The contamination of drinking water with arsenic has been a great problem in several parts of Costa Rica during the last years. In regions such as Cañas, Bagaces, and Aguas Zarcas, there have been found wells with arsenic levels up to thirteen times the permitted value of 10 µg/L. The presence of this contaminant is a major concern because of its toxicological and carcinogenic effects on human health. The removal of heavy metals (including arsenic) in water can be accomplished using different approaches. The use of materials containing nanoparticles has attracted considerable attention in recent years. In particular, porous materials modified with Fe3O4 nanoparticles represent convenient removers. In such class of composites, the porous material represents a support with high surface area in which Fe3O4 nanoparticles are deposited, providing the ability to remove arsenic species (in natural waters, arsenic is mostly found in inorganic form as arsenite or arsenate oxyanions). Also, the magnetic behavior of these composites allows their retention using external magnetic fields. Several removers were synthesized using silica, bentonite, kaolinite, or diatomite as support, later modified with Fe3O4 nanoparticles. Typically, the composites were prepared as follows: 1) drying of the support, 2) dispersion of the support in a solution containing Fe(II) and Fe(III) cations under inert atmosphere, 3) co-precipitation of Fe(II) and Fe(III) cations using ammonium hydroxide as the precipitating agent, 4) washing with water until neutral pH. The resulting materials have support-magnetite weight ratios of 2:1 and were characterized using Scanning Electron Microscopy, Fourier Transform Infrared Spectroscopy, Raman Spectroscopy, Thermogravimetric Analysis and Differential Scanning Calorimetry, and X-Ray Powder Diffraction. Removal tests were performed in batch as well as in continuous flow. For the batch experiments, factors such as amount of remover, removal time, concentration of arsenic, and pH were evaluated. On the other hand, a scalable lab system was implemented to study the performance of the removers using continuous flow. For all the experiments, the arsenic content of the samples was determined using Hydride Generation Atomic Absorption Spectroscopy. Also, several test kits were validated using natural waters sampled from areas in Costa Rica with high arsenic levels, in order to have simple procedures to determine arsenic in the field, if required.

Application of porous materials modified with Fe3O4 nanoparticles for arsenic removal in drinking water

251st National Meeting (2016)

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