Competitive adsorption of nitrate in fixed-bed column packed with bio-inspired polydopamine coated zeolite

Abstract

In this research natural zeolite clinoptilolite micro particles were modified with polydopamine nano-layer as bio-inspired biopolymer through an oxidative polymerization process. The coating thickness, thermal stability and the specific surface area of the adsorbent were investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), thermogravimetric analysis (TGA) and nitrogen adsorption/desorption isotherms. The coating thickness on the zeolite was estimated to be about 6 nm. The semi-synthetic adsorbent was used for the removal of nitrate anions (NO3−) from aqueous solution. The adsorption experiments were carried out in fixed-bed column. Two fixed-bed adsorption models, Thomas and Adams-Bohart, were applied to predict the breakthrough curves. Effect of experimental parameters such as pH, initial concentration of nitrate, bed height, temperature, and flow rate on the column efficiency was examined. The optimum values of the aforementioned factors were obtained at pH = 3; flow rate = 3 mL min−1; nitrate concentration = 150 mg L−1; temperature = 10 °C and bed height = 2.4 cm. The results showed that the surface modified zeolite exhibits a good potential for nitrate removal from aqueous solution. Furthermore, the nitrate removal was performed in the presence of competing anions such as bicarbonate, sulfate and phosphate. The results revealed that the competing anions (PO43−, SO42− and HCO3−) affect the nitrate uptake performance of the column in various extent. Finally, the reusability tests showed that the exhausted sorbent can be regenerated and reused at least three times for nitrate adsorption.