Continuous-Flow Removal of Arsenic in Drinking Water by Filtering down through Fe₃O₄@SiO₂ Magnetic Composite

Abstract

Natural contamination of world groundwater supplies with arsenic of volcanic origin has become a complicated and growing problem given current shortage of water. Maintenance cost of treatments that are based on ion exchange and reverse osmosis is considered high, in addition to the high production of sludge with such methods. On the other hand, efficiency of treatments employing coagulation/filtration is usually relative, depending on the method of application. Currently, emerging treatments that use nanotechnology are gaining relevance, due to their high efficiency and low cost. These methods are highly selective, with minimum generation of toxic wastes, as long as particle release into the environment is kept under control to avoid health risks. The present study developed filters with magnetic nanoparticles of Fe 3 O 4 (magnetite) supported on porous silica (Fe 3 O 4 @SiO 2 ) at a mass ratio of 2:1. The nanoparticles were synthetized by co-precipitation of Fe(II) and Fe(III) using NH 4 OH (ac) under inert atmosphere. Average sizes of 15 nm were obtained, measured by means of Transmission Electronic Microscopy (TEM) and characterized by X-ray Powder Diffraction (XRD); the magnetic power was qualitatively determined. The efficiency of the composite material (Fe 3 O 4 @SiO 2 ) was determined in a prototype laboratory with a height of 60 cm and a diameter of 5 cm, assembled with five filters of the composite material, with 1 g each filter. The filters were wrapped in resistant water-porous fabric to favor continuous flow at a ratio of 0.015 L/min. The test was performed with arsenic solutions at (43.7 ± 2.1 μg/L), similar to the amount present in water supplies currently treated in Costa Rica. The removal was completed in 7 minutes with 0 N.T.U and less than 10 μg/L arsenic concentration (maximum limit allowed in Costa Rica), quantified by Atomic Absorption Spectrometry with Hydride Generation. After the reaction filters, the prototype was assembled with cleaning filters at a ratio of 1:8. The final way out was through a magnetized tube to ensure that no nanoparticles were released outside with the water, thus contributing to nanotoxicology safety for people and the environment.