Three-Dimensional Aerogel Beads Based on Magnesium-Modified Biochar and Sodium Alginate: A Sustainable High-Performance Adsorbent for Efficient Removal of Cadmium from Wastewater

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 (<i>R</i>² = 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 (<i>R</i>² = 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.