A kinetic investigation of removal of chromium from aqueous solutions with a strong cation exchange resin

A kinetic investigation was performed with an ion exchange resin for chromium. A strong cation exchange resin (Amberlite IR 120) was used for removal of chromium. The effects of concentration, resin amount, and stirring speed on kinetics were investigated. The metal concentration range studied was between 5 to 160 mg/dm³ (the amount of solution was 4 dm³), the resin amount range was between 5 to 20 mg, and the stirring speed range was between 1000 to 3500 rpm. Equilibrium experiments were performed for calculation of separation factor. Kinetic studies were done using a Kressman-Kitchener stirrer reactor system and the results were compared with existing kinetic models. Two models, Nernst-Plank film diffusion control model (fdc) and solid phase diffusion control model (pdc), respectively were identified, and the dependence of the rate on parameters such as solution concentration, resin amount, stirring speed, etc. was examined for each of them. The interpretation of these data shows that the system is probably controlled by both film and particle diffusion. Correspondence: Sevgi Kocaoba, Department of Chemistry, Faculty of Art and Science, Yildiz Technical University, Davutpasa Cad. No: 127, 34210 Davutpasa-Istanbul, Turkey.     

On approximations of the de Rham complex and their cohomology

For a commutative algebra R, its de Rham cohomology is an important invariant of R. In the paper, an infinite chain of de Rham-like complexes is introduced where the first member of the chain is the de Rham complex. The complexes are called approximations of the de Rham complex. Their cohomologies are found for polynomial rings and algebras of power series over a field of characteristic zero.     

Removal and recovery of chromium and chromium speciation with MINTEQA2

Chromium(III) is commonly found in large quantities in tannery wastewaters. For this reason, the recovery of the chromium content of these wastewaters is necessary for environmental protection and economic reasons. Removal and recovery of chromium were carried out by using ion exchange resins. To this purpose, two weakly acidic exchange resins Amberlite IRC 76 and Amberlite IRC 718 and a strongly acidic exchange resin Amberlite IR 120 were used. Basic chromium sulphate [Cr(4)(SO(4))(5)(OH)(2)] solutions in different concentrations and pH were used in all experiments as tanning baths. The resins were prepared in two different ionic forms as Na(+) and H(+). The effects of concentration, pH, stirring time and resin amount were investigated. The concentration range varied between 5 and 100 mg l(-1), pH range was between 1 and 8, stirring time between 5 and 60, and resin amount was between 50 and 1000 mg. Stirring speed was 2000 rpm during all these experiments. Exchange capacities, moisture contents and optimum conditions of these resins were determined in batch system. The results obtained showed that Amberlite IRC 76 and 718 weakly acidic resins had shown better performance than Amberlite IR 120 strongly acidic resin for removal and recovery of chromium(III) in Na(+) form. Optimum conditions were found as concentration 10 mg l(-1), pH 5, stirring time 20 min, and resin amount 250 mg. Furthermore, chromium(III) speciation was investigated for optimum concentration and pH with MINTEQA2 computer programme. The studied pH range was between 1 and 8 and concentration range was between 5 and 100 mg l(-1). Cr(OH)(2+) species were found to be dominant at pH 5 and 10 mg l(-1) concentration in batch studies. There was a correlation between experimental and computerised results.     

Analysis of 2-D motion tracking in ultrasound with dual transducers

We study displacement and strain measurement error of dual transducers (two linear arrays, aligned orthogonally and coplanar). Displacements along the beam of each transducer are used to obtain measurements in two-dimensions. Simulations (5 MHz) and experiments (10 MHz) are compared to measurements with a single linear array, with and without angular compounding. Translation simulations demonstrate factors of 1.07 larger and 8.0 smaller biases in the axial and lateral directions respectively, for dual transducers compared to angular compounding. As the angle between dual transducers decreases from 90° to 40°, for 1% compression simulations, the lateral RMS error ranges from 2.1 to 3.9 μm compared to 9 μm with angular compounding. Simulation of dual transducer misalignment of 1 mm and 2° result in errors of less than 9 μm. Experiments demonstrate factors of 3.0 and 5.2 lower biases for dual transducers in the axial and lateral directions respectively compared to angular compounding.     

Reversed-phase HPLC analysis of levetiracetam in tablets using monolithic and conventional C18 silica columns

Development and validation of an RP-HPLC method for determination of levetiracetam in pharmaceutical tablets is described. The separation and quantification of levetiracetam and caffeine (internal standard) were performed using a single analytical procedure with two different types of stationary phases, conventional Phenomenex Gemini C18 (100 x 4.6 mm, 5 microm) and Merck Chromolith Performance RP18e (100 x 4.6 mm, macropore size 2 mm, micropore size 13 nm) monolithic silica. Five-microliter aliquots of samples were injected into the system and eluted using water-acetonitrile (90 + 10, v/v) mobile phase pumped at the rate of 1 mL/min. The analyte peaks were detected at 200 nm using a diode array detector with adequate resolution. Validation studies were performed using the method recommended by the International Conference on Harmonization, the U.S. Pharmacopeia, and AOAC INTERNATIONAL, which includes accuracy, precision, range, limits, robustness, and system suitability parameters. Levetiracetam and caffeine were detected in about 7 min using the conventional column, whereas less than 5 min was required when the monolithic column was used. Calibration plots had r values close to unity in the range of 0.8-8.0 microg/mL. Assay of levetiracetam in a tablet formulation was demonstrated as an application to real samples.     

