アルカリ溶液中のクロム（III）とクロム（VI）の分別定量のためのイオン交換樹脂の比較

抄録

The retention behavior of Cr(III) and Cr(VI) in an alkaline solution (0.28 M Na₂CO₃/0.5 M NaOH, pH 13.5 ; US EPA Method 3060A) on four kinds of ion-exchange resins was examined. Method 3060A is an alkaline digestion procedure for extracting Cr(VI) in soils, sludges, sediments, and similar waste materials. Two commercially available ion-exchange resins were used in column operation : Dowex 50W-X8 (H⁺ form and Na⁺ form) and Dowex 1-X8 (OH⁻ form and Cl⁻ form). Column operation was made by pipetting a 15-mL aliquot of an original alkaline solution or a 10-fold diluted alkaline solution, spiked with Cr(III) and/or Cr(VI) to give 1 mg/mL, through a mini-column containing 2.0 g of ion-exchange resin. To compare the observed data, acidic solutions containing Cr(III) and/or Cr(VI) were also loaded. Then, the 1-mL fractions of the effluent were collected in small test tubes for both pH and flame AAS measurements, and break-through curves were illustrated and analyzed. It was found that both Cr(III) and Cr(VI) were not retained on the Na⁺ form cation-exchange column using both alkaline solutions. However, a selective separation of Cr(VI) from Cr(III) could be achieved by retaining Cr(III) on the H⁺ form cation-exchange column using a 10-fold diluted alkaline solution. Therefore, the separated Cr(VI) can be determined by a direct AAS measurement of the resulting effluent. On the OH⁻ form and the Cl⁻ form anion-exchange columns, both Cr(III) and Cr(VI) were retained using a 10-fold diluted alkaline solution. However, a selective separation of Cr(III) from Cr(VI) could be achieved by retaining Cr(VI) on the OH⁻ form and the Cl⁻ form anion-exchange columns using an original alkaline solution. Therefore, the separated Cr(III) could be determined by a direct AAS measurement of the resulting effluent.