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 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.     

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.     

Complexes of chromium(III) with 2,3-dihydroxynaphthalene-6-sulfonic acid and 4,5-dihydroxynaphthalene-2,7-disulfonic acid in aqueous solution

The chromium(III) complex species formed, in acidic and basic solutions at 25.0+/-0.1 degrees C, between Cr(III) and 2,3-dihydroxynaphthalene-6-sulfonic acid (2,3-DHN-6-SA, H(2)L(2-)) and 4,5-dihydroxynaphthalene-2,7-disulfonic acid (4,5-DHN-2,7-DSA, H(2)L(-)) were determined. Over the acidic pH range, the coordination of 2,3-DHN-6-SA and 4,5-DHN-2,7-DSA to Cr(III) in 1 : 1 mole ratio occurs, and CrL and CrL(-) type complexes are formed. At near neutral pH, CrL(OH)(-) and CrL(OH)(2-) type hydroxo complexes are formed. The acid-dissociation constants of ligands and the formation constants of chromium(III) complexes were determined in 0.1 m KNO(3) ionic medium by potentiometric titration using the BEST computer program. Thus, the removing capacities of these ligands could be examined by calculating the equilibrium concentration of Cr(III) that exists in the discharge water of various industries since Cr(III) ions are the main pollutants present during waste water treatment in our city, Bursa.     

Removal of hexavalent chromium from wastewaters by bone charcoal

The adsorption of hexavalent chromium onto bone charcoal was studied as a function of time, amount of charcoal, pH, concentration of chromium and sample volume. The cross interference with other elements was also investigated. Tests were carried out with solutions of chromium(VI) at concentrations between 5 and 25 mg · L^–1. Chromium removal efficiencies higher than 90% were achieved at pH = 1 using 2 g of bone charcoal and a stirring time in the order of 30 min. Acid and alkaline pretreatments of bone charcoal did not improve the sorption capacity of bone charcoal against Cr(VI). The presence of other ions had practically no influence on the chromium removal. The presence of a matrix of tannery effluents did not reduce the removal capacity of bone charcoal for Cr(VI), but it was confirmed that only 47% of Cr(III) can be removed using these conditions. Received: 20 July 1998 / Revised: 4 October 1998 / Accepted: 10 October 1998     

Speciation of chromium by in-capillary reaction and capillary electrophoresis with chemiluminescence detection

A sensitive method for the simultaneous determination of chromium(III) (Cr3+) and chromium(VI) (CrO4(2-)) using in-capillary reaction, capillary electrophoresis (CE) separation and chemiluminescence (CL) detection was developed. The chemiluminescence reaction was based on luminol oxidation by hydrogen peroxide in basic aqueous solution catalyzed by Cr3+ ion followed by capillary electrophoresis separation. Based on in-capillary reduction, chromium(VI) can be reduced by acidic sodium hydrogensulfite to form chromium(III) while the sample is running through the capillary. Before the electrophoresis procedure, the sample (Cr3+ and CrO4(2-)), buffer and acidic sodium hydrogensulfite solution segments were injected in that order into the capillary, followed by application of an appropriate running voltage between both ends. As both chromium species have opposite charges, Cr3+ ions migrate to the cathode, while CrO4(2-) ions, moving in the opposite direction toward the anode, react with acidic sodium hydrogensulfite which results in the formation of Cr3+ ions. Because of the migration time difference of both Cr3+ ions, Cr(III) and Cr(VI) could be separated. The running buffer was composed of 0.02 mol l(-1) acetate buffer (pH 4.7) with 1 x 10(-3) mol l(-1) EDTA. Parameters affecting CE-CL separation and detection, such as reductant (sodium hydrogensulfite) concentration, mixing mode of the analytes with CL reagent, CL reaction reagent pH and concentration, were optimized. The limits of detection (LODs) of Cr(III) and Cr(VI) were 6 x 10(-13) and 8 x 10(-12) mol l(-1) (S/N=3), respectively. The mass LODs for Cr(III) and Cr(VI) were 1.2 x 10(-20) mol (12 zmol) and 3.8 x 10(-19) mol (380 zmol), respectively.     

