Separation and enrichment of Cr(VI) ion in waters using solid phase extraction and evaluation of adsorption, kinetic and thermodynamic parameters

Cr(III) and Cr(VI) ions in waters were separated by using column method containing Amberlite IRA 900 copolymer resin. Cr(VI) ion was separated, pre-concentrated and determined by using flame atomic absorption spectrometry. After oxidizing all Cr(III) into Cr(VI) with H2O2, whole chromium (Cr(III) + Cr(VI) ions) was determined. Concentration of Cr(III) was obtained by subtracting Cr(VI) level from whole chromium. Recovery of Cr(VI) ion at optimum conditions such as pH (5.5 – 6), type and concentration of eluent solution (5 mL of 1 mol/L HCl + 2% (m/v) ascorbic acid) and flow rate (3 mL/min) obtained was 99 ± 1% for five replicate measurements. Analytical detection and quantification limits were found as 0.11 and 0.38 µg/L, respectively. The enrichment factor of Cr(VI) ion found was about 100 after using optimization conditions. Accuracy of proposed method was checked by analyzing Cr(VI) in CWW-TM-D Wastewater (SRM) containing Cr(III) and Cr(VI) ions and applied to real waters. Langmuir adsorption model was suitable for Cr(VI) ion and maximum adsorption capacity found was 303 mg/g at 298 K. Thermodynamic parameters (ΔG°, ΔH° and ΔS°) and activation energy (Ea) were determined. Adsorption of Cr(VI) ion on resin was chemical ion-exchange, spontaneous and exothermic process.