Acid-resistant ferrihydrite-spent grain composites for enhanced as and Sb removal from acid mine drainage

Acidic wastewater contaminated with arsenic (As) and antimony (Sb) from antimony mining poses serious risks to surrounding ecosystems. Conventional iron-based materials for As/Sb removal often exhibit limited effectiveness under acidic conditions. To address this limitation, we developed a biomass modification strategy and synthesized a ferrihydrite-spent grain composite (FH-SG). Leveraging silicate and phosphate release from spent grains (SG), FH-SG exhibits excellent acid resistance. Moreover, ferrihydrite (FH) is uniformly dispersed on the surfaces of SGs, which inhibits their aggregation, enhances their active site reactivity, and markedly improves their arsenic and antimony remediation capacity. FH-SG has an adsorption capacity of 184.62 mg/g for As and 195.03 mg/g for Sb, which are 2.0 and 1.7 times greater than those of pure FH, respectively. As validated by simulated and field mining wastewater tests, the FH-SG-based retention barrier enables efficient As and Sb interception, with removal efficiencies stable over 95% (As) and 96% (Sb) at initial concentrations of 0.05-12 mg/L (As) and 0.92-120 mg/L (Sb), respectively. This system achieves satisfactory treatment performance under variable field conditions, including fluctuations in pH (3-7), rainfall intensity (20-60 mm/h), and concentrations (As: 0.05-12 mg/L; Sb: 0.92-120 mg/L). This approach overcomes the pH limitations associated with conventional treatment materials and offers a viable engineering solution for the remediation of acidic mining wastewater.