Convenient preparation of activated carbon modified phosphoric acid-activated geopolymer microspheres (C@PAAGMs) for the efficient adsorption of ReO4−: Implications for TcO4− elimination

This study, reports the rapid preparation of activated carbon (AC) modified phosphoric acid-activated geopolymer microspheres (C@PAAGMs) for fast adsorptive separation of ReO 4 − (as a chemical analogue of TcO 4 − ). The microstructural aspects of C@PAAGMs before and after the modification and adsorption were characterized by SEM/EDS, XRD, BET, FTIR, particle size, Raman spectroscopy and XPS. Adsorption data were consistent with the pseudo-second-order model and Freundlich isothermal model. The actual maximum adsorption capacity was 65.64 mg/g of the AC. XPS, FTIR and XRD analyses showed that the C–H bond in 2gC@PAAGMs was converted to C–O bond, while ReO 4 − was reduced to ReO 2 , indicating that ReO 4 − reduction proceeded via chemical and physical adsorption routes. The effect of competitive ions on the adsorption of ReO 4 − followed an order of: NO 3 − > SO 4 2− > Cl − > PO 4 3− , while this order for real water was: tap water > surface water > seawater. 2gC@PAAGMs realized ultra-fast and highly efficient separation of solid-liquid within 10 s, which was many times higher than many reported state of the art adsorbents. Furthermore, 2gC@PAAGMs exhibited excellent column separation performance. Attributed to the low cost, fast solid-liquid separation and high efficiency, the newly designed 2gC@PAAGMs can be scaled up for the large-scale removal of ReO 4 − from industrial wastewater. • Preparation of different C@PAAGMs by suspension dispersion solidification method. • 2gC@PAAGMs have excellent dynamic adsorption performance. • 2gC@PAAGMs have certain recycling and rapid settling properties. • The adsorption of ReO 4 − by 2gC@PAAGMs includes physisorption and chemisorption.