Solid phase extraction of chromium(VI) from aqueous solutions by adsorption of its diphenylcarbazide complex on a mixed bed adsorbent (acid activated montmorillonite-silica gel) column.
ABSTRACT A novel approach has been developed for the solid phase extraction of chromium(VI) based on the adsorption of its diphenylcarbazide complex on a mixture of acid activated montmorillonite (AAM)-silica gel column. The effect of various parameters such as acidity, stability of the column, sample volume, interfering ions, etc., were studied in detail. The adsorbed complex could be easily eluted using polyethylene glycol-sulfuric acid mixture and the concentration of chromium has been determined using visible spectrophotometry. The calibration graph was linear in the range 0-1microgmL(-1) chromium(VI) with a detection limit of 6microgL(-1). A highest preconcentration factor of 25 could be obtained for 250mL sample volume using glass wool as support for the mixed bed adsorbent. Chromium(VI) could be effectively separated from other ions such as nickel, copper, zinc, chloride, sulfate, nitrate, etc., and the method has been successfully applied to study the recovery of chromium in electroplating waste water and spiked water samples.
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ABSTRACT: A sensitive and simple method for determination of chromium species after separation and preconcentration by solid phase extraction (SPE) has been developed. For the determination of the total concentration of chromium in solution, Cr(VI) was efficiently reduced to Cr(III) by addition of hydroxylamine and Cr(III) was preconcentrated on a column of immobilised ferron on alumina. The adsorbed analyte was then eluted with 5 mL of hydrochloric acid and was determined by flame atomic absorption spectrometery. The speciation of chromium was affected by first passing the solution through an acidic alumina column which retained Cr(VI) and then Cr(III) was preconcentrated by immobilised ferron column and determined by FAAS. The concentration of Cr(VI) was determined from the difference of concentration of total chromium and Cr(III). The effect of pH, concentration of eluent, flow rate of sample and eluent solution, and foreign ions on the sorption of chromium (III) by immobilised ferron column was investigated. Under the optimised conditions the calibration curve was linear over the range of 2–400 µg L for 1000 mL preconcentration volume. The detection limit was 0.32 µg L, the preconcentration factor was 400, and the relative standard deviation (%RSD) was 1.9% (at 10 µg L; n = 7). The method was successfully applied to the determination of chromium species in water samples and total chromium in standard alloys.International Journal of Environmental Analytical Chemistry 11/2011; · 1.32 Impact Factor
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ABSTRACT: A redox speciation and preconcentration study of Cr(III) and Cr(VI) using a flow injection system with dual mini-columns prepared from cross-linked polymers - poly(methacrylic acid) and polyvinylimidazole was developed. Characterization of organic polymers were performed by using FTIR, SEM, TG, C:H:N and BET measurements. The equilibrium data obtained from Cr(III) adsorption on poly(methacrylic acid) and Cr(VI) on polyvinylimidazole were fitted very well to the dual site Langmuir-Freundlich model, suggesting the presence homogeneous and heterogeneous binding site and providing maximum adsorption capacities of 1.42 and 3.24 mg g- 1, respectively. The adsorption kinetics data were described by the pseudo-second-order model for both polymers, thus corroborating to isotherm data. The on-line preconcentration/speciation system was operated by loading 18.0 mL of a solution containing Cr(III) and Cr(VI) at pH 4.0 through the dual mini-columns at a flow rate of 3.0 mL min- 1, where Cr(III) was selectively retained on poly(methacrylic acid), whilst Cr(VI) was retained on polyvinylimidazole . The limits of detection were found to be 0.84 and 1.58 μg L- 1 for Cr(III) and Cr(VI), respectively. The preconcentration factor (PF), consumptive index (CI) and concentration efficiency (CE) were found to be 47.3/8.6, 0.38/2.1 mL and 7.88/1.43 min- 1 for Cr(III) and Cr(VI), respectively. The developed method was successfully applied to the speciation of chromium in different kinds of water samples. Satisfactory recovery values ranging from 89.9 to 108.3% were obtained.Microchemical Journal 11/2014; · 3.58 Impact Factor
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ABSTRACT: Toxic Cr(III) which poses environmental hazard to flora and fauna was efficiently abstracted by low-cost Nauclea diderrichii seed biomass (NDS) with good sequestral capacity for this metal was investigated in this study. The NDS surface analyses showed that it has a specific surface area of 5.36 m 2 /g and pHpzc of 4.90. Thermogravimetric analysis of NDS showed three consecutive weight losses from 50–200°C (ca. 5%), 200–400°C (ca. 35%), >400°C (ca. 10%), corresponding to external water molecules, structural water molecules and heat induced condensation reactions respectively. Differential ther-mogram of NDS presented a large endothermic peak between 20–510°C suggesting bond breakage and dissociation with the ultimate release of small molecules. The experimental data showed kinetically fast biosorption with increased initial Cr(III) concen-trations, indicating the role of external mass transfer mechanism as the rate controlling mechanism in this adsorption process. The Langmuir biosorption capacity of NDS was 483.81 mg/g. The use of the corrected Akaike Information Criterion tool for ranking equilibrium models suggested that the Freundlich model best described the experimental data, which is an indication of the heterogeneous nature of the active sites on the surface of NDS.Journal of Saudi Chemical Society 11/2012; · 1.29 Impact Factor