Biochar/Mg-Al spinel carboxymethyl cellulose-La hydrogels with cationic polymeric layers for selective phosphate capture

Recently, biochar-related phosphate sorbents have been extensively investigated and achieved significant progress; however, there is still much room for enhancement on capturing performance and recovery of powdery ones after sorption. Herein, a new kind of adsorbent, in which biochar/Mg-Al spinel encapsulated in carboxymethyl cellulose-La hydrogels with cationic polymeric layers, was fabricated, aiming for integrating multi-advantages of each component for enhanced phosphate capture. Batch static experiments were correlated to the phosphate adsorption performance of the adsorbent. The maximum phosphate adsorption capacity of the adsorbent was 89.65 mg P/g at pH = 3. The Langmuir isotherm model and the pseudo-second-order kinetic model fitted well with the adsorption behavior of the adsorbent. More importantly, this composite adsorbent that integrated with biochar, Mg-Al spinel, cationic polymeric components exhibited favorable selectivity over coexisting anions (Cl^-, SO₄^2-, HCO₃^- and NO₃^-) and performed good reusability after five consecutive cycles. By virtue of the bead-like feature, fixed-bed column experiments demonstrated that the Thomas model fitted the breakthrough curves well under varied experimental conditions. The adsorption mechanism of phosphate on the designed composite adsorbent with multi-components could be described as the electrostatic attraction, ligand exchange and inner-sphere complexation, which might account for the efficient phosphate capturing performance.