In-situ bio-nano FeS synthesis by sulfate-reducing bacteria for concurrent REE recovery from rare earth mine wastewater: Ternary coupling of biological reduction, chemical precipitation and adsorption co-precipitation

In-situ bio-nano FeS synthesis on SRB cell walls eliminates ex-situ nanoparticle production. • Ternary coupling: biological reduction tunes chemical precipitation for 76.2% REE recovery. • Dynamic bio-nano interface: -NH₂/S=O/-OH/-COOH complexation drives chemisorption (R 2  = 0.999). • Five-cycle reusability (80.7% capacity): practical robustness for continuous mining effluents. • Concurrent REE recovery and sulfate reduction: process intensification for dual pollutant control. The effective recovery of rare earth elements (REEs) from rare earth mine wastewater is a crucial issue for the sustainable utilization of resources and environmental protection. This study demonstrated the concurrent recovery of REEs from mining wastewater by utilizing sulfate-reducing bacteria (SRB) to synthesize FeS nanoparticles in situ. SEM-EDS, XRD and XPS showed that bio-nano FeS (nFeS) precipitated on cell walls within 48 h, forming SRB-nFeS-EPS composites that sequestered 76.2% of total REEs-significantly higher than SRB alone (56.1%), abiotic nFeS (48.3%) or extracellular polymeric substances (EPS) (7.7%). SRB efficiently reduced SO₄ 2− to S 2− in rare earth wastewater (the utilization rate of SO₄ 2− reached 56.7% at 24 h), and simultaneously, S 2− and Fe 2+ underwent chemical precipitation to form nFeS (50–200 nm). A pseudo-second-order (PSO) model (R 2  = 0.999) and five-cycle reusability (80.7% capacity retained) indicated chemisorption dominance and practical robustness. FTIR and 3D-EEM suggested that microbial -NH₂ groups may complex with S O and -OH/-COOH on the nFeS surface, contributing to combined complexation and ion-exchange. Pearson correlation analysis further highlighted C-OH and -NH₂ functional groups ( r  ≥ 0.95) and the S 2− -Fe 2+ couple ( r  = 0.95) as potential key factors governing REE sequestration and biomineralization synergy. The process is governed by a dynamic ternary coupling of biological reduction, chemical precipitation and adsorption co-precipitation, whose transition point defines the optimum bio-nano interfacial synergy. The findings offer a low-energy route for precise, in-situ REE recovery from sulfate-rich mining effluents.