Removal of Arsenic from Synthetic Groundwater Using Sulfur-Enhanced Cement-Based Filter Media

Arsenic-contaminated groundwater affects millions worldwide. A cement-based filter medium (CBFM) can be used to remediate heavy metals from groundwater. Recently, the desulfurization of flue gas in coal-fired power plants has increased sulfur content in fly ash, exceeding standard limits for use in normal concrete, thereby limiting beneficial reuse. This study investigated arsenic remediation by CBFM samples produced with high-sulfur fly ashes, waste synthetic gypsum, sodium sulfide, and elemental sulfur. Hardened concrete was batch tested in arsenic-contaminated deionized (DI) water and synthetic groundwater (SG) to elucidate ion competition. Arsenic removal exceeded 90% for all CBFM specimens in DI water, apart from sodium sulfide samples. In SG, elemental-sulfur and high-sulfur fly ash CBFM mixtures had 60%-85% removal at all tested concentrations. Scanning electron microscopy and X-ray diffraction spectroscopy showed a uniform distribution of arsenic, indicating high diffusivity throughout the cementitious paste. Arsenic removal occurred in two primary mechanisms: precipitation through the formation of calcium arsenate complexes and adsorption onto calcite, ettringite, and monosulfate. This research could lead to the use of CBFM as a readily available and waste valorizing remediation tool for arsenic-impacted areas.