Preconcentration of trace metals on Amberlite XAD-4 resin coated with dithiocarbamates and determination by inductively coupled plasma-atomic emission spectrometry in saline matrices

Preconcentration of Cd(II), Cu(II), Mn(II), Ni(II), Pb(II) and Zn(II) in saline matrices on Amberlite XAD-4 resins coated with ammonium pyrrolidine dithiocarbamate (APDC) and piperidine dithiocarbamate (pipDTC) and subsequent determination by inductively coupled plasma atomic emission spectrometry were studied. Parameters such as effect of pH, effect of HNO(3) concentration on elution of metals from resin were studied. The results show that Amberlite XAD-4 coated with APDC was more efficient in the recovery of metal ions compared with Amberlite XAD-4 coated with pipDTC, in the concentration range of 0.1-200 mug l(-1), for 1 g of Amberlite XAD-4 coated resin. The detection limits for Cd(II), Cu(II), Mn(II), Ni(II), Pb(II), Zn(II) are 0.1, 0.4, 0.3, 0.4, 0.6, 0.5 mug l(-1), respectively, for resin coated with APDC and 0.7, 1.0, 0.8, 0.9, 1.7 and 1.2 mug l(-1) for resin coated with pipDTC. The effect of diverse ions on the determination of aforesaid metals was studied. The method was applied for the determination of trace metal ions in artificial sea water and natural water samples. The results were compared with extraction AAS method.     

Spectrophotometric determination of trace amounts of cobalt with 2-hydroxybenzaldehyde-5-nitro-pyridylhydrazone in presence of surfactant after separation with Amberlite IRC-718 resin

2-Hydroxybenzaldehyde-5-nitro-pyridylhydrazone (2HB-5NPH) was synthesized and its application in the spectrophotometric determination of metal ions was studied in the presence of surfactants. A separation procedure, using a short column filled with Amberlite IRC 718, is proposed for the spectrophotometric determination of traces of cobalt. The influence of several ions, as interference, was discussed. The procedure was applied to determination of cobalt in mixture sample with satisfactory results (≥recovery 96%; relative error ≤2%; relative standard deviation ≤1.2% in the concentration range of 0.02–2.0 mg l⁻¹; detection limit, 0.01 mg l⁻¹ in solution). Control of the pH during the column operation is essential because the adsorption capacities are very sensitive to change in pH. Their separation was carried out in 0.005 M Malic acid, 1.5 M HCl, 2.0 M HNO₃ media.     

Synthesis and characterization of a new resin functionalized with 2-naphthol-3,6-disulfonic acid and its application for the speciation of chromium in natural water

A polystyrene divinyl benzene (8%) copolymer has been functionalized by coupling it through NN group with 2-naphthol-3,6-disulfonic acid (NDSA). The resulting resin has been characterized by elemental analysis, thermogravimetric analysis and infrared spectra. The hydrogen ion, water regain and metal ion capacities of the resin have been determined. Two forms of chromium show different exchange capacities at different pH values, viz. Cr(III) selectively retained at pH 6.5 whereas Cr(VI) retained at pH 1.5. Hence complete separation of the two forms of chromium is possible. The kinetic studies show that the exchange of Cr(III) and Cr(VI) follows second-order kinetics. The metal ion concentration was measured by flame atomic absorption spectrometry. The method has been successfully applied for the speciation of chromium in natural water samples.     

The spectrophotometric determination of chromium in sea water

The coprecipitation of chromium from sea water by several precipitates was examined. With hydrous iron(III) oxide a recovery of chromium of >99% was obtained within the pH range 7.0–9.0 at a chromium level of ca. 0.4 μg/l. Chromium was separated from iron by anion exchange and determined spectrophotometrically using diphenylcarbazide. The method showed a precision of ±0.02 μg Cr/1. Chromium occurs in sea water in the 3+ oxidation state.     

