- Simultaneous determination of Cr(III) and Cr(VI) in tannery wastewater using low pressure ion chromatography combined with flow injection spectrophotometry
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Trivalent and hexavalent chromium have been successfully separated and determined using low pressure ion chromatography combined with flow injection spectrophotometric analysis (LPIC-FIA). A column packed with crosslinking starch microspheres was used for on-line separation of Cr(III) from Cr(VI) in a flow-injection system because of its absorptive effect on Cr(III). To determine the concentration of Cr(III) and Cr(VI) in samples, we used 3.0 mmol/L nitric acid to elute adsorbed Cr(III) from the column and then used ceric sulfate-sulfuric acid as oxidant to convert all Cr(III) into Cr(VI). Then, Cr(VI) directly came from the samples and Cr(VI) came from Cr(III) successively formed a amaranthine complex with diphenycarbazide and the complex shows a maximum absorption at 530 nm. Analytical parameters including the concentration of eluent and oxidant solution, oxidizing temperature, length of oxidizing reaction coil, reaction coil and injection coil, interfering effects, etc., were optimized. The limit of detection was 1.25 μg/L for Cr(VI) and 3.76 μg/L for Cr(III). The linear relationship between absorption with the concentration of Cr(VI) and Cr(III) was 0.001-1.000 mg/L and 0.030-1.000 mg/L with correlation coefficients of 0.9995 and 0.9994, respectively. The relative standard deviation of Cr(VI) and Cr(III) was 1.21% and 1.66%, respectively (n = 10). Major cations and anions did not show any interference. We validated this method through certified reference materials and through measuring the recovery in tannery wastewater.
- Chen, Shujuan,Zhang, Xinshen,Yu, Lingyun,Wang, Li,Li, Hui
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- Modulated Cr(III) oxidation in KOH solutions at a gold electrode: Competition between disproportionation and stepwise electron transfer
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The electrochemical oxidation of aqueous Cr(III) was examined using cyclic voltammetry with a polycrystalline Au electrode in KOH solutions of varying pH and Cr(III) concentration. The mechanism and kinetics for the oxidation of Cr(III) is a quasi-reversible diffusion-controlled reaction and is largely dependent on the solution pH. The reaction mechanism is initiated by an irreversible electrochemical electron transfer to form Cr(IV) which is the rate-determining step (RDS). Following the RDS, subsequent oxidation of Cr to its hexavalent state occurs by the disproportionation of Cr(IV) at low KOH concentrations and electron transfer at high KOH concentrations due to the involvement of OH- in the disproportionation reaction. As the solution pH increases, the Cr(III) oxidation peak potential shifts negatively owing to the involvement of OH- in the RDS. The competitive adsorption of OH- and CrO2- on the electrode surface also plays an important role in the oxidation behavior.
- Jin, Wei,Moats, Michael S.,Zheng, Shili,Du, Hao,Zhang, Yi,Miller, Jan D.
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- Oxidation of chromium (III) by periodate in aqueous alkaline medium - A kinetic study
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The kinetics of oxidation of chromium(III) by periodate in aqueous alkaline medium at 27°C obeys the rate law where K1 is dissociation constant of the equilibrium H3IO62- ? H2IO63-+H+, k1 and k2 are the rate constants for the slow steps of the reactions H2IO63-- Cr(OH)4- and H3IO62-- Cr(OH)4- respectively. The constants k1 and k2 are calculated and used to regenerate the experimental rate constants at various conditions.
- Hiremath,Tuwar,Nandibewoor
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- Kinetics and mechanism of oxidations of [N-(2-hydroxyethyl) emylene-diamine-N,N′,N′-triacetato] chromium (III) by N- bromosuccinimide
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The kinetics of oxidation of [N-(2-hydroxyethyl)ethylenediamine-N,N′-N′-triacetato] chromium (HI) complex [CrIII (H2O)(TOH) by N-bromosuccinimide(NBS) in aqueous solution to yield chromium (IV) has been studied spectrophotometrically at 20-40°C range. The reaction is first order each in [NBS] and [CrIII], and the rate increases with increase in pH between 6.30 and 7.33. The thermodynamic activation parameters have been calculated. The experimental rate law is consistent with a mechanism in which the deprotonated [CrIII(OH)(TOH)-] is considered to be the most reactive species compared to its conjugate acid. It is assumed that electron transfer takes place via an inner-sphere mechanism.
- Abdel-Khalek, Ahmed A.,Sayyah, El-Said M.,Khaled, Eman S.H.
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p. 489 - 492
(2007/10/03)
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- Kinetics and mechanism of silver (I) catalysed oxidation of chromium (III) by peroxidiphosphate in acetate buffers
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In the title reaction the rate is independent of the and occurs by the redox cycle Ag(I)/Ag(II) through four steps: H2P2O82- + Ag+ (k1); H2P2O82- + AgO2CCH3 (k'1); HP2O83- + Ag+ (k2); HP2O83- + AgO2CCH3 (k'2). k1, k'1, k2 and k'2 (dm3mol-1s-1) are 0.017, 0.069, 0.19 and 0.36, respectively at 40 deg and ionic strength = 1.0 mol dm-3.
- Parashar, Pradeep,Sharma, P. D.,Gupta, Y. K.
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p. 383 - 386
(2007/10/02)
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- Kinetics of the Oxidation of chromium(III) by Periodate
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The kinetics of oxidation of III(H2O)(TOH)>, (TOH=N-(2-hydroxyethyl)ethylenediamine-N,N',N'-triacetate) by periodate in aqueous solutions has been found to obey the following equation: where k2 is the rate constant for
- Abdel-Khalek, Ahmed A.,Elsemongy, Mahmoud M.
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p. 4407 - 4410
(2007/10/02)
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