Iron nanoparticles are efficient at removing mercury from polluted waters

Abstract Iron nanoparticles have been successfully used to remove metals from contaminated water. However, most research in this field has been performed with nanoparticles synthesized at the lab-scale. This study compares the capacity of three types of commercial iron nanoparticles, nanoscale zero-valent iron (nZVI), nano-magnetite (nFe3O4) and iron sulfide (nFeS) nanoparticles to remove Hg2+ from artificially contaminated water over a range of pH, dose, and time of contact. The three types of commercial nanoparticles removed Hg2+ from aqueous solutions being the immobilization processes stable for at least 48 h nZVI particles were faster and more efficient than nFe3O4 and nFeS in terms of Hg removal per unit of iron mass under the experimental conditions tested. The nZVI suspension (0.18 g Fe/L) immobilized 98% of Hg2+ after 15 min, removal ranging between 94 and 98% at the times tested, regardless of the pH (pH 3 to 9). X-ray photoelectron spectroscopy (XPS) analysis revealed that the mechanism by which nZVI immobilizes Hg2+ depends on the dose and includes reduction to Hg0 and adsorption and/or complexation of Hg2+ to the nZVI shell. In contrast, adsorption was the main mechanism for nFeS (1.6 g Fe/L) and nFe3O4 (3.9 g Fe/L), which removed almost 85 and 80% of Hg2+, respectively, after 3 h of contact. The effectiveness of nFe3O4 and nFeS increased slightly over time (until 48 h). The Hg2+removal capacity of nFe3O4 increased with the pH, while that of nFeS peaked at neutral and alkaline pH. Given these findings, the three types of iron nanoparticles emerge as potential candidates for the decontamination of Hg-polluted waters. The choice of nanoparticle depends on the efficacy required, the degree of pollution, the cost and length of the process.