FIELD AND LABORATORY INVESTIGATIONS OF GROUNDWATER ARSENIC SEQUESTRATION IN BIOGENIC PYRITE AT AN INDUSTRIAL SITE IN FLORIDA

Pumping groundwater from arsenic (As)-contaminated aquifers has exposed millions, especially those in developing regions, to high doses of the toxic metalloid. Previous studies have discovered cost-effective techniques to remove As from groundwater by stimulating sulfate-reducing bacteria (SRB) and forming biogenic arsenic pyrite. This study improves upon these past methods by demonstrating the removal of groundwater As using SRB bioremediation at an industrial site in Florida.

This study developed a ferrous sulfate and molasses mixture to engender arsenian pyrite formation and sequester arsenic for nine months. In June 2018, the mixture was injected into eleven wells upgradient of the arsenic plume to promote full-scale remediation of the site. Groundwater and precipitated biomineral samples were collected from June 2018 to March 2019. X-ray diffraction (XRD), X-ray fluorescence (XRF), electron microprobe (EMP), and scanning electron microscope (SEM) analyses confirm that most of the As was sequestered in arsenian pyrite, which rapidly precipitated within two weeks of the injection as euhedral crystals and spherical aggregates (framboids) 1-30 μm in diameter.

The analyses also demonstrate that the arsenian pyrite contains 0.03-0.89 wt% of arsenic, with >80% of the groundwater As successfully removed by SRB biomineralization. As such, the injection scheme and remediating mixture reduced As concentrations to near or below the site’s clean-up standard of 0.05 mg/L within nine months. Considering these results, the study is close to optimizing an affordable method for removing dissolved arsenic at industry settings, with hopes for future utilization in developing communities.