Highly efficient copper ions removal by sodium alginate/sodium humate@Polyacrylamide: adsorption behavior and removal mechanism

In this work, sodium alginate/sodium humate @ Polyacrylamide (SA/SH@PAM) hydrogel beads were prepared using sodium alginate as encapsulant, sodium humate as filler, and polyacrylamide wrapped on the outer layer. Removal and recycling performance toward batch and column adsorption of Cu (II) was investigated. The results indicated that SA/SH@PAM had good removal behavior in the pH range of 3.0-6.0, with an optimal pH of 5.0. The maximum adsorption capacity of SA/SH@PAM beads could reach similar to 134.65 mg/g, which was 2.0 and 1.6 times higher than that of sodium alginate beads (SA) and sodium alginate/sodium humate beads (SA/SH), respectively. Pseudo-second-order kinetic model could fit experimental data better, indicating the chemisorption of Cu (II) on SA/SH@PAM surface. Isotherm and thermodynamics studies suggested that heterogeneous multilayer adsorption occurred on the surface of SA/SH@PAM and Cu (II) adsorption was a spontaneous and endothermic process. Thomas model was fitted better than Adams-Bohart model with breakthrough curves in a fixed-bed column system, signifying that internal and external diffusion was not the main factor limiting the adsorption efficiency of SA/SH@PAM. Characterization analysis (FT-IR, SEM, XPS, etc.) indicated ion exchange and the interaction of multiple functional groups (-COOH, -CO-NH-, etc.) with Cu (II) were the main adsorption mechanisms. Besides, SA/SH@PAM demonstrated good regeneration and anti-interference ability of co-existing ions. Overall, SA/SH@PAM is a potential adsorbent for Cu (II) removal from wastewater.