Synthesis optimization of hybrid anion exchanger containing triethylamine functional groups and hydrated Fe(III) oxide nanoparticles for simultaneous nitrate and phosphate removal

Abstract

The excessive discharge of nutrient into natural water can cause detrimental eutrophication effect to the ecological system. For the nutrient removal, there is quite challenging to simultaneously remove trace phosphate usually exists at level <2.0 mg/L and high concentration of nitrate exists at level 100 mg/L under the presence of competing background ions. In this study, the novel hybrid polymeric anion exchanger impregnated with hydrated Fe(III) oxide (HFO) nanoparticles (HA520E-Fe) was synthesized, characterized, and evaluated preliminary performance for co-removal of trace nitrate and phosphate. HA520E-Fe composes of dual functional groups; triethylamine that selective for nitrate ions through the ion exchange mechanism and HFO nanoparticles that selective for phosphate adsorption through Lewis acid based (LAB) interactions. During the HFO loading process, low dielectric constant solution preferred ethanol was used as aqueous medium to reduce the Donnan exclusion effect (i.e., repulsion between Fe3+ ions and triethylamine functional groups) and thus enhances HFO formation inside the parent anion exchange resin. Upto 5 loading cycles can enhance the phosphate removal capacity without sacrifice the nitrate take up capacity. HA520E-Fe was further characterized by SEM-EDX, HR-TEM, XRD, and EXAFS. The HFO nanoparticles were uniformly dispersed throughout the pore structure at approximately 12.45 %w/w with size well below 50 nm. From XRD diffractograms, the HFO inside the material retains high surface area of amorphous phase even after 5th cyclic sorption-desorption runs. Preliminary performance studies using equilibrium batch tests including effect of feed pH, pHPZC, and sorption isotherms, and fixed-bed column runs were also evaluated. The novel HA520E-Fe exhibits high removal capacity for simultaneous sorption of nitrate and phosphate and can be applied in various applications such as secondary effluent, including aquacultures wastewater.