Microwave-enhanced green precipitation of hollow boehmite microspheres large-scalely and their efficiently dynamic adsorption for roxarsone removal

Roxarsone (ROX) as a phenylarsenic feed additive, causes markedly threats to human health and water environment, and the key to treat it by adsorption method is to develop green large-scale preparation method of low-cost and efficient adsorbent. Herein, boehmite microspheres with superior ROX removal performance were efficiently synthesized on a large scale via a microwave-assisted green liquid phase precipitation (MP) method by regulating the carbon chain length of carboxylate ester precipitants. Especially, the ethyl acetate (EA) with short chain length results in hierarchical boehmite hollow microspheres (S-MP-EA) composed of three levels including crystalline grain at the nanoscale, hierarchical mesoscale packing of the nanoflakes centering around 3.8 nm and 10.5 nm, assembly of a self-supporting hollow microspheres driven by ionic conduction heating of microwave. Its fixed-bed dynamic adsorption for ROX with an initial concentration of 200 mg·L −1 showed that 5 g powder maintained its complete removal for the first 51 h, while the 10 g granulated adsorbent with diameters of 4.0 ± 0.1 mm achieved removal efficiency more than 90 % over 121 h suggesting its superior adsorption capability and long-term stability. Its synergistic adsorption mechanisms involving hydrogen bonding, electrostatic attraction and pore filling were significantly enhanced by microwave-enhanced hydroxyl density, positively charged distribution, hierarchical hollow structure and mesoporous structure. Combined with aluminum utilization efficiency of 95.50 % under precipitation conditions at 60 °C for only 30 min with environmental-friendly and easily obtainable raw materials, our work provides alternative functional aluminas with engineering applicability for highly efficient adsorption of organic arsenic wastewater.