New Functionalized Magnetic Materials for As 5+ Removal: Adsorbent Regeneration and Reuse Juan Saiz, Eugenio Bringas, and Inmaculada Ortiz* Dept. Ingenierías Química y Biomolecular, ETSIIyT, Universidad de Cantabria, Avda Los Castros s/n, 39005 Santander, Spain * S Supporting Information ABSTRACT: The presence of arsenic in natural water is one of the most important pollution problems worldwide. Functionalized magnetic silica/magnetite nanoparticles (M3) have been reported as effective materials for arsenate adsorption [Saiz et al., 2014]. Because the process economy might be limited by the solid reuse, this work aims at the analysis of the regeneration and reusability of arsenate loaded M3 materials. The influence on the desorption and readsorption efficacies of the type and concentration of the regeneration agent, HCl or NaOH, and the sorbent refunctionalization steps (F1 is protonation of amino groups, F2 is coordination of Fe 3+ ) is analyzed. Desorption with HCl is concentration dependent with maximum efficacies at 0.25 mol L -1 . Solutions of NaOH 10 -3 mol L -1 provided the best desorption performance; however, the regeneration of the solid needed of two stages of refunctionalization (F1 and F2). Furthermore, regenerated materials under alkaline conditions reported adsorption yields of arsenic around 90%. ■ INTRODUCTION Water treatment is one of the most important fields of adsorption application. This technology reports several advantages over other traditional water treatment alternatives such as precipitation because of its simple design, its easy operation and maintenance, and its ability to selectively remove the pollutants up to low concentration levels. Literature collects a large number of innovative adsorption materials with ability to remove heavy metals and organic compounds from aqueous solutions. In spite of the great importance of the adsorbent regeneration stage for the process economy, it is much less studied than the adsorption stage, and the available data are still rare in the case of the removal of heavy metals, such as arsenic solubilized in natural water. 2-15 Groundwater contamination with arsenic (arsenate and arsenite) is a recognized environmental hazard that affects a large proportion of the world’s population that does not have access to adequate sources of water for drinking. 16 The most affected areas are West Bengal, Bangladesh, Taiwan, Northern China, and Argentina due to the weathering of rocks, the improper management of industrial wastes, the agricultural use of arsenic, and so forth. 4,17 Due to its toxicity for humans, the arsenic level in drinking water was limited by the WHO (World Health Organization) and the EPA (Environmental Protection Agency) as 10 μgL -1 . 18,19 Nowadays, the use of nanomaterials for the development of adsorption processes is an emerging area of study due to the unique characteristics of these materials because of their small size, large surface area, ease of functionalization, and so forth. Different nanoadsorbents have been reported as efficient materials to remove arsenic, that is, activated alumina, chitosan, 14 nanozerovalent iron, 20,21 maghemite and hematite nanoparticles, 22-25 akaganeite, 9 silica-based materials, or activated carbon. 26-28 In addition, the design of nano- adsorbents incorporating magnetic properties, that is, using as adsorbent magnetite nanoparticles 25,29 or magnetic composite materials, 30,31 is a promising alternative to facilitate the recovery of the solid dispersed in the liquid phase by application of a high gradient magnetic field. 5 In general, adsorption materials for metal removal should be stable, efficient, cost-effective, and reusable. Under the selected operation conditions, adsorbents have a finite removal capacity; when it is achieved, the material should be regenerated for reuse or managed at the end of its life depending on the process economy. 32 Even though several end-of-life alternatives for exhausted adsorbents such as solid combustion have been reported in the literature, in the case of arsenic-loaded materials, thermal alternatives are not feasible because arsenic oxides are volatile and can easily escape to the atmosphere. 33 On the other hand, regeneration processes aiming at restoring the sorbent close to its initial properties should be low-cost, allowing the solid reuse during the maximum number of cycles and, thus, decreasing the costs of the overall separation process. However, the eluted regeneration solution is a waste stream that should be managed. As arsenic has limited markets its recovery and further reuse from the regeneration solution may not be cost-effective, these streams are usually managed by the following strategies: (i) concentration and containment, (ii) dilution and dispersion, (iii) application of destructive techniques to remove the contaminant, and (iv) stabilization of the pollutant by material encapsulation, which is the most extensively reported option in the literature. 33,34 In particular, arsenate desorption has been studied with different solutions, most of them based on the influence of pH on the process. 4 Sodium hydroxide 2-10,35 and strong mineral Special Issue: Ganapati D. Yadav Festschrift Received: March 3, 2014 Revised: April 10, 2014 Accepted: April 11, 2014 Article pubs.acs.org/IECR © XXXX American Chemical Society A dx.doi.org/10.1021/ie500912k | Ind. Eng. Chem. Res. XXXX, XXX, XXX-XXX