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ABSTRACT
The aim of this study was to investigate Cr(VI) removal from chromium-plating rinse water using modacrylic anion-exchange fibers (KaracaronTM KC31). Batch experiments were performed with synthetic Cr(VI) solutions to characterize the KC31 fibers in Cr(VI) removal. Cr(VI) removal by the fibers was affected by solution pH; the Cr(VI) removal capacity was the highest at pH 2 and decreased gradually with a pH increase from 2 to 12. In regeneration and reuse experiments, the Cr(VI) removal capacity remained above 37.0 mg g−1 over five adsorption–desorption cycles, demonstrating that the fibers could be successfully regenerated with NaCl solution and reused. The maximum Cr(VI) removal capacity was determined to be 250.3 mg g−1 from the Langmuir model. In Fourier-transform infrared spectra, a Cr = O peak newly appeared at 897 cm−1 after Cr(VI) removal, whereas a Cr–O peak was detected at 772 cm−1 due to the association of Cr(VI) ions with ion-exchange sites. X-ray photoelectron spectroscopy analyses demonstrated that Cr(VI) was partially reduced to Cr(III) after the ion exchange on the surfaces of the fibers. Batch experiments with chromium-plating rinse water (Cr(VI) concentration = 1178.8 mg L−1) showed that the fibers had a Cr(VI) removal capacity of 28.1–186.4 mg g−1 under the given conditions (fiber dose = 1–10 g L−1). Column experiments (column length = 10 cm, inner diameter = 2.5 cm) were conducted to examine Cr(VI) removal from chromium-plating rinse water by the fibers under flow-through column conditions. The Cr(VI) removal capacities for the fibers at flow rates of 0.5 and 1.0 mL min−1 were 214.8 and 171.5 mg g−1, respectively. This study demonstrates that KC31 fibers are effective in the removal of Cr(VI) ions from chromium-plating rinse water.
Funding
This research was supported by the Korea Ministry of Environment as the Advanced Technology Program for Environmental Industry (Grant no. 2016000140011).
Nomenclature
| a | = | modified dose-response model constant |
| aR | = | Redlich–Peterson constant related to the affinity of binding sites |
| A | = | Clark model constant |
| C | = | contaminant concentration in the effluent |
| Ce | = | equilibrium concentration of contaminant in the aqueous phase |
| C0 | = | initial contaminant concentration in the influent |
| Ct | = | contaminant concentration in the effluent at time t |
| d | = | anion-exchange fiber dose |
| g | = | Redlich–Peterson constant related to the adsorption intensity |
| k1 | = | pseudo-first-order rate constant |
| k2 | = | pseudo-second-order rate constant |
| kBA | = | Bohart–Adams rate constant |
| Ke | = | equilibrium constant (dimensionless) |
| KF | = | Freundlich constant related to the removal capacity |
| KL | = | Langmuir constant related to the affinity of exchange sites |
| KR | = | Redlich–Peterson constant related to the adsorption capacity |
| Mf | = | mass of fiber packed into the column |
| 1/n | = | Freundlich constant related to the removal intensity |
| N0 | = | removal capacity per unit volume of fixed-bed |
| Q | = | flow rate |
| Qm | = | maximum removal capacity |
| qe | = | amount of contaminant removed (removal capacity) at equilibrium |
| qeq | = | contaminant removal capacity in the column experiment |
| q0 | = | removal capacity per unit mass of fiber |
| qt | = | amount of contaminant removed at time t |
| qtotal | = | amount of contaminant removed in the column experiment |
| r | = | Clark model rate constant |
| R | = | gas constant ( = 8.314 J mol−1 K−1) |
| R2 | = | determination coefficient |
| SAE | = | sum of the absolute error |
| T | = | temperature |
| U | = | linear flow velocity |
| yc | = | removal capacity calculated from the model |
| ye | = | removal capacity measured from the experiment |
| = | average measured removal capacity | |
| Z | = | bed depth |
| α | = | Elovich initial adsorption rate constant |
| β | = | Elovich adsorption constant |
| χ2 | = | chi-square coefficient |
| = | change in Gibbs free energy | |
| = | change in enthalpy | |
| = | change in entropy |