Kinetic, equilibrium and thermodynamic studies for phosphate adsorption to magnetic iron oxide nanoparticles
Introduction
The synthesis and application of magnetic nanoparticles to water and wastewater treatment have attracted considerable attention in recent years [1]. Magnetic nanoparticles can be used as adsorbents for water and wastewater treatment and separated from aqueous medium through magnetic separation [2], [3], [4], and among the various magnetic nanoparticles, maghemite (γ-Fe2O3) and magnetite (Fe3O4) are the iron oxides observed to be useful [5]. Several researchers applied magnetic iron oxide nanoparticles to remove contaminants from aqueous solutions [1], [6], [7]. Pan et al. [8] removed mercury from an aqueous solution by mercapto-functionalized magnetite nanoparticles. Badruddoza et al. [9] fabricated magnetite nanoparticles functionalized with carboxymethyl-β-cyclodextrin to remove copper ions. Wang et al. [10] investigated the sorption kinetics and mechanism of copper to nanoscale magnetite. Iram et al. [11] removed neutral red dye from an aqueous solution using magnetite hollow nanospheres. Wang et al. [12] synthesized the composites of magnetite nanoparticles and gellan gum to adsorb heavy metals.
Phosphate is an essential macronutrient in aquatic environments, but in excessive amounts, it causes eutrophication of reservoirs, lakes and coastal areas [13]. Effluent concentration of phosphate from wastewater treatment facilities and industrial plants must be controlled through chemical and biological techniques to meet the discharge limits [14], [15].
Researchers have used magnetic iron oxide nanoparticles for phosphate removal. For use as adsorbents to remove phosphate in batch and fixed-bed experiments, Zach-Maor et al. [16], [17] impregnated magnetite nanoparticles (<4 nm) to granular activated carbon. They performed kinetic and equilibrium isotherm model analyses of the batch sorption data. Pan et al. [18] synthesized nano-sized magnetite particles (40.3 nm) stabilized with sodium carboxymethyl cellulose to immobilize phosphate in soils; they observed the adsorption kinetics of phosphate on the magnetite nanoparticles along with the transportability of the nanoparticles in soils. de Vicente et al. [19] used magnetite nanoparticles (90.6 ± 1.2 nm) to adsorb phosphate from aqueous solutions and examined the adsorption isotherms and the reusability of the nanoparticles. Daou et al. [20] investigated the phosphate adsorption mechanisms of magnetite nanoparticles (40 nm) via infrared spectra, X-ray photoelectron spectroscopy and Mössbauer spectrometry analyses. Further studies are required to definitively determine the phosphate removal capability of magnetic iron oxide nanoparticles.
The aim of this study was to investigate the removal of phosphate from aqueous solutions using magnetic iron oxide nanoparticles. Kinetic, equilibrium and thermodynamic experiments were performed to characterize the phosphate to the magnetic nanoparticles. Sorption kinetic and equilibrium isotherm models were used for the data analysis.
Section snippets
Synthesis of magnetic iron oxides nanoparticles
Magnetic iron oxide nanoparticles were synthesized by a coprecipitation method. An alkali solution of sodium hydroxide (NaOH, 6 mol) was added drop-wise with intensive stirring at room temperature into a 500 mL solution of FeSO4⋅7H2O (0.25 M) and FeCl3⋅6H2O (0.5 M) to obtain a pH of 7.6. The resulting precipitates were aged at 60 °C for 18 h and then washed thoroughly with deionized water to remove any excess sodium. The washed precipitates were then oven-dried at 150 °C for 6 h and then pulverized in
Characteristics of phosphate sorption
The characteristics of phosphate sorption to the magnetic nanoparticles are shown in Fig. 2. The phosphate removal by the magnetic nanoparticles as a function of adsorbent dose (initial P concentration = 2 mg P L−1; reaction time = 24 h) is shown in Fig. 2a. The percent removal increased with increasing adsorbent dose from 0.1 to 2.0 g L−1. At the adsorbent dose of 0.1 g L−1, the percent removal was 19.0%, increasing to 98.5% at 0.6 g L−1. The percent removal reached 100% at 0.7 g L−1. The sorption capacity
Conclusions
In this study, phosphate removal by magnetic iron oxide nanoparticles was examined. The results demonstrate that the magnetic nanoparticles were effective in the removal of phosphate with the maximum sorption capacity of 5.03 mg P g−1. The phosphate removal was relatively constant at acidic solution pH, whereas the phosphate removal decreased sharply as the solution pH approached a highly alkaline condition. The thermodynamic tests indicate that phosphate sorption to the magnetic nanoparticles
Acknowledgements
This work was supported by the KIST (Korea Institute of Science and Technology) Institutional Program (Project No. 2E24280). Also, this research is supported by the National Research Foundation of Korea Grant funded by the Korea Government (MSIP) (2013, University-Institute cooperation program).
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