Efficient chloride removal by macroporous pseudo-boehmite: Performance and mechanistic insights in diverse cationic environments

Flue gas desulfurization (FGD) wastewater represents a significant environmental challenge due to its high chloride ions (Cl⁻) content, which accelerates corrosion and compromises operational issues in coal-fired power plants. The Friedel's salt precipitation (FSP) method is a promising zero liquid discharge (ZLD) strategy for Cl⁻ removal. However, the conventional process using NaAlO₂ faces intrinsic limitations due to Na⁺-induced side reactions and low aluminum utilization rate (AUR). This study introduces macroporous pseudo-boehmite (MPB) as a novel, sodium-free aluminum source to overcome these restrictions and achieve highly efficient Cl⁻ removal via cation-specific coordination pathways. Systematic investigation of MPB dissolution under varied hydrochemical conditions revealed enhanced aluminum leaching kinetics. Batch tests in NaCl, CaCl₂, and MgCl₂ solutions demonstrated that Ca²⁺/Mg²⁺ significantly enhanced Cl⁻ removal (up to 88 %) and AUR (∼59 %) by facilitating direct FS formation, avoiding charge compensation, and inhibiting competing byproducts. Kinetic and phase analyses indicated that Na⁺ accelerated initial dissolution but favored by-product (Ca₃Al₂OH₁₂) formation at high temperatures, whereas Ca²⁺/Mg²⁺ enhanced FS stability. The MPB-based FSP process achieved faster equilibration (20 min at 80 °C) and higher efficiency, positioning it as a sustainable alternative for ZLD implementation of hazardous high-chloride wastewater.