Adsorption–desorption mechanism of phosphate by immobilized nano-sized magnetite layer: Interface and bulk interactions

• Published in: Journal of colloid and interface science 2011-11, Vol.363 (2), p.608-614
• Main Authors: Zach-Maor, Adva, Semiat, Raphael, Shemer, Hilla
• Format: Article
• Language: English
• Subjects: activated carbon; active sites; Adsorption; binding sites; Composite adsorbent; desorption; Diffusion; Ferrosoferric Oxide - chemistry; Fixed-bed; ions; Iron oxide; Magnetite; Membranes, Artificial; Nanocomposites; Nanomaterials; Nanostructure; Nanostructures - chemistry; Particle Size; Phosphates; Phosphates - chemistry; Saturation; sodium hydroxide; Surface chemistry; Surface Properties; X-ray photoelectron spectroscopy; XPS
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2011.07.062

Interface and bulk adsorption and desorption mechanisms of phosphate by a homogenous porous layer of nano-sized magnetite particles immobilized onto granular activated carbon is presented. [Display omitted] ► Phosphate was initially bonded onto the Fe3O4 surface via bidentate complexation then diffused into the interior layer. ► Phosphate desorption, by alkaline eluent, was predominantly a surface reaction. ► Five successive fix-bed adsorption/regeneration cycles were successfully applied. ► Innovative correlation of adsorption–desorption performance with diffusion mechanism is presented. Phosphate adsorption mechanism by a homogenous porous layer of nano-sized magnetite particles immobilized onto granular activated carbon (nFe-GAC) was studied for both interface and bulk structures. X-ray Photoelectron Spectroscopy (XPS) analysis revealed phosphate bonding to the nFe-GAC predominantly through bidentate surface complexes. It was established that phosphate was adsorbed to the magnetite surface mainly via ligand exchange mechanism. Initially, phosphate was adsorbed by the active sites on the magnetite surface, after which it diffused into the interior of the nano-magnetite layer, as indicated by intraparticle diffusion model. This diffusion process continues regardless of interface interactions, revealing some of the outer magnetite binding sites for further phosphate uptake. Desorption, using NaOH solution, was found to be predominantly a surface reaction, at which hydroxyl ions replace the adsorbed phosphate ions only at the surface outer biding sites. Five successive fix-bed adsorption/regeneration cycles were successfully applied, without significant reduction in the nFe-GAC adsorption capacity and at high regeneration efficiency.