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

Abstract

This study, reports the rapid preparation of activated carbon (AC) modified phosphoric acid-activated geopolymer microspheres (C@PAAGMs) for fast adsorptive separation of ReO4− (as a chemical analogue of TcO4−). 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 ReO4− was reduced to ReO2, indicating that ReO4− reduction proceeded via chemical and physical adsorption routes. The effect of competitive ions on the adsorption of ReO4− followed an order of: NO3− > SO42− > Cl− > PO43−, 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 ReO4− from industrial wastewater.