Performance of FeS synthesized within the porous media for in-situ immobilization of arsenic under varying water chemistry and groundwater conditions

The objectives of the study are (i) to assess arsenic immobilization efficiency by in-situ synthesized FeS within the porous media under varying solution chemistry and (ii) the performance evaluation of FeS-sand matrix in removing arsenic under natural groundwater conditions. To achieve the objectives, column experiments were performed where FeS was synthesized within the porous media in-situ. Then the As (III) or As (V) solution was injected within the column, and the effluents were collected to measure arsenic (As) and iron (Fe) concentrations. The groundwater samples were collected from seventeen locations in West Bengal, India, and were characterized. The As removal efficiency by FeS-sand matrix from the selected groundwater samples was studied in the batch and column system. The result showed that a significant amount of arsenite [As (III), 71.7–74.9%] was immobilized in the FeS synthesized porous media. The solution pH and the concentration of As (III) have an insignificant effect on immobilizing As (III) in the porous media system in the pH range of 6–8. Arsenate [As (V)] immobilization was not very promising under the reducing condition by in-situ synthesized FeS in the porous media. The As (V) removal was slightly better at pH 6 (26.9%) compared to pH 8 (11.7%). The occurrence of As in the groundwater (ranging from 0.78 μg/L to 376 μg/L) of the region was found to be associated with aluminum (Al) and Fe. The As removal by FeS-sand matrix showed better performance at pH 6 (40.7 ± 8.6%) compared to that of pH 8 (29.2 ± 15.6%) in the batch system. The immobilization of As increased significantly (83%) when the As-contaminated groundwater (376 μg/L) was injected into the porous media containing in-situ synthesized FeS. The concentration of Fe also reduced significantly (<160 μg/L) at the effluent after 2 PVs, indicating a limited risk of release of Fe. Overall, it could be stated that in-situ synthesized FeS in the porous media has the potential to immobilize As under a reducing environment within a range of pH under the groundwater conditions.