Three-Dimensional Aerogel Beads Based on Magnesium-Modified Biochar and Sodium Alginate: A Sustainable...

The difficulty in recovering powdered biochar and its limited adsorption capacity are the main obstacles restricting the application of agricultural waste in cadmium (Cd²⁺) adsorption. To address these issues, magnesium-modified biochar (MBC)/alginate sodium (SA) aerogel beads were prepared through in situ cross-linking-gelation and freeze-drying techniques for the removal of Cd²⁺ from wastewater. The MBC/SA composite aerogel beads with excellent performance can be easily separated from the aqueous solution, avoiding the secondary pollution and equipment blockage caused by powdered adsorbents. The adsorption capacity of MBC/SA aerogel beads for Cd²⁺ under different conditions was analyzed and optimized. Additionally, the maximum adsorption capacity of Cd²⁺ by MBC/SA aerogel beads reached 289.6618 mg·g^-1, which fitted well with the Langmuir isothermal model (R² = 0.9911). Moreover, it was found that the adsorption process of Cd²⁺ on MBC/SA aerogel beads was spontaneous and endothermic, following pseudo-second-order kinetics (R² = 0.9935). Furthermore, even after 7 repeatable usage cycles, the adsorption efficiency of MBC/SA aerogel beads remained around 29.3%. This work proposes a simple and scalable manufacturing strategy to convert agricultural waste into an efficient adsorbent for wastewater treatment, adhering to the principle of sustainable development.