Phosphate separation from aqueous solution using a chitosan-based biodegradable ion exchanger

To remove phosphate (P_i) from wastewater, a novel, low-cost adsorbent was developed by immobilizing copper ions (Cu2+) on a naturally available biopolymer chitosan. The copper ions bound to chitosan through its complex formation with the amino and hydroxyl groups in the polymer chain. This complex formation could reduce the size of the hydrogels and thus increase the density of the natural biopolymer. The chelating interaction between nitrogen and copper enabled the intra- and inter-molecular cross-linking, thereby improving the physical and chemical stability of the polymeric ligand exchanger. Most importantly, Cu²⁺ ions could serve as the active functional group for Pi removal from aqueous solution. The polymeric ligand exchanger displayed a greater affinity with P_i rather than sulfate due to the electrostatic and Lewis acid/base interactions between immobilized Cu²⁺ and P_i, regardless of the solution pH. Batch adsorption experiments showed that the polymeric ligand exchanger had the maximum capacity of approximately 85 mg/g in Pi solutions. The polymeric ligand exchanger could also be applied to a fixed-bed column reactor, demonstrating the high performance on the Pi removal from aqueous solutions.