Copper ions removal in water by sodium alginate/sludge-derived humic acid aerogel: Adsorption mechanism and removal effect.

In this work, the sludge-derived humic acid (SHA), extracted from the remaining sludge of landfill leachate, was utilized to modify sodium alginate (SA) and prepare SA/SHA aerogel. The adsorption characteristics and underlying mechanisms of Cu(II) by SA/SHA aerogel in aqueous solutions were systematically investigated. The findings revealed that SA/SHA aerogel exhibited superior adsorption capabilities, with a maximum adsorption capacity for Cu(II) reaching 188.38 mg/g. The results aligned well with the pseudo-second-order kinetic model and the Langmuir isotherm model, indicating a uniform distribution of adsorption sites on the aerogel's surface, primarily driven by chemisorption-mediated monolayer adsorption of Cu(II). An examination of heavy metal leaching during the adsorption process confirmed the absence of secondary contamination in the solution after SA/SHA treatment. Studies on the presence of co-ions indicated that monovalent cations had a minimal impact on the selective adsorption of Cu(II) by SA/SHA aerogel, whereas divalent cations exerted a more significant influence. Furthermore, SA/SHA aerogel retained its structural integrity without disintegration even after five cycles of adsorption-desorption. Characterization techniques indicated that the adsorption mechanism of SA/SHA aerogel was dominated by complexation reactions and ion exchange of cations, supplemented by redox reactions.