Preconcentration of total chromium on Dowex 50W-X8 resin loaded with 2-amino-benzenethiol

Application of Dowex 50W-X8 loaded with 2-amino-benzenethiol for preconcentration of total chromium (Cr(VI) and Cr(III)) in water samples and subsequent determination by inductively coupled plasma-atomic emission spectrometry was studied. The reagent 2-amino-benzenethiol loaded onto the resin effectively reduced Cr(VI) to Cr(III) and total chromium (both Cr(VI) and Cr(III)) formed chelate complex with the reagent in the Cr(III) valence state. Experimental parameters such as preconcentration time, solution flow rates, pH, and concentration of the eluent were optimized. The method has been applied for the determination of total chromium in seawater samples in the range of 0.1–200?µg?L^?1. A detection limit of 0.3?µg?L^?1 was achieved, and the relative standard deviation was about 5%.     

Malachite green as a reagent for detection and spectrophotometric determination of chromium(VI)

A sensitive and inexpensive method of spectrophotometric determination of chromium(VI), based on the absorbance of its complex with malachite green and acetic acid at pH 2.5 is reported. The complex shows a molar absorptivity of 8 x 10(4) l.mole(-1) cm(-1) at 560 nm, using malachite green and acetic acid as reference solution. The effect of time, temperature, pH and reagent concentration is studied and optimum operating conditions are established. Beer's law is applicable in the concentration range 2.0-22.8 mug/ml chromium(VI). The resin beads act as a catalyst and as little as 1.6 mug of chromium(VI) is detected in the resin phase as compared to 4.1 mug in the solution phase. The standard deviation in the determinations is +/-0.40 mug/ml for a 10.35 mug/ml solution.     

Determination of chromium(III) and total chromium in water by derivative atomic absorption spectrometry using flow injection on-line preconcentration with a double microcolumn.

A rapid and sensitive method has been proposed for the sequential determination of chromium(III) and total chromium in water samples by flame atomic absorption spectrometry combined with a flow injection on-line preconcentration on a double-microcolumn. The chromium(III) and total chromium in samples were retained on a double-microcolumn with a cation exchange resin, respectively, and eluted directly into a nebulizer by 3 mol L(-1) HNO3. The characteristic concentration (gives a derivative absorbance of 0.0044) and the detection limit (3sigma) for chromium were 0.512 microg L(-1) and 0.647 microg L(-1) for a preconcentration time of 1 min, respectively. This is an improvement of 20 and 14-times than those of conventional FI-FAAS. The proposed method allows the determination of chromium in the range of 0-90 microg L(-1) with a relative standard deviation of 3.63% at the 10 microg L(-1) level. The method has been applied for the analysis of chromium in reference water of National Research Center for Certified Reference Materials (GBW08607) and other water samples with satisfactory results.     

Speciation studies by capillary electrophoresis- Simultaneous determination of chromium(III) and chromium(VI)

A method for the simultaneous determination of chromium(III) and chromium(VI) by capillary electrophoresis (CE) has been developed. The chromium(III) has been chelated with 1,2-cyclohexanediaminetetraacetic acid (CDTA) in order to impart a negative charge and similar mobility to both the chromium(III) and the chromium(VI) species. The effects of the amount of the reagent, pH and heating time required to complete the complexation have been studied. Factors affecting the CE behaviour such as the polarity of electrodes and the pH of electrophoretic buffer have been investigated. The separated species have been monitored by direct UV measurements at 214 nm. The detection limits achieved are 10 microg/l for Cr(VI) and 5 microg/l for Cr(III) and linear detector response is observed up to 100 mg/l. The procedure has been applied to the determination of both chromium species in industrial electroplating samples and its accuracy was checked by comparing the results (as total chromium) with those of atomic absorption spectrometry. No interference occurred from transition metal impurities under optimized separation conditions. The method is also shown to be feasible for determining Cr(III) as well as other metal ions capable to form complexes with CDTA (like iron(III), copper(II), zinc(II) and manganese(II)) in pharmaceutical preparations of essential trace elements.     

