Phosphate removal from aqueous solutions by a nano-structured Fe–Ti bimetal oxide sorbent

Abstract

Phosphate removal from water is of vital importance to control eutrophication. Adsorption is one of the most popular technologies for phosphate removal. In this study, iron oxide-based sorbents with different Fe/Ti molar ratios were synthesized by coprecipitation method. Results showed that the Fe–Ti bimetal oxide prepared with a Fe/Ti molar ratio of 20:1 was the optimal sorbent for phosphate removal. Transmission electron microscopic (TEM) image analyses indicate that the Fe–Ti bimetal oxide was nano-structured aggregates. The sorption kinetic data could be described better by the pseudo-second-order equation indicating its chemisorption nature. The boundary layer (film) diffusion was the rate-limiting step of sorption process. The equilibrium sorption data were well fitted with the Langmuir and Freundlich models. The phosphate sorption capacity calculated from Langmuir equation was 35.4mg/g at pH 6.8. Thermodynamics experiments showed that the phosphate sorption was spontaneous and endothermic. The results of ionic strength effect together with zeta potential, FTIR and XPS analyses demonstrated that the main mechanism of phosphate sorption was the replacement of surface hydroxyl groups (M–OH) by phosphate via formation of inner-sphere surface complex. The spent Fe–Ti bimetal oxide could be effectively regenerated by NaOH solutions.