Evaluation of injection schedule for synthesizing iron-sulfide within the porous media for immobilizing arsenite: In-situ remediation approach for arsenic in groundwater

Abstract

The main objectives of the study are, (i) to assess the possibility of synthesizing ferrous sulfide (FeS) in-situ within the natural sand packed porous media, (ii) to evaluate the extent of arsenite [As(III)] immobilization in the FeS containing natural porous media, and (iii) to evaluate the fate of iron (Fe) during immobilization of As (III) and its implication on the porosity. Several column experiments are performed, where ferrous sulfate (FeSO4) and sodium sulfide (Na2S) solution are injected alternatively in the porous media for synthesis of FeS with/without porous media being pre-saturated with As(III). Then As(III) solution is injected from one end. The results indicate that FeS can be effectively synthesized throughout the column. The immobilization of As(III) is also very high (>80% up to 17 PVs) in those cases. With As(III) pre-saturated condition, the injection of 20 mM reagents for 1.5 PVs shows the optimal result for immobilization of As(III) (>72% retained up to 35 PVs). In this case, though the relatively high amount of Fe has mobilized along with As(III) at the initial stage, however towards the later stage, no Fe is detected at the outlet, and almost 60% of injected Fe is retained within the porous media.