Abstract The pollution of phosphate has been regarded as a serious global environmental issue in the past decade. In this study, mesoporous feroxyhyte (δ-FeOOH) nanoparticles were synthesized and δ-FeOOH/Fe(II) system was employed for the removal of phosphate. Effect of initial pH as well as conversion of Fe(II)/Fe(III) in solution were investigated. Brunauer-Emmett-Teller analysis, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy were employed to characterize the δ-FeOOH nanoparticles before and after reaction in order to reveal the possible mechanism. Results indicated that δ-FeOOH/Fe(II) system showed a great removal performance (94.1%) for phosphate under acidic condition and the removal of phosphate by δ-FeOOH/Fe(II) system was a process which simultaneously included adsorption and chemical precipitation. Phosphate removal by δ-FeOOH/Fe(II) system was endothermic, spontaneous and followed the Freundlich isotherm model and pseudo-second-order model. The great phosphate removal capability of the δ-FeOOH/Fe(II) system exhibited its potential as an effective method for phosphate immobilization in wastewater. Graphical abstract Unlabelled Image Highlights • Phosphate removal efficiency reached 94.1% at pH 3.0 by δ-FeOOH/Fe(II) system. • -OH groups on δ-FeOOH surface are beneficial to phosphate adsorption. • The in-situ generated Fe(III) in solution promoted the immobilization of phosphate. • Reaction process was endothermic and followed the Freundlich isotherm model. [ABSTRACT FROM AUTHOR]