Characterization of arsenate and chromate removal from industrial wastewater by modacrylic anion exchange fibers

Abstract

This thesis aims to characterize the removal of arsenate and chromate from industrial wastewater by modacrylic anion exchange fibers. The physicochemical features of three anion exchange fibers (KanecaronTM KC31, SA, and SA2) and the factors that influence on removal of arsenate and chromate by the fibers were carefully examined. Field emission scanning electron microscopy (FESEM) images indicate that three fibers were micron-sized and cylindrical. The result of energy dispersive X-ray spectroscopy (EDS) revealed that the fibers are composed of carbon (C), nitrogen (N), oxygen (O) and chloride (Cl). Anion exchange capacity analysis showed that the pristine KC31 has 4.70 mmol/g of functional groups (free amine form), SA has 1.15 mmol/g of functional groups (fully protonated amine), and SA2 has 2.65 mmol/g of those (1.34 mmol/g of protonated amine and free amine form the others). From the results of pH experiments, As(V) removal by KC31 was highest at pH 4 (9.480 mg/g) and Cr(VI) at pH 2 (47.89 mg/g). As(V) removal by SA was highest at pH 10 (9.753 mg/g) and Cr(VI) at pH 4 (47.16 mg/g). In case of SA2, As(V) removal was highest at pH 10 (8.419 mg/g) and Cr(VI) at pH 6 (48.99 mg/g). The maximum removal capacity for As(V) of three fibers from Langmuir models were 47.16 mg/g (KC31), 47.19 mg/g (SA), and 38.05 mg/g (SA2). The maximum removal capacity for Cr(VI) of the fibers from Langmuir models were 250.2 mg/g for KC31, 162.5 mg/g for SA, 161.0 mg/g for SA2. At kinetic experiments, the fibers could reach equilibrium in reaction with As(V) and Cr(VI) in an hour. Arsenate or chromate adsorbed to fibers was successfully washed off with NaCl solutions, resulting in little changes of removal capacity over five adsorption-desorption cycles. Considering high heavy metal removal ability in acidic condition and large ion exchange capacity, KC31 was chosen as the proper adsorbent for two in order to treat acidic mining wastewater and chromium-plating rinse water. Columns filled with KC31 treated 1,145 mg of As(V) (flow rate : 1.0 mL/min), 2,890 mg of Cr(VI) (flow rate : 0.5 mL/min), and 2,390 mg of Cr(VI) (flow rate : 1.0 mL/min) under flow-through conditions. This study indicates that the anion exchange fibers are effective in removing arsenate and chromate in wastewater.