Mercury is a pervasive, persistent, and toxic contaminant widely found in surface waters and groundwater. Mercury is regulated with a mandatory discharge limit of 10 µg/L for wastewater, and a maximum contaminant level of 2 µg/L in drinking water. To mitigate human exposure and comply with these regulatory criteria, cost-effective treatment technologies have been consistently sought. In this work, we developed a new class of stabilized iron sulfide (FeS) nanoparticles sodium carboxymethyl cellulose (CMC) as a stabilizer, and tested the material for enhanced removal of aqueous mercury (Hg2+). CMC at ³0.03 wt.% fully stabilized 0.5 g/L of FeS (i.e. CMC-to-FeS molar ratio ³0.0006). FTIR spectra suggested that CMC molecules were attached to the nanoparticles through bidentate bridging and hydrogen bonding. Increasing the CMC-to-FeS molar ratio from 0 to 0.0006 enhanced mercury sorption capacity by 20%; yet, increasing the ratio from 0.0010 to 0.0025 diminished the sorption by 14%. FTIR and XRD analyses suggested that precipitation (formation of cinnabar and metacinnabar), ion exchange (formation of Hg0.89Fe0.11S) and surface complexation were important mechanisms for mercury removal. A pseudo-second-order kinetic model was able to interpret the sorption kinetics, whereas a dual-mode isotherm model was proposed to simulate the isotherms, which considers both precipitation and adsorption. High mercury uptake was observed over the pH range of 6.5-10.5, whereas significant capacity loss was observed at pH&lt;6. High concentrations of Cl- (&gt;106 mg/L) and organic matter (5 mg/L as TOC) modestly inhibited mercury uptake. The immobilized mercury remained stable when preserved for 2.5 years at pH above neutral. The immobilized mercury is expected to much less bioavailable, and thus, more resistant to biological methylation.

Immobilization of mercury by stabilized iron sulfide nanoparticles: Reaction mechanisms and effects of stabilizer

249th National Meeting (2015)

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