Green synthesis of high-surface-area pseudo-boehmite from high-aluminum alkaline wastewater via a novel cross-flow rotary carbonation process

Developing a novel cross-flow rotary carbonation (CFRC) technology. • Efficient Synthesis of High-Performance Pseudo-Boehmite (PB). • Thermodynamic analysis defines optimal PB window: T < 300 K, pH 10.4–13.0. • CFRC‑derived PB achieves 455 m²/g specific surface area, 1.26 cm³ /g pore volume. • Per ton PB products can reduce > 38 t alkaline wastewater with > 98% Al recovery. The aluminum industry generates large volumes of high-aluminum alkaline wastewater, yet efficient recovery of aluminum from such streams remains a challenge. In this study, we develop a novel cross-flow rotary carbonation (CFRC) process that integrates an ultra-fine atomizing gas disk with rotational stirring to decouple the mass transfer and crystallization stages, significantly enhancing gas-liquid reaction efficiency. Thermodynamic analysis reveals that the optimal conditions for pseudo-boehmite (PB) formation are T < 300 K and pH 10.4–13.0. Orthogonal experiments identify the key synthesis parameters: 0.1 mol/L NaAlO 2 , caustic ratio of 1.5, endpoint pH of 10.5, CO 2 flow rate of 0.5 L/min, and stirring speed of 350 rpm. Under these conditions, the CFRC-derived PB exhibits exceptional textural properties with a specific surface area of 455 m²/g, pore volume of 1.26 cm³ /g, and average pore size of 13.86 nm, representing a 94% increase in surface area over conventional batch stirring carbonation. Notably, NaAlO 2 concentration is the dominant factor; concentrations above 0.3 mol/L promote competitive gibbsite formation and deteriorate the pore structure. The process achieves over 98% aluminum recovery and reduces alkaline wastewater discharge by more than 38 tons per ton of PB produced, offering a green and efficient route for resource valorization. Download: Download high-res image (194KB) Download: Download full-size image