Development of lanthanum carbonate-loaded ion exchange resin for selective phosphate removal

Abstract

The use of lanthanum for phosphate removal has gained increasing attention due to its strong affinity toward phosphate over a wide pH range. In this regard, although lanthanum hydroxide exhibits promising phosphate removal ability, its practical application remains limited due to certain technical issues including its structural instability and leaching. To circumvent these issues, a lanthanum carbonate-based adsorbent was developed in this study. Lanthanum carbonate@anion exchange resin (LC@AER) and lanthanum hydroxide@anion exchange resin (LH@AER) beads were first prepared through in-situ precipitation using identical bead-to-precursor mass ratios. LC@AER beads were chosen for further study as they displayed better adsorption capacity and stability, and the bead-to-precursor mass ratio was further optimized to improve performance and stability. LC@AER (1:2) beads exhibited a maximum adsorption capacity of 77.43 mg-P/g and excellent selectivity toward phosphate in the presence of various co-existing anions. Experiments using river water indicated high phosphate removal efficiency, demonstrating potential for treating river water. Investigations revealed key differences in phosphate binding mechanisms for batch and column experiments. In batch setting, phosphate is primarily captured through ligand exchange and inner-sphere complexation. However, in continuous flow operation, surface precipitation and electrostatic attraction (between phosphate and quaternary ammonium) become increasingly important for binding phosphate, which may affect phosphate recovery efficiency and must be accounted for in process design. Overall, the findings indicate that LC@AER (1:2) beads are promising for phosphate removal in real water samples.

Date of Award	2022
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	Irene Man Chi LO (Supervisor)