Development of iron oxide nano materials-based technology for arsenic remediation

Abstract

In 2005, the Colvin group proposed the use of magnetite nanoparticles for arsenic adsorption. This would allow the reduction of waste significantly with the additional advantage of magnetic-driven separation at low fields. However, despite the efforts of several groups around the world, the use of arsenic sorbents based in nanomaterials is not yet feasible. Still, the study of new iron-based nanomaterials for arsenic uptake has been increasing over the last years. During my PhD program, I have analyzed the performance of magnetite nanoparticles synthesized by several methodologies with both batch experiments and column tests and varying conditions including groundwater with high silica concentrations (Chapter 4). Silica is one of the most common interferences and dramatically decreases the arsenic removal capabilities. My work included the evaluation of arsenic removal capabilities on site (Salamanca, Mexico) and the comparison with commercially available arsenic sorbents under those difficult conditions− [SiO2] =85ppm and pH=8 (Chapter 3). In spite of the comparable performance of the nanoparticles to other commercial sorbents, their small-scale production and the lack of a simple filtration setup motivated us to design a material that could be used under real-world operation conditions. We proposed the use of clusters of nanoparticles in order to benefit of the properties of both the nanoparticles and the bulk material. The understanding of the mechanism of the synthesis, the effect that synthetic parameters have in the cluster size and unit size, and the corresponding effect in arsenic adsorption are discussed in Chapter 5. Currently, the most pressing needs for groundwater treatment is in developing countries; this forces the use of highly cost-effective strategies. In order to develop a material that can feasibly solve the needs on the field in an inexpensive way, one of the projects was to modify the kitchen synthesis of nanomagnetite previously introduced by our group. Even when in the past a cheap synthesis was achieved, it was a process with several steps and the nanoparticles were not able to absorb arsenic. In this work (Chapter 6), a one-pot synthesis is proposed and studies have shown that the nanoparticles thereby obtained have much better arsenic removal performance than the nanoparticles prepared by thermal decomposition making the material very promising. Even though the work proposed herein will not solve the problem of arsenic contamination, it provides a grasp of the requirements for the implementation of nanomaterials in water treatment technologies and narrows the gap between design of nanomaterials in the lab and their application on the field.