Remediation of zinc-contaminated groundwater by iron oxide in situ adsorption barriers – From lab to the field

Abstract

Heavy metals such as zinc cannot be degraded by microorganisms and form long contaminant plumes in groundwater. Conventional methods for remediating heavy metal-contaminated sites are for example excavation and pump-and-treat, which is expensive and requires very long operation times. This induced interest in new technologies such as in situ adsorption barriers for immobilization of heavy metal contamination. In this study, we present steps and criteria from laboratory tests to field studies, which are necessary for a successful implementation of an in situ adsorption barrier for immobilizing zinc. Groundwater and sediment samples from a contaminated site were brought to the lab, where the adsorption of zinc to Goethite nanoparticles was studied in batch and in flow-through systems mimicking field conditions. The Goethite nanoparticles revealed an in situ adsorption capacity of approximately 23 mg Zn per g Goethite. Transport experiments in sediment columns indicated an expected radius of influence of at least 2.8 m for the injection of Goethite nanoparticles. These findings were validated in a pilot-scale field study, where an in situ adsorption barrier of ca. 11 m × 6 m × 4 m was implemented in a zinc-contaminated aquifer. The injected nanoparticles were irreversibly deposited at the desired location within <24 h, and were not dislocated with the groundwater flow. Despite a constantly increasing inflow of zinc to the barrier and the short contact time between Goethite and zinc in the barrier, the dissolved zinc was effectively immobilized for ca. 90 days. Then, the zinc concentrations increased slowly downstream of the barrier, but the barrier still retained most of the zinc from the inflowing groundwater. The study demonstrated the applicability of Goethite nanoparticles to immobilize heavy metals in situ and highlights the criteria for upscaling laboratory-based determinants to field-scale.

Removal of Arsenic in Groundwater Using Fe(III) Oxyhydroxide Coated Sand: A Case Study in Mekong Delta, Vietnam

“…This kinetic study c adsorption of As(III) onto FeOOH coated sand was a multi-step process inv cal adsorption on the external surface and chemical binding with FeOOH re sand surfaces (chemical adsorption). This result agrees with previous lite outlines that the pseudo-second-order model represents a better adsorption The previous study revealed that the adsorption mechanism of arsenic on surface was a favorable chemical interaction between adsorbent and adsor permeable adsorptive barriers [12].…”

“…This result agrees with previous literature, which outlines that the pseudo-second-order model represents a better adsorption kinetic [12,15]. The previous study revealed that the adsorption mechanism of arsenic on a metal oxide surface was a favorable chemical interaction between adsorbent and adsorbate [11] and permeable adsorptive barriers [12].…”

“…This finding has also been pointed out in previous research [15]. However, another study revealed that Langmuir isotherm is the best fit for heavy metal adsorption onto nanoparticles of iron hydroxide [12]. Our kinetic investigation revealed strong evidence of a multi-step adsorption mechanism of As(III) onto FeOOH coated sand, in which pseudo-second-order was well fitted to the experimental data.…”

“…The sorption isotherms were compared graphically against Langmuir and Freundlich models. The Langmuir and Freundlich equations were adapted from Shoppert et al [12], expressed as the following:…”

“…It was also suggested that mixing iron particles with sand media may improve the removal of arsenic in solution [10]. Iron, ferric oxide, and iron-based materials have been well-documented as effective adsorbents for As removal from aqueous solution [10,11] or in situ remediations of zinc contaminated groundwater [12]. However, a number of challenges still exist in practice, such as low removal rates, as well as the presence of iron nanoparticles in the water [11].…”