Synchronously construction of hierarchical porous channels and cationic surface charge on lanthanum-hydrogel for rapid phosphorus removal

• Published in: Environmental research 2023-11, Vol.236, p.116730-116730, Article 116730
• Main Authors: Wang, Siying, Wang, Yili, Dong, Shuoxun, Li, Xiaolin, Liu, Chenyang
• Format: Article
• Language: English
• Subjects: Bifunctional adsorption sites; Electrostatic interaction contribution; La–P complex; Phosphate; Regeneration; Unsaturated adsorption
• ISSN: 0013-9351; 1096-0953
• DOI: 10.1016/j.envres.2023.116730

Phosphorus (P) removal from wastewater is critical for ecosystem operation and resource recovery. To facilitate the recycling of the used absorbents through balancing their adsorption and desorption performance on P, in this work, a novel porous magnetic La(OH)3-loaded MAPTAC/chitosan (CTS)/polyethyleneimine (PEI) ternary composite hydrogel (p-MTCH-La(OH)3) with enhanced bifunctional adsorption sites was synthesized by simultaneous dissolution of pre-embedded CaCO3 and CTS powder, followed by grafting PEI and loading La. Hierarchical porous channels promoted good dispersion of La(OH)3, bringing an excellent P adsorption capacity of 107.23 ± 4.96 mg P/g at neutral condition. PEI grafted with CTS increased the surface charge and enhanced the electrostatic attraction, which facilitated the desorption of P. The porous structure and abundant active sites also facilitated rapid adsorption with an adsorption rate constant of 0.1 g mg−1 h−1. p-MTCH-La(OH)3 maintained effective P adsorption despite co-existence with competing substances and after 5 cycles. Further mechanistic analysis indicated that La–P inner sphere complexation and LaPO4 crystalline transformation were the main pathways for P removal. However, electrostatic interactions contributed 17.5%–46.7% of the adsorption amount during the first 30 min of rapid adsorption, enabling 92.8% of the adsorbed P at this stage to be desorbed by alkaline solution. Based on the variations of adsorption and desorption capacity with adsorption time, a rapid unsaturated adsorption of 1–2 h was proposed to facilitate the recycling of the adsorbent. This study proposed a method to promote P adsorption and desorption by enhancing bifunctional adsorption sites, and proved that p-MTCH-La(OH)3 is a promising phosphate adsorbent. [Display omitted] •The maximum P adsorption capacity of p-MTCH-La(OH)3 was 107.23 ± 4.96 mg P/g.•The affinity of p-MTCH-La(OH)3 toward P was strong over the pH of 3–11.•Simultaneous dissolution of CaCO3 and chitosan promoted bifunctional sites.•Rapid unsaturated adsorption in 1–2 h facilitated p-MTCH-La(OH)3 recycling.•P adsorbed mechanisms were electrostatic attraction and La–P ligand exchange.