Impact of ionic strength on goethite colloids co-transported with arsenite (As) through a saturated sand column under anoxic condition: Experiment and mathematical modeling.

The knowledge about co-transport of goethite and As to investigate the effect of goethite colloids on As transport under various degrees of seawater intrusion, particular extremely conditions, in groundwater environment is still limited. The main objective is to investigate the influence of seawater intrusion on the sorption, migration, and reaction of Asand goethite colloids into sand aquifer media under anoxic conditions by using the bench-scale and reactive geochemical modeling. The research consisted of two parts as follows: 1) column transport experiments consisting of 8 columns, which were packed by using synthesis groundwater at IS of 0.5, 50, 200, and 400 mM referring to the saline of seawater system in the study area, and 2) reactive transport modeling, the mathematical model (HYDRUS-1D) was applied to describe the co-transport of As and goethite. Finally, to explain the interaction of goethite and As, the Derjaguin-Landau-Verwey-Overbeek (DLVO) calculation was considered to support the experimental results and HYDRUS-1D model. The results of column experiments showed goethite colloids can significantly inhibit the mobility of As under high IS conditions (>200 mM). The R of As bound to goethite grows to higher sizes (47.5 and 65.0 μm for 200 and 400 mM, respectively) of goethite colloid, inhibiting As migration through the sand columns. In contrast, based on R value, goethite colloids transport As more rapidly than a solution with a lower IS (0.5 and 50 mM). The knowledge gained from this study would help to better understand the mechanisms of As contamination in urbanized coastal groundwater aquifers and to assess the transport of As in groundwater, which is useful for groundwater management, including the optimum pumping rate and long-term monitoring of groundwater quality.

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