Removal of phosphate by ferrihydrite composites formed from bacterially oxidized Fe(III)-solutions mixing MnCl2 or polyaniline

In this study, ferrihydrite composites of MnO 2 /Fh and PANI/Fh could form from bacterially oxidized Fe(III)-solutions mixing MnCl 2 (Mn/Fe =1) and polyaniline (PANI, 10 mg) at pH 8.0 −10.0, respectively. They could be used to remove P from the (waste)waters. The prepared MnO 2 /Fh wwas identified as Fh, γ-MnO 2 and γ-MnOOH phases by XRD, FTIR and XPS, and the other composite was PANI/Fh. Adsorption processes fitted to the first/second-order rate models and Weber-Morris intraparticle diffusion model (R 2 ranging in 0.920–0.999), and were spontaneous, endothermic and random. Isothermal adsorptions could be well described by Langmuir model (R 2 of 0.991–0.997) and Freundlich model (R 2 of 0.933 −0.979). The maximal P (10 mg/L) adsorption capacities ( Q e ) were 99.3 mg/g (PANI/Fh) and 84.3 mg/g (MnO 2 /Fh), while that of Fh was 53.6 mg/g at pH7.0. There were the wide pH ranges for PANI/Fh (3.0 −11.0) and MnO 2 /Fh (3.0 −8.0), and the presence of CO 3 2- ion declined P removal efficiencies. The main adsorption mechanisms were electrostatic attraction, ion exchange, and surface complexation. Two Fh composites still had the better abilities of treating P-containing neutral river waters after three regenerations. It provides the potential approaches for preparing Fe-composites and removing P using waste bacterial Fe(III)-solutions.