Physical Stability of Carboxymethyl Cellulose Stabilized Ferrous Sulfide Nanoparticles in Simulated Groundwater Under Anaerobic Conditions and the Corresponding Effect on Mercury Removal

Ferrous sulfide (FeS) nanoparticles have been extensively applied to remove heavy metals from soil and groundwater. This study considered the effects of aging, pH, and humic acid (HA) on the physical stability and mercury uptake of carboxymethyl cellulose stabilized ferrous sulfide nanoparticles (CMC-FeS) in simulated groundwater under anaerobic conditions. The coating of negatively charged CMC onto the surface of FeS improved the stability of FeS particles. Over aging, zeta potential and hydrodynamic diameters of CMC-FeS was increased at 60 d and then remained constant over 90 d. The dissolved Fe 2+ percentage was within the range of 1.0–1.7%. The mercury uptake was decreased from initial 3116.3 to 2972.0 mg/g (i.e., a 4.6% decrease) over 90 d. Higher pH rendered more negative CMC-FeS surfaces and lower pH led to the partial dissolution of CMC-FeS. As a result, the hydrodynamic diameters of CMC-FeS were enhanced with the increase of pH. The mercury uptake was raised sharply from 2587.0 mg/g at pH 4.2 to 3116.3 mg/g at pH 7.5–10.5. As HA concentration was increased from 0 to 10 and further to 20 mg/L, zeta potential was increased from initial -35.5 to -31.5 mV and then declined to -33.1 mV. Meanwhile, hydrodynamic diameters were increased from 327.4 to 387.7 nm and then declined to 354.8 nm. Increasing the HA from 0 to 5 mg/L decreased the mercury uptake by 9.5%. This study suggests that the physical stability of CMC-FeS and corresponding removal effectiveness of mercury should be taken into consideration for successful in situ groundwater remediation. Graphical Abstract