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Removal of arsenic in aqueous solution using magnetic spinel ferrite Fe3O4

Arsenic (As) in groundwater and contaminated drinking water has been a major health risk impact in Taiwan and southeast Asia countries. Arsenic has been a common added ingredient in production of various industries, including herbicide, pesticide, antiseptic, wood preservative, glass and ceramic-ware, metallurgy, leather, textile, dye, and rare metals. This can easily cause serious impacts on surrounding environments, in particular groundwater and drinking water contamination, and ecological systems if no proper waste managing strategy or controlling policy. Similar high level of As in groundwater has been reported in the Yun-Lin county in central and Chia-Nan costal plan in southwestern Taiwan. Magnetite (Fe3O4), so-called Ferrite, is a common Fe oxide with spinel structure. It has received wide attention internationally in recent year for its capability to adsorb As in aqueous solutions. However, paucity effort was dedicated to related researches in science community in Taiwan. In this proposal, we apply well developed hydrothermal method to synthesize nano-particle size of ferrite and to conduct a series of batch experiments to evaluate its capability to remove As in aqueous solution under various pH, T, solution/ferrite ratio and ion concentration conditions. Our major efforts in the past year are: (1) accomplish the optimal synthesizing conditions of magnetic nano-ferrite; (2) accomplish the characteristics analysis of magnetic nano-ferrite; and (3) accomplish some adsorption experiments for As removal by magnetic nano-ferrite. The preliminary results showed the synthesized magnetic nano-ferrite has a great potential for removal of As even under acidic conditions, where the As(V) removal efficiency could reach more than 95 % in five minutes. In pH 3-4, the As(V) removal efficiency could reach than 99.99 %. From the adsorption isotherm, As(V) adsorption capacities were determined to be 14.35, 10.12 and 4.88 mg/g at pH 3, pH 7, and pH 11, respectively. In order to investigate the feasibility of magnetic nano-adsorbents in natural groundwater, six As contaminated groundwaters were sampled and tested for As removal in the laboratory. The total dissolved As concentration ranges from 21.6 to 84.3 µg/L, indicating all of the these groundwaters were potentially As contaminated groundwater (WHO limit: 10 µg/L). Our synthesized nano-ferrite were applied to remove As in these samples in the laboratory and found As removing efficiency of more than 91.7 % in all cases. Currently we are further evaluating the feasibility in ferrite treatment of the polluted groundwaters in natural sites.
Magnetic nano-ferrite, Magnetic separation, Arsenate