Non-destructive radioanalytical technique in characterization of anion exchangers Amberlite IRN78 and Indion H-IP

The present study deals with characterization of industrial grade anion exchange resins Amberlite IRN78 and Indion H-IP for which non-destructive radiotracer technique using ¹³¹I and ⁸²Br was used. The radioisotopes were used to trace the kinetics of iodide and bromide ion-isotopic exchange reactions taking place in the two resins. It was observed that under identical experimental conditions of 40.0 °C, 1.000 g of ion exchange resins and 0.003 M labeled iodide ion solution for iodide ion-isotopic exchange reaction, the values of specific reaction rate (min^?1), amount of iodide ion exchanged (mmol), initial rate of iodide ion exchange (mmol min^?1) and log K _d were 0.285, 0.544, 0.155 and 12.6 respectively for Amberlite IRN78 resin, which was higher than 0.093, 0.315, 0.029 and 4.9 respectively as that obtained by using Indion H-IP resins. Also at a constant temperature of 40.0 °C, as the concentration of labeled iodide ion solution increases 0.001–0.004 M, the percentage of iodide ions exchanged increases from 68.10 to 74.00 % for Amberlite IRN78 resin, which was higher than the increase of 40.20–42.80 % as observed for Indion H-IP resins. The identical trend was observed for the two resins during bromide ion-isotopic exchange reaction. The overall results indicate that that under identical experimental conditions Amberlite IRN78 resins shows superior performance over Indion H-IP resins.     

Development of a procedure for studies of the chromium(III) and chromium(VI) contents of welding fumes

A method for speciation studies of chromium in welding fumes is described. Separation of chromium(III) and chromium(VI) in aqueous extracts of welding fumes is obtained by using anion- and cation-exchange resins. Atomic absorption spectrometry is used for quantification. At pH 3–5, there is no loss of chromium(III) as the hydroxide nor reduction of chromium(VI) by iron(II). Two types of welding fumes were studied: for ESAB OK 67–52 and AROSTA 316 L fumes, 57 and 91%, respectively, of the total chromium content was water-soluble; the total chromium contents were 5.9 and 4.4%, respectively. Chromium(III) was not detected in the aqueous extracts of either type of fumes (< 0.010 μg ml^-1 of extract).     

Protonation and ion exchange equilibria of weak base anion-exchange resins

Protonation and ion exchange equilibria of weak base anion-exchange resins, in which tertiary amine moieties were introduced as a functional group, were investigated by applying NMR spectroscopy to species adsorbed into the resins. ³¹P NMR signals of the phosphinate ion in the resin phases shifted to a lower field due to the influence of protonation of the tertiary amine groups of the resins in the pH range of 4-10. Protonation constants of the tertiary amine groups in styrene-divinylbenzene (DVB)-based resins were estimated to be K_H = 10^6.4 for Amberlite IRA96 and 10^6.5 for DIAION WA30 by the ³¹P NMR method using the phosphinate ion as a probe species. In addition to the low field shift caused by the protonation of the tertiary amine moieties, another low field shift was observed for the phosphinate ion in acrylic acid-DVB-based resins at a rather high pH. This shift should be due to an unexpected deprotonation in the acrylic resin: a tautomerism accompanying the proton release from the amide form to the imide one in the functional group, thus, the resin could exhibit a cation exchange property at the high pH. Protonation constants of the tertiary amine moieties in the acrylic resins were estimated to be 10^8.8 for DIAION WA10, 10^9.0 for Amberlite IRA67 and 10^9.3 for Bio-Rad AG 4-X4 on the basis of the Henderson-Hasselbalch equation using the resin phase pH estimated by the ¹³³Cs and ¹H NMR signal intensities.     

