Upcycling kaolin bleaching wastewater into a biogenic Fe-based nanocomposite for selective rare earth elements recovery.

Iron-based adsorbents are predominantly synthesized from chemical iron salts, leading to additional resource consumption and secondary environmental burdens. In contrast, the conversion of iron-containing industrial waste into functional recovery materials has received limited attention. This study addresses the dual challenges of hazardous kaolin bleaching wastewater disposal and REE resource loss by developing a novel "waste-derived material for waste treatment" strategy. Specifically, we employed kaolin bleaching wastewater as an unconventional iron source to construct a sustainable bio-inorganic composite, FeNMs@DIRB, enabling simultaneous resource recycling and pollution control. The key innovation lies in utilizing dissimilatory iron-reducing bacteria (DIRB) to biosynthesize FeNMs@DIRB in situ, where microbial components prove indispensable for performance. Results demonstrate that DIRB successfully reduced Fe (II) from wastewater to form FeNMs, with 3D-EEM analysis confirming that microbial dissolved organic matter participated in nanomaterial formation and surface immobilization. The composite exhibited inherent selectivity (Gd > Y > La) in simplified systems, and achieved >95% removal for heavy REEs (Tb, Ho, Er, Yb) in real mining wastewater containing 12 REEs, maintaining selectivity under complex conditions. Notably, FeNMs@DIRB maintained satisfactory adsorption-desorption performance over three consecutive cycles and showed lower iron leaching across pH 4.0 and 8.0, confirming its structural stability and reusability. These results establish FeNMs@DIRB as a robust, selective adsorbent derived entirely from waste streams, offering a sustainable paradigm for REE recovery from complex industrial effluents.