Removal of Arsenic(III) from Groundwater by Nanoscale Zero-Valent Iron

Abstract

Nanoscale zero-valent iron (NZVI) was synthesized and tested for the removal of As(III), which is a highly toxic, mobile, and predominant arsenic species in anoxic groundwater. We used SEM-EDX, AFM, and XRD to characterize particle size, surface morphology, and corrosion layers formed on pristine NZVI and As(III)-treated NZVI. AFM results showed that particle size ranged from 1 to 120 nm. XRD and SEM results revealed that NZVI gradually converted to magnetite/maghemite corrosion products mixed with lepidocrocite over 60 d. Arsenic(III) adsorption kinetics were rapid and occurred on a scale of minutes following a pseudo-first-order rate expression with observed reaction rate constants (K(obs)) of 0.07-1.3 min(-1) (at varied NZVI concentration). These values are about 1000x higher than K(obs) literature values for As(III) adsorption on micron size ZVI. Batch experiments were performed to determine the feasibility of NZVI as an adsorbent for As(III) treatment in groundwater as affected by initial As(III) concentration and pH (pH 3-12). The maximum As(III) adsorption capacity in batch experiments calculated by Freundlich adsorption isotherm was 3.5 mg of As(III)/g of NZVI. Laser light scattering (electrophoretic mobility measurement) confirmed NZVI-As(III) inner-sphere surface complexation. The effects of competing anions showed HCO3-, H4SiO4(0), and H2P04(2-) are potential interferences in the As(III) adsorption reaction. Our results suggest that NZVI is a suitable candidate for both in-situ and ex-situ groundwater treatment due to its high reactivity.

A radiotracer study of the adsorption behavior of aqueous Ba2+ ions on nanoparticles of zero-valent iron

“…It is proposed that the oxide layer, which is about 3-5 nm thick, protects the core of the particles against further oxidation and provides a means for the transport of mass and charge across it (e.g. [7,8,16]). In addition, it was further reported that the oxide layer consists not only of iron oxide but contains also boron (mostly in its +3 oxidation state), the thing responsible for enhancing the particle resistance against atmospheric attack and thus limiting the oxidation [22].…”

“…Comparatively, less effort was devoted to studying the adsorption of metal ions on NZVI. The ions investigated so far include As(III) and As(V) [7][8][9], Pb(II) [3], Cr(VI) [10], Ni(II) [11], and other ions [12]. No reports are present on the applicability of NZVI for radioactive isotopes which are important from radioactive waste management viewpoint.…”

Thiol-functionalised mesoporous silica-coated magnetite nanoparticles for high efficiency removal and recovery of Hg from water

“…The manufacture of these magnetic composite particles first requires creation of the nanoparticles and then modification of the surface to match the requirements and constraints of the proposed end use (Hu et al, 2006;Williams, 1994). Of interest in the current research are micro and mesoporous nanomaterials, as these have a high surface area and high porosity (Kanel et al, 2005); this coupled with high reactivity makes them useful as adsorbents in water and wastewater treatment. Functionalised nanoporous adsorbents are therefore now being studied with respect to their possible use in the removal of heavy metals from aqueous media (Da'na and Sayari, 2011;Mamadou et al, 2008;Shahbazi et al, 2010).…”

Adsorption behavior of arsenic onto protonated titanate nanotubes prepared via hydrothermal method

“…Arsenic exists in natural water predominantly as inorganic arsenate, As (V) and arsenite, As (III) [3][4][5][6][7]. Elevated concentrations of arsenic are found in groundwater in many regions around the world, which are caused by the release of arsenic from As-bearing sediments or anthropogenic sources [8][9][10].…”

“…An ideal adsorbent should have suitable particle size or uniformly accessible pores, high surface area, and physical and/or chemical stability [4]. Recently, nanoscale metal oxides such as mesoporous alumina [4], TiO 2 [8], and zero-valent iron [5] have attracted the attention of researchers, and they have shown great advantage towards arsenic removal.…”