Encapsulation and Enhanced Phosphate Removal of ZCP@Alg Hydrogels Spheres by ZnCr-LDHs in Situ Growth on Seafoam Oxide Precursor

In recent years, the problem of eutrophication has intensified in lakes and rivers, and the cause is mainly due to the phosphate discharge from human life and production. In order to address excessive emissions of phosphate, a number of phosphate removal methods have been gradually derived. In this paper, metal oxide precursor (CMO) was synthesised by using acid etching solution and calcium salts. The powder adsorbent was synthesised by in situ growth of ZnCr-LDHs nanomaterials on CMO, named as ZCL/CMO. The ZCL/CMO composite was successfully encapsulated within a hydrogel framework comprising sodium alginate (SA) and polyaspartic acid (PASP), with Zr4+ serving as a crosslinking agent, resulting in the formation of ZnCr-LDHs/CMO/PASP@Zr-Alg spherical hydrogel spheres (ZCP@Alg). This approach offers a novel method for the efficient and stable removal of phosphorus from aqueous environments. The ZCP@Alg spherical hydrogel adsorbent was evaluated through scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR). The effects of solution pH, adsorption time, initial phosphate concentration, temperature and other anions on phosphate adsorption were executed. The results indicated that the ZCP@Alg adsorbent exhibited high adsorption capacity (219.12 mgP/g) and removal efficiency for phosphate. Even in the presence of various co-existing ions, the ZCP@Alg adsorbent maintained effective adsorption performance. Furthermore, over 80% of the adsorption capacity was preserved after five cycles of adsorption. The analysis of experimental data indicate that electrostatic attraction, intraparticle diffusion, surface complexation, and anion exchange mechanisms are involved in the phosphorus removal process using ZCP@Alg spherical hydrogel adsorbent. This study presents a novel synthesis method for adsorbents designed to enable waste-to-waste conversion and address the challenges associated with the solid-liquid separation of powdered adsorbents.