Recovery of nano-calcium fluoride and ammonium bisulphate from phosphogypsum waste

ABSTRACT

The production of phosphoric acid generates an enormous amount of phosphogypsum with emission of toxic fluorine acid gas. To remedy these environmental problems, a novel and a simple procedure permits converting phosphogypsum waste by recycled fluorine acid into valuable products. The obtained results confirm the efficiency of this procedure, which synthesises at room temperature the calcium fluoride in the form of nano-crystalline powder and the ammonium bisulphate salt from the exact stoichiometric proportions of phosphogypsum, hydrofluoric acid and ammonia. The total conversion of phosphogypsum is achieved after reaction time equal to one hour and a half. Generally, this novel procedure offers not only a solution for reducing phosphogypsum waste and fluorine gas emission, but also gives rise to valuable products, useful to industry and agriculture.     

3D simulation of bolted connections to unstiffened columns-I. T-stub connections

The paper presents a finite element methodology in a three-dimensional (3D) framework to study numerically the stiffness and strength of the T-stub to unstiffened column flange bolted connection as part of a comprehensive research program to investigate the behavior of endplate bolted connections. In such connections, the axes of rotation of the T-stem and column flange are at right angles; the planes containing the tensile forces are also perpendicular to each other. Therefore, they are highly interactive spatially. The main objective here is to study the applicability of the model to such a connection, so that most of the important features which are not accessible to routine experiments, like prying action and gradual plasticity of components, can be monitored. ANSYS, version 4.4, a large-scale general purpose finite element code is selected for this analysis. Initially, the simplest connection with the bolt groups in tension, which is a symmetric T-stub hanger with a single line of bolts parallel on each side of the web, is considered. Then the T-stub connection to an unstiffened column flange is discussed. Analytical results of a full-scale extended endplate connected to unstiffened column flange will be presented in Part II, a companion paper (Journal of Constructional Steel Research, 1996, 40, 189–223) in which the structural properties of such connections will be discussed.     

Pentachlorophenol adsorption and desorption characteristics of granular activated carbon-I. Isotherms

The adsorption/desorption of pentachlorophenol (PCP) with Calgon F300 granular activated carbon (GAC) was studied and modelled. A modified Radke-Prausnitz (1972) isotherm model, incorporating a temperature- and pH-dependent proportionality constant, was found to best describe the observed PCP adsorption and desorption. The modified isotherm is valid in the ranges 4 ≤ pH ≤ 11 and 10 ≤ T ≤ 60°C. The activation energy of PCP adsorption was calculated to be 5.2 kJ/mol. At 30°C, PCP adsorbed strongly, and the rate of subsequent desorption was very low. However, the amount of PCP desorbed could be increased significantly by increasing the temperature to 60°C.     

Removal of chromium (VI) from aqueous solution using treated oil palm fibre

This study proposed an oil palm by-product as a low-cost adsorbent for the removal of hexavalent chromium [Cr (VI)] from aqueous solution. Adsorption of Cr (VI) by sulphuric acid and heat-treated oil palm fibre was conducted using batch tests. The influence of pH, contact time, initial chromium concentration and adsorbent dosage on the removal of Cr (VI) from the solutions was investigated. The optimum initial pH for maximum uptake of Cr (VI) from aqueous solution was found to be 1.5. The removal efficiency was found to correlate with the initial Cr (VI) concentration, adsorbent dosage as well as the contact time between Cr (VI) and the adsorbent. The adsorption kinetics tested with pseudo first order and pseudo second order models yielded high R(2) values from 0.9254 to 0.9870 and from 0.9936 to 0.9998, respectively. The analysis of variance (ANOVA) showed significant difference between the R(2) values of the two models at 99% confidence level. The Freundlich isotherm (R(2)=0.8778) described Cr (VI) adsorption slightly better than the Langmuir isotherm (R(2)=0.8715). Difficulty in desorption of Cr (VI) suggests the suitability of treated oil palm fibre as a single-use adsorbent for Cr (VI) removal from aqueous solution.     

Diclofenac-bismuth complex: synthesis, physicochemical, and biological evaluation

