Magnetic nanoparticles for removing inorganic arsenic species from waters: A proof of concept for potential application

Inorganic arsenic is considered one of the most critical and severe environmental problems due to its high toxicity even at low levels of exposure, causing serious health problems. Humans can be exposed to arsenic mainly through inhalation, ingestion of food and water, especially in certain areas where water comes into contact with arsenic-bearing minerals. For natural geological reasons, water in some areas of the world may contain more arsenic than usual. For these circumstances, the development of methods for the removal of arsenic from water has been of increasing interest in recent years. This work presents an optimised removal of As(III) and As(V) from water by the in situ formation of ferrite (Fe3O4) nanoparticles, leading to the adsorption of this element in the Fe3O4 structure. In addition, the magnetic properties of the nanoparticles facilitate their removal from the medium by a magnet. The experimental conditions of the process were optimised and the total removal of high concentrations of As(III) and As(V) in water was achieved in only two minutes and at 50 °C at basic pH, using 200 µL of a 0.2 M FeCl2·4H2O solution and 100 µL of a 0.1 M FeCl3·6H2O solution to form Fe3O4 in situ. The ferrite surface was characterised by field emission scanning electron microscopy before and after the arsenic removal process and by energy dispersive X-ray spectroscopy before the process. The study of adsorption kinetics and equilibrium isotherms reveals a Langmuir-type physicochemical process.