Arsenic Removal by Nanoscale Magnetite in Guanajuato, Mexico

Abstract

Increasingly, cities in Latin America are recognizing the importance of drinking water quality on public health. A water assessment of Guanajuato, Mexico, and surrounding areas indicated naturally occurring arsenic in some wells above the Mexican drinking water standard of 25 lg/L and the World Health Organization recommendation of 10 lg/L. This initiated a collaborative effort with the city to evaluate a new arsenic removal method using high surface area magnetite sorbents. Nanoscale (20 nm) magnetite particles, previously shown to effectively adsorb arsenic in batch systems, were packed in sand columns to create a continuous treatment process. Design and operating variables were evaluated to confirm that magnetite-to-sand ratio and residence time most significantly affected arsenic breakthrough profiles. Subsequently, a pilot column with 456 g (ca. $2.50 USD) of a commercially available, food-grade magnetite (98 nm effective particle diameter) from a pigment manufacturer demonstrated removal of the equivalent arsenic contained in 1,360 L of Guanajuato groundwater. Although pH reduction dramatically improved arsenic adsorption in batch isotherms, no improvement in arsenic removal efficiency was observed when applied to pilot-scale, field columns in Guanajuato. Interference effects (e.g., from background silica) and changes to surface species over time may impact adsorption differently in column versus batch systems. Overall, this work represents one of the first pilot studies of a nanotechnology-enabled water treatment system, and it demonstrates the potential and additional challenges for taking nanoscale magnetite or other highly researched nanomaterials into a complex full-scale setting.

Environmental implications and applications of engineered nanoscale magnetite and its hybrid nanocomposites: A review of recent literature

“…More intriguingly, XANES and XPS results reveal complex redox transformation of the adsorbed As on MNPs exposed to air: Concomitant with the oxidation of MNPs, the oxidation of As(III) and MNPs is expected, but the observed As(V) reduction is surprising because of the role played by the reactive Fe(II) [290]. A pilot column test of a commercially available, food-grade magnetite (98 nm) has demonstrated removal of As(V) from Guanajuato, Mexico groundwater [291]. A magnetically separable nanomaterial Fe3O4-TiO2 eliminates the disadvantages of MNP agglomeration and iron leaching and takes advantage of the fact that TiO2 NPs are also effective As(V) and As(III) adsorbent [292].…”

Synthesis and Characterization of Magnetic Nanomaterials with Adsorptive Properties of Arsenic Ions

“…More recently, magnetite nanoparticles focused the attention of scientists as an adsorbent used for the removal of arsenic ions owing to their small size, large specific surface area, and magnetic properties [ 25 ]. Magnetite particles with size below 30 nm have superparamagnetic properties.…”

Synthesis of Magnetite Nanoparticles by Top-Down Approach from a High Purity Ore

“…Magnetite nanoparticles and their suspensions have shown widespread applications including wastewater treatment [1], heavy metal removal [2][3][4][5], magnetic recording devices [6,7], magnetic data storage devices [8], toners and inks for electrophotography [9,10], magnetic resonance imaging [11], bioseparation, targeted drug delivery [12][13][14][15], pigments [10], flocculants [16], and catalytic materials [16,17].…”