Biosorption of Au (III) and Cu (II) from aqueous solution by a non-living Cetraria islandica (L.) Ach

Biosorption of Au(III) and Cu(II) from dilute aqueous solutions was investigated by biomass of the non-living Cetraria islandica (L.) Ach. The removal and recovery of gold and copper were studied by applying batch technique. The experimental parameters such as the pH of the solution, contact time, the amount of Cetraria islandica (L.) Ach. (dried lichen), the concentration of metals on retention and eluents kind and amount have been investigated. Au(III) and Cu(II) were adsorbed on the dried lichen at pH 3 and pH 8, respectively. Quantitative retention (> or = 90%) was obtained within 60 minutes for metals. Maximum capacity of 1.0 g of dried lichen for biosorption of Au(III) and Cu(II) were found as 7.4 mg of Au(III) and 19.2 mg of Cu(II). It was seen that the adsorption equilibrium data conformed well to the Langmuir model and Freundlich equation for Au(III) and only Freundlich equation for Cu(II). The method proposed in this study was applied to spiked mineral water analysis and metals adsorbed on the lichens were quantitatively (> or = 90%) recovered from mineral water samples by using 0.5 mol L(-1) HCl.     

A kinetic investigation of removal of chromium from aqueous solutions with a strong cation exchange resin

A kinetic investigation was performed with an ion exchange resin for chromium. A strong cation exchange resin (Amberlite IR 120) was used for removal of chromium. The effects of concentration, resin amount, and stirring speed on kinetics were investigated. The metal concentration range studied was between 5 to 160 mg/dm³ (the amount of solution was 4 dm³), the resin amount range was between 5 to 20 mg, and the stirring speed range was between 1000 to 3500 rpm. Equilibrium experiments were performed for calculation of separation factor. Kinetic studies were done using a Kressman-Kitchener stirrer reactor system and the results were compared with existing kinetic models. Two models, Nernst-Plank film diffusion control model (fdc) and solid phase diffusion control model (pdc), respectively were identified, and the dependence of the rate on parameters such as solution concentration, resin amount, stirring speed, etc. was examined for each of them. The interpretation of these data shows that the system is probably controlled by both film and particle diffusion.     

Treatment of opium alkaloid containing wastewater in sequencing batch reactor (SBR)—Effect of gamma irradiation

Aerobic biological treatment of opium alkaloid containing wastewater as well as the effect of gamma irradiation as pre-treatment was investigated. Biodegradability of raw wastewater was assessed in aerobic batch reactors and was found highly biodegradable (83–90% degradation). The effect of irradiation (40 and 140 kGy) on biodegradability was also evaluated in terms of BOD₅/COD values and results revealed that irradiation imparted no further enhancement in the biodegradability. Despite the highly biodegradable nature of wastewater, further experiments in sequencing batch reactors (SBR) revealed that the treatment operation was not possible due to sludge settleability problem observed beyond an influent COD value of 2000 mg dm^?3. Possible reasons for this problem were investigated, and the high molecular weight, large size and aromatic structure of the organic pollutants present in wastewater was thought to contribute to poor settleability. Initial efforts to solve this problem by modifying the operational conditions, such as SRT reduction, failed. However, further operational modifications including addition of phosphate buffer cured the settleability problem and influent COD was increased up to 5000 mg dm^?3. Significant COD removal efficiencies (>70%) were obtained in both SBRs fed with original and irradiated wastewaters (by 40 kGy). However, pre-irradiated wastewater provided complete thebain removal and a better settling sludge, which was thought due to degradation of complex structure by radiation application. Degradation of the structure was observed by GC/MS analyses and enhancement in filterability tests.     

A Kinetic Investigation of Chromium

A kinetic investigation was performed with an ion exchange resin for chromium. A chelating cation exchange resin (Amberlite IRC 718) was used for removal and recovery of chromium. The effect of concentration, resin amount, particle size and stirring speed on kinetics were investigated. The metal concentration range studied was between 5 to 160 mg L^–1, the resin amount range was between 5 to 20 mg, the particle size range was between 0.35 to 1.8 mm and the stirring speed range was between 1000 to 3500 rpm.Kinetic studies were done using a Kressman-Kitchener stirrer reactor system and the results were compared with existing kinetic models. Two models; Nernst-Plank film diffusion control model (fdc) and solid phase diffusion control model (pdc) were identified and the dependence of the rate on parameters, such as solution concentration, particle size, resin amount, stirring speed, etc., was examined for each of them. As a result, interpretation of these data showed that the system is probably controlled both film and particle diffusion.     

A new approach to the integrated calibration in flow injection analysis

A new proposal how to perform the analytical procedure according to the integrated calibration method is presented. An original flow injection system has been designed for this purpose. When using only a single standard solution, the measurement information gathered during a single analytical course permits construction of four calibration graphs and calculation of as many as four independent estimations of the analyte concentration in the sample examined. As the calibration method applied integrates the set of standards method and the standard addition method, the analytical estimations may be obtained in both the interpolative and the extrapolative manner and the final result can be effectively verified in terms of accuracy. The system developed was experimentally tested on the example of spectrophotometric determination of chromium. It has been proved to be capable of saving time and reagents as well as providing reliable analytical results. Owing to the instrumental simplicity and analytical efficiency the system is expected to be useful for routine analysis.