In the present work, superparamagnetic iron oxide nanoparticles (SPION) surface-coated with 3-mercaptopropanoic acid (3-MPA) were prepared and their feasibility for the removal of arsenate from dilute aqueous solutions was demonstrated. The synthesized 3-MPA-coated SPION was characterized using transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and Fourier transform infra-red spectrometry (FTIR). Separation efficiency of the coated nanoparticles and the equilibrium isotherm of arsenate adsorption were investigated. The obtained results reveal the arsenate adsorption to be highly pH-dependent, and the maximum adsorption was attained in less than 60 minutes. The resulting increase of 3-MPA-coated SPION adsorption capacity to twice the adsorption capacity of SPION alone under the same conditions is attributed to the increase of active adsorption sites. An adsorption reaction is proposed. On the other hand, efficient recovery of arsenate from the loaded nanoparticles was achieved using nitric acid (HNO 3 ) solution, which also provides a concentration over the original arsenate solution. HIGHLIGHTS• Feasibility of using SPION modified with 3MPA for the removal of As(V).• The adsorbent system results in an effective sorption for selective As(V) removal.• The adsorption capacity for As(V) is higher comparing with other adsorbent systems.• Adsorption mechanism has been proposed as the most suitable considering the results.

Nowadays, there is a wide variety of arsenic decontamination processes being adsorption processes the most efficient. In this concern, superparamagnetic iron oxide nanoparticles (SPION) have been proposed as an appropriate system to improve arsenic adsorption from acidic wastewater. The number of mines, the amount of ore processed, and thus the amount of mine (acid) wastewaters have been rapidly increased in recent decades. For this reason, arsenic removal from contaminated water is an important goal to accomplish environmental regulations. It is noteworthy that aggregation of these nanoparticles has been detected as the main difficulty, hindering the promising adsorption. In order to overcome this drawback, it is proposed a system to avoid aggregation based on nanoparticles dispersion into an appropriate supporting material. To this purpose, SPION have been fixed on a cellulosic sponge achieving a decrease of the aggregation state, an increase of the active centers, and consequently, arsenic adsorption increases. Experimental results report a lower aggregation of supported SPION over sponge than the observed in the non supported nanoparticles. At this point, a remarkable improvement in the sponge system adsorption capacity is observed in comparison with superparamagnetic nanoparticles in Post-print of: Morillo, D. et al. "Efficient arsenic(V) and arsenic (III) removal from acidic solutions with Novel Forager Sponge-Loaded Superparamagnetic Iron Oxide Nanoparticles" in Journal of Colloid and Interface Science, Vol. 453 (2015), p. 132. The final version is available at: DOI 10.1016/j.jcis.2015.04.048 2 suspension, reaching adsorption capacities about 2.1 mmol As/g SPION and 12.1 mmol As /g SPION for arsenite and arsenate, respectively at pH 3.8. Then, the developed system not only amends the aggregation problem but also keep their nanoproperties intact, making the system a suitable one for arsenic removal in acidic wastewater treatment. HIGHLIGHTS• Feasibility of using Forager Sponge-loaded SPION for arsenic removal.• Adsorption pH is the main parameter controlling the As(V) and As(III) removal.• SPION incorporation to Forager Sponge avoids the nanoparticles leaching.• Adsorption capacity for both arsenic species is higher than reported in literature.

Novel nanocomposites sorbents of superparamagnetic iron oxide nanoparticles (SPION) supported onto electrospun polyacrylonitrile nanofibers were synthesized with a simple and scalable method. The influence of both nanofiber size and SPION loading on As(V) adsorption capacity were studied and optimized. A maximum uptake capacity in batch mode tests of 32.5 mmol As(V)/g SPION while using an extremely low loading of only 2.9 mg of SPION/g of adsorbent was achieved. This represents a remarkable improvement of 36 times compared with SPION in suspension. The optimal material was tested in a continuous flow mode operation reaching to adsorption capacities of 851.7 mg As(V)/g of adsorbent at pH 3.8. It is also demonstrated that the new adsorbents can retain high performance when tested in real conditions with polluted wastewater from a lixiviation dump containing a large amount of competing anions (Cl -, F -) and interfering cations (K + , Na + , Mg 2+ , Ca 2+ ). Furthermore, no release of nanoparticles was observed during operation and the spent porous material can be compressed generating a small amount of solid waste that can be easily treated or stored.

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