Arsenic elimination using iron nanoparticles supported on ion exchange resine

C. A. NEYERTZ; G. MENDOW; C. A. QUERINI; B. S. SÁNCHEZ

Santa Fe

Conferencia; VI San Luis Conference; 2018

INTEC, UNL, CONICET

Arsenic is a contaminant harmful to health that occurs in water either by natural or anthropogenic origin. Its presence is observed in several countries and in a large area of our country with values above 10 gL‐1, which is the limit allowed by the World Health Organization. The aim of this work is the synthesis of nanoparticles of iron inside commercial anion exchange resins (Diaion® WA30 and Amberlite PWA5) for the treatment of arsenic contaminated water. The materials are obtained through different preparation methods: the direct exchange of iron and subsequent oxidation1, and the reaction of iron with an oxidant agent previously exchanged2. In the first case, FeCl4‐ (formed previously by a solution of FeCl3 and NaCl) is exchanged in the resin and then the nanoparticles (Nps) are precipitated inside the support using a 25% NaOH solution. In the second method, the resin is saturated with MnO4‐ anions, which then act as oxidizing agent of FeSO4. In this way, iron Nps dispersed in the polymer network and capable of adsorbing arsenic are obtained. Samples with different % Fe were prepared using both commercial resins as support for the first method and only the PWA5 resin for the second preparation method. The samples were characterized by optical microscopy. It was observed that the distribution of theiron inside the spherical particle of resin produces the coloration of them, which were originally white. The analysis by FTIR determined that the chemical treatment during the preparation did not generate deterioration of the support. The study by XRD indicated the formation of different iron species (FeOOH, Fe2O3, Fe3O4). The absence of marked peaks in the diffractograms of some samples indicated the presence of nanometric particles. The presence of these particles could be observed by transmission electron microscopy (TEM). The arsenic adsorption capacity of the samples was analyzed in a continuous flow system with synthetic water containing 75 ppm As+5 and other competing anions, typically present in water. The arsenic concentration was measured by Atomic Absorption with hydride generation (FI HG AAS). Among the samples studied, the maximum treated volume of water with concentration lower than 10 ppb was obtained for those samples supported over PWA5 with high %Fe (7.3 and 9.6%). The best result was obtained with the 9,6%Fe/PWA5 adsorbent, which was able to treat over 4700 volumes. Therefore. this sample was used to treat a real water (obtained from Progreso‐town in Santa Fe, and containing 78 ppb As). In this case, the treated volume was lower than the obtained with synthetic water (1200). This result could be ascribed to the presence of humic acids, the higher sulfates content (98 ppb vs. 50 ppb of synthetic water), or microbial growth. This issue needs to be further investigated. The regenerability of this adsorbent was studied by treating two different portions of the used sample with NaOH 0.1M or 1M, in continuous flow. After passing 1 L of each solution through the samples, the regeneration rates were 17% and 89%, respectively. Therefore, it can be said that the Fe/PWA5 adsorbent could be effectively regenerated by NaOH treatment. Although the study of the elimination of arsenic in these samples is in development, the good effect of Fe on PWA5 resin can be induced from these preliminary results.