Utilizing phosphogypsum-derived CaAl LDH-chitosan to remove Pb2+ from oil/gas field wastewater: Adsorption behavior and competitive mechanism

In this work, a novel calcium-aluminum layered double hydroxide-chitosan composite gel bead (LDH-CS) was synthesized for the efficient removal of Pb 2+ from high-salinity oil/gas field wastewater. The successful manufacture of CaAl-LDH by coprecipitation was achieved by utilizing CH 3 COONa to activate PG as an alternative to traditional calcium sources, thereby supporting the value-added use of industrial solid waste. Furthermore, the excellent compatibility between CS and LDH was confirmed through multiple characterization techniques, including SEM/EDS, FT-IR, XRD, and XPS. The greatest adsorption capability of LDH-CS was 827.9±9.6   mg   g -1 under the optimal conditions of 0.2   g   L -1 dosage, pH of 5, and 25 °C, as confirmed by batch experiments. Fixed-bed experiments confirmed that LDH-CS exhibits outstanding selective adsorption performance in high-salinity wastewater systems from actual oil/gas field, achieving a 99% removal efficiency for Pb 2+ . Compared with traditional powder adsorbents, the efficiency of solid-liquid separation after adsorption is substantially improved by embedding LDH powder in chitosan matrix in LDH-CS gel bead. This design prevents secondary pollution from suspended particles and ensures heavy metal release levels are well below safety limits. LDH-CS provides a practical, efficient and cost-effective technical solution for the treatment of lead-containing wastewater.