration. The strain was capable of reducing Cr(VI) to Cr(III) in different growth media. Under the optimized conditions pH ～7.0, 100 mg L^?1 Cr(VI), 35 °C temperature and stirring speed 100 rpm, CSB‐4 reduced more than 90% of Cr(VI) in 144 h. The time course reduction data fitted well an exponential rate equation yielding rate constants in the range 3.22 × 10^?2 to 6.5 × 10^?3 h^?1 for Cr(VI) concentration of 10–500 mg L^?1. The activation energy derived from temperature dependence rate constants between 25 and 35 °C was found to be 99 kJ mol^?1. The characterization of reduced product associated with bacterial cells by SEM‐EDS, FT‐IR and XRD was also reported. CONCLUSION: Reasonably high tolerance and reduction ability of indigenous Bacillus sp. (CSB‐4) for Cr(VI) under a wide range of experimental conditions show promise for its possible use in reclamation of chromite ore mine areas including soils and water bodies. Copyright © 2010 Society of Chemical Industry     

Bismuth metal–organic frameworks derived bismuth selenide nanosheets/nitrogen–doped carbon hybrids as anodes for Li–ion batteries with improved cyclic performance

Nanohybrids have significant potential in improving the performance of Li–ion batteries (LIBs). Herein, bismuth selenide nanosheets/nitrogen–doped carbon hybrids (Bi₂Se₃@NC) are prepared by selenylation of bismuth (III) metal–organic frameworks (Bi–MOFs), which are obtained by solvothermal reaction in a mixed solvent of N, N–dimethylformamide and methanol. When served as anodes for Li–ion batteries, it was found that the post–treatment temperature of Bi–MOFs has a powerful impact on Li storage performance. Compared to Bi₂Se₃@NC–500 and Bi₂Se₃@NC–600 hybrids, Bi₂Se₃@NC–400 hybrids deliver large specific capacity, outstanding rate performance, and good cyclic stability. 410.6 mAh g^?1 of capacity is gained after 50 cycles at 100?mA?g^?1. Even at 500?mA?g^?1, 335.8 mAh g^?1 is achieved after 400 cycles. The superior Li storage feature of Bi₂Se₃@NC–400 hybrids is ascribed to the synergetic effect between Bi₂Se₃ nanosheets and N–doped nanocarbon. Bi₂Se₃@NC–400 hybrids is a promising anode material for LIBs.     

Leaching kinetics of colemanite in ammonium hydrogen sulphate solutions

The aim of the study was to investigate the dissolution kinetics of colemanite in ammonium hydrogen sulphate solutions in a mechanical agitation system and to declare an alternative reactant to produce boric acid. Reaction temperature, concentration of ammonium hydrogen sulphate, stirring speed, solid/liquid ratio and particle size were selected as parameters on the dissolution rate of colemanite. The experimental results were successfully correlated by linear regression using Statistica Package Program. Dissolution curves were evaluated in order to test shrinking core models for solid–fluid systems. It was observed that increase in the reaction temperature and decrease in the solid/liquid ratio causes an increase the dissolution rate of colemanite. The dissolution extent is highly increased with increase the stirring speed rate between 100 and 500 rpm and the dissolution extent is slowly increased with increase the stirring speed between 500 and 700 rpm in experimental conditions. The activation energy was found to be 32.66 kJ/mol. The leaching of colemanite was controlled by diffusion through the ash or product layer. The rate expression associated with the dissolution rate of colemanite depending on the parameters chosen may be summarized as follows: 1 ? 3(1 ? X)^2/3 + 2(1 ? X) = 8.99 × C^1.08 × W^1.39 × D^?1.27 × (S/L)^?0.54 × e^(?32.66/RT)t.     

Removal of suspended solids and residual oil from palm oil mill effluent

Palm oil mill effluent (POME) was pretreated to remove suspended solids and residual oil. The processes used were flocculation, solvent extraction, adsorption and membrane separation. Flocculation was used to remove suspended solids, and solvent extraction and adsorption processes were used to remove residual oil. Membrane separation was subsequently applied to remove any residual suspended solids and oil remaining after the pretreatments. The solvent extraction and adsorption processes were operated on a batch basis whereas membrane separation was performed in continuous mode. The treatment efficiency of the processes was measured as percentage removal of suspended solids and oil respectively. The optimum values of the process parameters obtained in the flocculation process were an alum dosage of 4000 mg dm^?3, mixing speed of 150 rpm for 1 h and sedimentation time of 270 min, resulting in 93% suspended solids removal. In the solvent extraction process, a 95% reduction in residual oil was obtained using n‐hexane as a solvent with 20 min of mixing at 200 rpm. The ratio of solvent to POME was 6:10 and carried out at pH 9. In the batch adsorption process, an 88% reduction in residual oil was obtained at a mixing speed of 100 rpm for 1 h, pH 9 and an adsorbent dosage of 300 g dm^?3. In membrane separation processes, GH and CE(GH) membranes gave 63% and 49% reductions in suspended solids and residual oil respectively at pH 9 and pressure of 1000 kPa. Copyright © 2003 Society of Chemical Industry     

Thermoelectric properties of Bi2O3-added WO3 ceramics

Tungsten trioxide (WO₃) ceramics were prepared by firing Bi₂O₃-added WO₃ compacts with atomic ratios of Bi/W?=?0.00, 0.01, 0.03, or 0.05, in which Bi₂O₃ was mixed as a sintering agent. Dense ceramics consisting of remarkably grown WO₃ grains were obtained for Bi-containing samples with Bi/W?=?0.01, 0.03, and 0.05. The grain growth was enhanced by the liquid phase of Bi₂W₂O₉ formed among the WO₃ grains while firing. The XRD patterns did not show evidence for Bi inclusion into the WO₃ lattice, but the SEM-EDX showed an intensive distribution of Bi into the grain boundaries. Electrical conductivity σ and Seebeck coefficient S were measured in a temperature range of 373–1073?K. The temperature dependences indicated that the Bi₂O₃-added WO₃ ceramics were n-type semiconductors. It was considered that the electron carriers were generated from oxygen vacancies included into the WO₃ grains. The thermoelectric power factors S²σ for the ceramics ranged from 1.5?×?10^?7 W?m^?1 K^?2 to 2.8?×?10^?5 W?m^?1 K^?2, and the highest value occurred at 970?K for the ceramic with Bi/W?=?0.01.     

Synthesis,structural, electrical and magnetic properties of Bi2Fe4-xGaxO9 (0 ≤ x ≤ 1.6)

We investigate the electrical and magnetic properties of the Bi₂Fe_4-xGa_xO₉ (0?≤?x?≤?1.6) polycrystalline samples synthesized via solid-state reaction technique. Magnetic susceptibility measurements reveal that lightly doped samples (x?<?0.8) undergo successive transitions, from high-temperature paramagnetic to antiferromagnetic phase followed by a low-temperature spin-glass state while the samples with heavy doping (x?>?0.8) demonstrate paramagnetic to spin-glass (SG) transition. The variation of irreversible temperature obtained from zero field cooling (ZFC) and field cooling (FC) susceptibilities versus measured magnetic field and low-temperature magnetic hysteresis (M-H) loops support the existence of spin-glass phase. The dielectric constant (?_r) of Bi₂Fe_4-xGa_xO₉ with Ga-dilution reveals a weak-temperature sensitivity in high-temperature range (300?K?≤?T?≤?550?K), which is advantageous for high temperature capacitor applications and electronic devices.