Montmorillonite decorated with amorphous iron-(hydr)oxides nanoparticles for effective phosphate removal and recovery from wastewater

Recovery and reuse of phosphorous (P) is key for reducing eutrophication and alleviating the stress on rock-phosphate mining. Here, montmorillonite decorated with nano-sized amorphous iron (hydr)oxides (FeOx-MT) was used to remove phosphate from secondary effluent. The reactive nanoparticles were anchored to montmorillonite via wet deposition to create a composite with active sites that do not aggregate or lose activity in the solution. The resulting material was found to specifically adsorb phosphate from wastewater effluent, yet easily release it at moderately basic pH. Under high ionic strength and low pH, the capacity of FeOx-MT was found to be high, reaching 92.3 mg-P/g-Fe. At pH values above nine, the phosphate ions were easily desorbed, suggesting high regeneration ability under relatively benign conditions. Kinetic measurements and adsorption isotherms under different conditions indicate that the adsorption mechanism is based on specific ligand interactions that are highly pH dependent. P-removal and recovery from real secondary effluent was assessed in column experiments and compared to a commercially available granular iron)hydr(oxide (GFH). The continuous column experiments highlighted the superiority of FeOx-MT over several consecutive cycles, allowing for regeneration of the composite surface. Overall, the unique surface properties of the material make it interesting from both a mechanistic and an applicative standpoint.