Nanoremediation of soil contaminated with Arsenic and Mercury

Researchers in Spain recently published a paper describing the utilization of nanoremediation technology to clean-up soil at the Brownfield site heavily contaminated with arsenic and mercury.

The research draws on a several lab-scale experiments that have shown the use of nanoscale zero-valent iron (nZVI) to be effective in reducing metal(loid) availability in polluted soils.

The core-shell model of zero-valent iron nanoparticles. The core consists of mainly zero-valent iron and provides the reducing power for reactions with environmental contaminants. The shell is largely iron oxides/hydroxides formed from the oxidation of zero-valent iron. The shell provides sites for chemical complex formation (e.g., chemosorption).

The researchers evaluated the capacity of nZVI for reducing the availability of As and Hg in brownfield soils at a pilot scale, and monitored the stability of the immobilization of these contaminants over a 32 month period. The researchers contend that their study is the first to apply nZVI to metal(loid)-polluted soils under field conditions.

In the study, two sub-areas (A and B) that differed in pollution load were selected, and a 5 m2 plot was treated with 2.5% nZVI (by weight) in each case (Nanofer 25S, NanoIron). In sub-area A, which had a greater degree of pollution, a second application was performed eight months after the first application.

Overall, the treatment significantly reduced the availability of both arsenic and (As) and mercury ((Hg), after only 72 h, although the effectiveness of the treatment was highly dependent on the degree of initial contamination.

Sub-area B (with a lower level of pollution) showed the best and most stable immobilization results, with As and Hg in toxicity characteristics leaching procedure (TCLP) extracts decreasing by 70% and 80%, respectively. In comparison, the concentrations of As and Hg in sub-area A decreased by 65% and 50%, respectively.

Based on the findings, the researchers contend that the use of nZVI at a dose of 2.5% appears to be an effective approach for the remediation of soils at this brownfield site, especially in sub-area B.