The Separation and Determination of Chromium(VI) by Reducing Elution Using Anion Exchange Resin and Sodium Sulfite

International Journal of Environmental Analytical Chemistry

2006

A XAD-shellac sorbent, synthesized by the impregnation of the natural polymer shellac (purified product of the hardened resinous secretion of the lac insect Kerria lacca) on Amberlite XAD-16 copolymer backbone, has been developed for the separation of Cr(III) from Cr(VI), and preconcentration of Cr(III) from synthetic solutions and real samples. The preconcentration factor for Cr(III) was 75. All chromium determinations were made using the diphenyl carbazide spectrophotometric method after oxidizing Cr to chromate(VI) where necessary, and simultaneously with flame-AAS for confirmation. The dynamic breakthrough and batch capacities of this sorbent for Cr(III) were 0.3 and 0.9 mg g À1 , respectively, indicating that the ion-exchange mechanism was prevalent in the dynamic mode, whereas in the batch mode, the surface sites were also capable of exerting their chelating effects. When XAD-shellac was thoroughly washed with ammonium acetate solution prior to use in chromium speciation, the cationic (RH þ ) surface sites were probably neutralized to yield free acetic acid, and the resulting resin did not retain CrO 2À 4 : Thus, complete separation and speciation of Cr(III) from CrO 2À 4 was possible using this sorbent. The shellac-coated sorbent decomposed in alkaline solution (i.e. over pH 7.5), and therefore the retained Cr(III) was eluted with dilute (0.025-0.050 M) HCl. Thus, Cr(III) in admixture with Cr(VI) could be separated and recovered, without interference from the hexavalent state. XAD-shellac was not successful for Cr preconcentration from seawater, but was efficiently used for synthetic and real electroplating wastewater and CRMs such as SO-2 soil, San Joaquin soil, BCR 145 R sewage sludge, with a recovery ratio for Cr(III)/Cr(VI) extending up to 98%.

Section: Introductionmentioning

confidence: 99%

Chromium speciation analysis by separation of Cr(III) from Cr(VI) on a XAD sorbent derivatized with shellac: a natural polymer

Yalçın

International Journal of Environmental Analytical Chemistry

2006

“…On the other hand, Cr(III) may be retained selectively using sorbent containing polyaminophosphonic acid [6], immobilized quinoline-8-ol or iminodiacetate functional groups [7], and quinoline-8-ol complexed macroporous resin [8]. For Cr(III)-specific ion exchangers, Cr(VI) in solution may be reduced to Cr(III) with acidic solutions of ascorbic acid [9], NH 2 OH.HCl [10], ammonium ferrous sulfate [11], or Na 2 SO 3 so as to measure total chromium [12]. Thus the same sorbent column can be used to concentrate both valences of chromium, rendering speciation analysis possible.…”

Section: Introductionmentioning

confidence: 99%

Speciation analysis of chromium by separation on a 5-palmitoyl oxine-functionalized XAD-2 resin and spectrophotometric determination with diphenylcarbazide

Filik

Doğutan

Analytical and Bioanalytical Chemistry

2003

The method developed in this work for the separation and preconcentration of Cr(III) is based on its retention by an Amberlite XAD-2 copolymer resin functionalized with 5-palmitoyl-8-hydroxyquinoline (oxine), abbreviated XAD-POx, with the ligand covalently bound to the copolymer. Cr(III) sorption was quantitative within the pH range 4.5-7.0 and Cr(VI) was not retained. The Cr(III) held by the resin column was eluted with a hot solution of H(2)O(2) in pH>or=9.0 aqueous NH(3)-NH(4)Cl buffer, and Cr oxidized to CrO(4)(2-) was rejected by the chelating cation-exchanger column. Any Cr(VI) originally present with Cr(III) could be reduced with an acidic solution of H(2)O(2), and retained by the column yielding total Cr results, Cr(VI) being determined from the difference. The resin showed a maximal preconcentration factor of 60 for Cr(III), the LOD and LOQ being 9.3 and 30.1 nmol L(-1), respectively. The developed preconcentration-speciation analysis was finished with a diphenylcarbazide (DPC) spectrophotometric procedure suitable for conventional laboratories. The resin showed excellent salt tolerance, enabling Cr analysis in seawater, and was stable over extended use. All the interferents of this procedure that normally occur in an electroplating effluent, a blended coal CRM, and a standard steel sample could be removed by the recommended procedure, by use of partial and total selectivity at the adsorption and desorption stages, respectively, enabling preconcentration and colorimetric determination of chromium in various complex matrices.

“…For performing the reductive elution of Cr(VI), var-ORDER REPRINTS ious reductant solutions, such as 9% ascorbic acid in 1 M HCl (16), hydroxylamine in 1 M H 2 SO 4 (17), ammonium ferrous sulfate in 1 M HCl (18), 10% NH 2 OH и HCl (19), 5% Na 2 SO 3 in 0.1 M HCl (20), and 0.01M Na 2 SO 3 in 0.1 M H 2 S0 4 (21), were used.…”

Section: Introductionmentioning

confidence: 99%

Recovery of Copper (Ii) and Chromium (Iii,vi) From Electroplating-Industry Wastewater by Ion Exchange

Yalçın

Separation Science and Technology

Hızal

et al. 2001

Two laboratory-scale separation processes have been developed for the recovery of copper (II) from acidic and cyanide-containing alkaline wastewater of electroplating industries. Acidic bath wastes were treated with Dowex 50X8, a strongly acidic cation-exchange resin, and the retained copper was eluted with H 2 SO 4 . The cyanide-containing alkaline bath waste was first oxidized with excessive hypochlorite, then neutralized, and recovered by the use of Amberlite IRC-718 chelating resin. Copper was eluted with H 2 SO 4 .The two different valencies of chromium have been recovered from electroplating-industry wastewater by different separation processes: The predominant valency, Cr(VI), was retained on a strongly basic Dowex 1X8 resin and eluted with a NaCl and ORDER REPRINTS NaOH solution. Alternatively, Cr(III), either existing originally in electroplating-industry waste-rinse mixtures or converted from Cr(VI) by reduction with Na 2 SO 3 , could be recovered by a weakly acidic Amberlite IRC-50 resin and eluted with a solution containing H 2 O 2 and NaOH. Where plating industry wastes contain high levels of organic contamination, Cr(VI) would be naturally reduced to Cr(III) upon acidification, and it may be more economical to recover all chromium as Cr(III).