Unlocking High Co-Removal Capacity for Phosphate and Arsenate in Wastewater: Synthesis, Performance, and Mechanism of Copper–Aluminum Layered Double Hydroxide

The development of high-efficiency adsorbents for the removal of phosphate and arsenate is of great significance in acid mine drainage remediation. Layered double hydroxides (LDHs), characterized by their tunable composition and structure, are ideal for constructing adsorbents with tailored chemical environments. Among them, copper–aluminum layered double hydroxide (CuAl-LDH), which primarily features atomically dispersed Cu species coordinated with Al atoms, is particularly promising due to the high affinity of its copper sites for these oxyanions. However, the strong Jahn–Teller distortion of Cu2+ has made the synthesis of phase-pure binary CuAl-LDH a longstanding challenge. This work addresses this fundamental synthesis barrier by developing a facile coprecipitation route for fabricating phase-pure CuAl-LDH. The synthesized material exhibited excellent performance, achieving maximum adsorption capacities of 451.1 mg/g for phosphate and 244.3 mg/g for arsenate, with rapid removal kinetics (achieving over 99% removal within 5 min). In simulated AMD containing both pollutants enabled near-complete co-removal, reducing the residual concentrations of phosphate and arsenate below 0.01 mg/L at an optimized dosage. Mechanistic studies (XRD, XPS, XAS, 27Al NMR, STEM-EDS) revealed a synergistic removal process involving interlayer anion exchange of NO3– by PO43–/AsV, surface complexation via Cu–O–P/As and Al–O–P/As bond formation, and electrostatic attraction on the positively charged surface under acidic to neutral pH. This work provides an efficient synthesis route for binary CuAl-LDH and elucidates its effective dual-anion removal mechanism for complex wastewater remediation.