Assessment of Selenate Adsorption from Industrial Wastewater Using Chloride-Type Layered Double Hydroxides

High Resolution Image Download MS PowerPoint Slide This study evaluates two chloride-type magnesium–aluminum layered double hydroxides (Cl–Mg–Al LDHs), specifically undoped ABL and iron-doped ABLm, for selenate remediation in high-salinity industrial wastewater featuring an extreme 39,814:1 sulfate-to-selenium ratio. Batch adsorption experiments and nonlinear regression modeling revealed a distinct capacity-affinity trade-off; while a reference lab-synthetic LDH yielded the highest maximum adsorption capacity ( q max ), Fe-doping drastically enhanced selenium binding affinity, yielding a significantly higher Langmuir constant (K L ) for ABLm (22.65 L/mmol) than ABL (9.66 L/mmol). Ion chromatography (IC) and X-ray diffraction (XRD) confirmed that both materials utilize an anion exchange mechanism that concurrently captures sulfate. Crucially, X-ray photoelectron spectroscopy (XPS) demonstrated that while ABL relies on weak electrostatic outer-sphere adsorption, ABLm facilitates a selective, reduction-coupled inner-sphere pathway. This mechanism transforms selenate into stable metal selenides (Se 2– ) and elemental selenium (Se 0 ) via Fe-mediated electron transfer. These findings show that transition-metal doping shifts adsorption from site quantity to high-affinity quality, providing a robust engineering strategy for selective selenium immobilization in complex industrial waste streams.