Diclofenac-bismuth complexation was attempted by mixing diclofenac sodium (Na) and bismuth-subcitrate aqueous solutions at diclofenac:bismuth molar ratio of 3:1. A solid precipitate was obtained and isolated. The precipitate was characterized for stoichiometric ratio of diclofenac-bismuth complexation using capillary electrophoresis, which showed 1:1 complexation. In addition, nuclear magnetic resonance and Fourier transform infrared analysis were performed for the isolated solid complex and indicated that bismuth was in coordinate bond formation with the carboxylate group of diclofenac. In comparison with diclofenac Na powder, the complex was evaluated as an aqueous suspension for in vitro drug dissolution. The complex exhibited a faster dissolution rate than and similar dissolution extent as diclofenac Na. In comparison with an aqueous solution of diclofenac Na and an aqueous suspension of physical mixture of diclofenac acid (suspended) and bismuth-subcitrate (dissolved), the aqueous complex suspension was evaluated for ulcerogenic effect in rats upon oral administration. The complex led to more gastric ulceration than diclofenac Na, which was not in accordance with the antiulcer properties of bismuth. This antiulcer effect was shown as the physical mixture administration was accompanied with lower gastric ulceration than diclofenac Na administration. These gastric ulceration results were explained in terms of the difference in particle size between solid diclofenac acid formed as a result of the complex breakdown in an acidic medium (0.1 M HCl to simulate the gastric fluid) and that formed as a result of diclofenac Na neutralization. Diclofenac acid particles formed from the complex breakdown were of average size, three times smaller of those formed as a result of diclofenac Na protonation. This difference in particle size was correlated with the higher gastric ulceration associated with the complex than with diclofenac Na in terms of higher coverage of the gastric mucosa with diclofenac, and consequently, higher local ulceration.     

Charge transport in grain size tuned CuO nanocrystal films

Journal of Electroceramics - CuO nanocrystal (NC) films of different grain sizes were synthesized through the oxidation of Cu films deposited by controlling the supersaturation in the deposition...     

Integrated ion exchange mixed bed with reverse osmosis and nanofiltration for isolation of neutral dissolved organic matter from natural waters

The aim of this study was to isolate the neutral dissolved organic matter (NDOM) and the low molecular weight neutrals (LMWN) from natural waters. The coupling of an ion exchange mixed bed (IEXMB) with reverse osmosis (RO) and nanofiltration was the main hypothesis. IEXMB removed charged species, while the neutral molecules were isolated in the demineralised water and then concentrated by RO without any osmotic pressure or fouling limits. Neutrals isolation and unlimited concentration, gives this paper its originality. The nanofiltration (NF) step allows for the isolation of the LMWN. The studied reservoir water NDOM and LMWN represented respectively 35% of the dissolved organic matter (DOM) and 34% of the NDOM. Aromatic compounds were found in both fractions. The UV254 absorbance measured before and after the IEXMB evidenced the water quality ‘signature’. IEX has never been studied as fractionation method of DOM. This IEXMB approach is thus quite novel.     

Biosynthesis of essential oils in aromatic plants: A review

In aromatic plants species, biosynthesis of essential oils occurs through two complex natural biochemical pathways involving different enzymatic reactions. Isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP) are the universal precursors of essential oil biosynthesis and are produced by the cytosolic enzymatic MVA (mevalonic acid) pathway or by plastidic and enzymatic 1-deoxy-d-xylolose-5-phosphate (DXP) pathway, also called the 2-C-methylerythritol-4-phosphate (MEP) pathway. In the particular plant cell part, prenyl diphosphate synthases condense isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) further to form prenyl diphosphates, which are used as substrates for geranyl diphosphate (GPP; C₁₀) or for fernesyl diphosphate (FPP; C₁₅). Essential oils are final terpenoid products and are formed by a huge group of enzymes known as terpene synthases (TPS). Essential oils are important secondary metabolites of plants and have been used not only in different industries but also in ethnobotanical medicines for centuries. Hence, considerable research has been undertaken to understand the essential oil biosynthetic pathways. This review will be a valuable source of information in the field of natural products, as we give detailed insights about biosynthesis of essential oils in plants and thus indicate also new unexplored horizons for further research.     

Near- and Far-Field Characterization of Planar mm-Wave Antenna Arrays with Waveguide-to-Microstrip Transition

We present the design and characterization of planar mm-wave patch antenna arrays with waveguide-to-microstrip transition using both near- and far-field methods. The arrays were designed for metrological assessment of error sources in antenna measurement. One antenna was designed for the automotive radar frequency range at 77 GHz, while another was designed for the frequency of 94 GHz, which is used, e.g., for imaging radar applications. In addition to the antennas, a simple transition from rectangular waveguide WR-10 to planar microstrip line on Rogers 3003? substrate has been designed based on probe coupling. For determination of the far-field radiation pattern of the antennas, we compare results from two different measurement methods to simulations. Both a far-field antenna measurement system and a planar near-field scanner with near-to-far-field transformation were used to determine the antenna diagrams. The fabricated antennas achieve a good matching and a good agreement between measured and simulated antenna diagrams. The results also show that the far-field scanner achieves more accurate measurement results with regard to simulations than the near-field scanner. The far-field antenna scanning system is built for metrological assessment and antenna calibration. The antennas are the first which were designed to be tested with the measurement system.