As (III) and As (V) Adsorption on Magnetite Nanoparticles: Adsorption Isotherms, Effect of pH and phosphate, and Adsorption Kinetics

Nanomaterials (typically 1~100nm in diameter) have been of considerable environmental attention due to their small particle size and large surface area. They have attracted great attention in recent times as potential materials which can be used for removal of heavy metals like arsenic from groundwater. For developing such a system it is extremely important to assess its adsorption characteristics of ions in water and wastewater. In the present study, the commercially procured magnetite nanoparticles (MNPs) have been assessed for arsenic (III) as As2O3 (arsenous oxide) & arsenic (V) as Na2HAsO4.7H2O (sodium arsenate) ions adsorption using NaOH solution in deionized water through laboratory batch experiments. The apparent particle size of MNPs was 20- 30 nanometer (nm). Batch adsorption tests were carried out under different conditions (e.g. varying pH [range 3 ~ 10], presence of competing anions i.e. PO4 3-) in order to evaluate the suitability of MNPs for use as arsenic adsorption materials in water. The result showed that the effect of pH on adsorption of both arsenite and arsenate did not appear to follow the same trend in Langmuir and Freundlich isotherms. Adsorption of arsenate was more than that of arsenite for pH<6.0 under similar conditions. At pH>6.0, the adsorption of arsenite on MNPs was a little higher than arsenate. Adsorption of arsenate was maximum at around pH 4.0; as pH increased further, adsorption decreased gradually. Similar but less pronounced trend was observed for the adsorption of arsenite on MNPs. The effect of pH on adsorption of arsenic could be explained by the aggregation characteristics of MNPs and charge on the aqueous arsenic species. Adsorptio