Adsorption behavior of chromium(III,VI) on activated carbon and oxine-impregnated activated carbon.
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The adsorption behavior of chromium(III, VI) onto activated carbon (AC, Merck Co. Ltd.) and oxine-impregnated activated carbon (AC(HOx)) was investigated by use of a column method. The adsorption of chromium(III, VI) onto activated carbon, and of chromium(VI) onto AC(HOx) showed remarkable pH-dependency. The optimum pH for the adsorption of chromium(VI) from 1.00 × 10-3 mol dm-3 chromium(VI) solution were about 2.5 for activated carbon and about 3.0 for AC(HOx). The amount of chromium(VI) adsorbed onto adsorbents at the optimum pH was 13.5 mg for 5.0 g of activated carbon and 22.0 mg for 5.0 g of activated carbon impregnated with 0.5 g of oxine. Chromium (VI) adsorbed onto activated carbon at pH 4.9 was completely desorbed with 0.10 mol dm-3 NaOH solution in the form of chromium(III) (33%) and chromium(VI) (67%). While less than 6% of the total chromium(VI) adsorbed onto AC(HOx) at pH 4.9 was desorbed with 0.10 mol dm-3 NaOH solution. It seems probable that the chromium(VI) which was adsorbed onto activated carbon in the forms of Cr(OH)(H2O)52+ appeared from the reduction of some portion of chromium(VI) with activated carbon, HCrO4- and Cr2O7-2. On the other hand, chromium(VI) may be adsorbed onto AC(HOx) mainly in the form of Cr(III)-oxine complex.Keywords:
Carbon fibers
Determination of chromium(VI)and chromium(III)in river water by flame atomic absorption spectrometry
Chromium(Ⅵ)can react with diphenylcarbazide(DPC)in perchloric acidic medium to form the complex of chromium(Ⅵ)-DPC which can be extracted with n-pentanol.This was used for the determination of trace chromium(Ⅵ)and chromium(Ⅲ)in river water by flame atomic absorption spectrometry.KMnO_4 was used as the oxidant for the oxidation of chromium(Ⅲ)to chromium(Ⅵ)which was then determined by the same way.The limit of detection was 0.0007 mg·L~(-1)and Beer's law was obeyed in a wide linear dynamic range of 0.0007～1.0 mg·L~(-1)chromium(Ⅵ).The recovery of chromium(Ⅵ)and chromium(Ⅲ)was 100%～112%and 89%～104%,respectively.
Chromate conversion coating
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Specific determination of chromium(III) and chromium(VI) in natural water samples was performed without mutual separation. The chromium in sample solution was concentrated on cation-exchange resin packed in a flow-through cell as a reaction product of chromium(VI) with diphenylcarbazide. The absorbance increase caused by the accumulation of the complex on cation-exchange resin was continuously measured. By using peroxodisulfate as an oxidizing agent, the chromium(III) in sample solution was completely oxidized to chromium(VI). The chromium(III) concentration was calculated by the difference between the values of the total chromium and chromium(VI). The detection limit for chromium(VI) and total chromium was 70 pg and 120 pg, respectively. This method was applied to the specific determination of chromium in several natural water samples. The results of the total chromium obtained by the proposed method show moderate agreement with that obtained with ICP-MS. Unlike the previous results reported in chromium speciation studies, the predominant chromium species in natural water was chromium(VI).
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Absorbance
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Chromium Compounds
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Abstract Trace amount of chromium was first converted quantitatively to volatile chromium chelates such as chromium(III) acetylacetonate, Cr(acac) 1 , chromium(III) trifluoracetylacetonate, Cr(tfa) 3 , and chromium(III) hexafluoroacetylacetonate, Cr(hfa) 3 , and the chelate solution was then analyzed by gas chromatography. It was found that Cr(tfa) 3 is the most suitable chemical form for this purpose. The method was profitably applied to the determination of chromium(III) incorporated in the six kinds of commerical products of potassium Chromate.
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Biosorption
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Three simple, rapid and accurate spectrophotometric procedures are described for the individual determination of chromium(III) and chromium(VI) and the sequential determination of chromium(III) and chromium(VI) in mixtures. The first two procedures are based on measuring the absorbance (ε= 2.64 × 104 at 580 nm) of the coloured product as formed by the reaction between chromium(III or VI) and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP); these two procedures are suitable for the individual determination of chromium(III) or chromium(VI), respectively, in amounts up to about 50 µg per 50 ml when either of them is present in the sample without prior conversion of the valence state of the chromium by additional oxidation or reduction. The third procedure, for the sequential analysis of chromium(VI) and chromium(III), involves the determination of the total amount of chromium with 5-Br-PADAP after the determination of chromium(VI) with diphenylcarbazide [without interference from chromium(III)] and destruction (by boiling) of the excess of diphenylcarbazide and the chromium(III)-diphenylcarbazone complex.The procedures have been applied to the determination of chromium(VI) and chromium(III) in three water samples containing both chromium(III) and chromium(VI) without the need for any additional separation process, masking or solving of simultaneous equations.
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In this paper, corn stalk adsorbents are prepared by pretreated corn stalks and carboxymethylation reaction. Then the adsorbents are used to remove Pb2+ in the aqueous solution, and the effect of the pH value of the solution, adsorption time, adsorbent dosage, the initial concentration of Pb2+ on the adsorption performance, and the adsorption kinetics and adsorption isotherm are discussed. The results show that when the pH is 4.50, the adsorption time is 150 min, the amount of adsorbent is 0.45 g, the adsorption capacity of the adsorbent is as high as 928 mg/g, and the Pb2+ removal rate reaches 99.78 %. The adsorption kinetics showed that the adsorption of Pb2+ by the adsorbent reached adsorption equilibrium within 150 minutes, the adsorption process conformed to the quasi-second-order kinetic model, and the adsorption mechanism was chemical adsorption. The adsorption isotherm shows that the adsorption process of Pb2+ by the adsorbent conforms to the single-layer adsorption of the Langmuir model.
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The adsorption behavior of chromium(III, VI) onto activated carbon (AC, Merck Co. Ltd.) and oxine-impregnated activated carbon (AC(HOx)) was investigated by use of a column method. The adsorption of chromium(III, VI) onto activated carbon, and of chromium(VI) onto AC(HOx) showed remarkable pH-dependency. The optimum pH for the adsorption of chromium(VI) from 1.00 × 10-3 mol dm-3 chromium(VI) solution were about 2.5 for activated carbon and about 3.0 for AC(HOx). The amount of chromium(VI) adsorbed onto adsorbents at the optimum pH was 13.5 mg for 5.0 g of activated carbon and 22.0 mg for 5.0 g of activated carbon impregnated with 0.5 g of oxine. Chromium (VI) adsorbed onto activated carbon at pH 4.9 was completely desorbed with 0.10 mol dm-3 NaOH solution in the form of chromium(III) (33%) and chromium(VI) (67%). While less than 6% of the total chromium(VI) adsorbed onto AC(HOx) at pH 4.9 was desorbed with 0.10 mol dm-3 NaOH solution. It seems probable that the chromium(VI) which was adsorbed onto activated carbon in the forms of Cr(OH)(H2O)52+ appeared from the reduction of some portion of chromium(VI) with activated carbon, HCrO4- and Cr2O7-2. On the other hand, chromium(VI) may be adsorbed onto AC(HOx) mainly in the form of Cr(III)-oxine complex.
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