Separation,preconcentration and speciation of chromium by solid phase extraction on immobilised ferron

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^?1 for 1000?mL preconcentration volume. The detection limit was 0.32?µg?L^?1, the preconcentration factor was 400, and the relative standard deviation (%RSD) was 1.9% (at 10?µg?L^?1; n?=?7). The method was successfully applied to the determination of chromium species in water samples and total chromium in standard alloys.     

Speciation of chromium in wastewater and sludge by extraction with liquid anion exchanger Amberlite LA-2 and electrothermal atomic absorption spectrometry

A simple, integrated method for the speciation of chromium in wastewater and sewage sludge was developed, utilising liquid anion exchange by Amberlite LA-2 (LAES) and final determination by electrothermal atomic absorption spectrometry (ETAAS). Samples were filtered through a 0.45 μm membrane filter and chromium species were determined in filtered water samples and in sludge on the filters. In the former case (filtrate), total Cr was determined directly by ETAAS, while for the determination of Cr(VI) the filtrate was buffered to pH 6.4, extracted with LAES and Cr(VI) was determined in the organic extract. Cr(III) was determined by the difference. In the latter case (filter), the filters were leached with an alkaline buffer solution (pH 12.7) and the supernatant was subjected to the same extraction procedure. For the determination of total leachable Cr, the filters were subjected to acid leaching with dilute HNO₃ (pH 1) and the supernatant was subjected to ETAAS, after appropriate dilution with water. Then, Cr(III) was determined by the difference. The limits of detection (LOD) were 0.39 and 0.45 μg l⁻¹ for total Cr and Cr(VI), respectively, in the dissolved phase and 2.10 and 0.87 ng g⁻¹ for total Cr and Cr(VI) in the suspended solids. The recoveries of total Cr and Cr(VI) in filtrated wastewater samples and filters were quantitative, ranged from 93 to 106%. The effect of time and temperature of sonication and suspended solids concentration on total Cr and Cr(VI) recovery was studied. No significant difference in recoveries was obtained for sonication temperatures between 30 and 70 °C. However, sonication time equal to or higher than 30 min and concentration of suspended solids equal to or less than 30 mg significantly improved Cr recovery. The ETAAS program for the determination of Cr(VI) in Amberlite/MIBK extract was carefully optimised in the absence of a chemical modifier to avoid memory effects. The developed analytical method was applied for the determination of chromium species in wastewater and suspended solids of a municipal and a lab-scale wastewater treatment plant.     

Azocalix[4]pyrrole Amberlite XAD-2: New polymeric chelating resins for the extraction, preconcentration and sequential separation of Cu(II), Zn(II) and Cd(II) in natural water samples

Two novel azocalix[4]pyrrole Amberlite XAD-2 polymeric chelating resins were synthesized by covalently linking diazotized Amberlite XAD-2 with calix[4]pyrrole macrocycles. The chelating resins were used for extraction, preconcentration and sequential separation of metal ions such as Cu(II), Zn(II) and Cd(II) by column chromatography prior to their determination by UV/vis spectrophotometry or flame atomic absorption spectrophotometry (FAAS) or inductively coupled plasma atomic emission spectroscopy (ICP-AES). Various parameters such as effect of pH on absorption, concentration of eluting agents, flow rate, total sorption capacity, exchange kinetics, preconcentration factor, distribution coefficient, breakthrough capacity and resin stability, were optimized for effective separation and preconcentration. The resin showed good ability for the separation of metal ions from binary and ternary mixture on the basis of pH of absorption and concentration of eluting agents. The newly synthesized resins showed good potential for trace enrichment of Cu(II), Zn(II) and Cd(II) metal ions, especially for Cu(II), as compared to the earlier reported resins. The synthesized resins were recycled at least 8-10 times without much affecting column sorption capacity. The presented method was successfully applied for determination of Cu(II), Zn(II) and Cd(II) in natural and ground water samples.