Removal of Arsenic and Mercury with Permeable Reactive Barrier Consisting of Iron Oxide Particles

Groundwater contamination by heavy metals such as arsenic (As) and mercury (Hg) is of a significant concern because the toxicity exhibited by these heavy metals can pose a severe threat to human health and the environment. In recent years, passive treatment technologies such as permeable reactive barriers (PRBs) have increased rapidly due to lower long-term operation and maintenance costs compared with the traditional active treatment technologies such as pump and treat.

Zero-valent iron (ZVI) has been one of the most widely used barrier materials in PRBs due to its effectiveness in removing a wide range of contaminants. However, barriers consisting of ZVI often experience reduction in porosity, chemical reactivity, and hydraulic conductivity over time due to corrosion and mineral precipitation. This study presents the evaluation of alternatives to ZVI (such as Fe₃O₄ and Fe₂O₃) that can be used in the PRBs. The specific objective of the study is to improve the fundamental understanding of the performance of individual corrosion products for As and Hg removal. Batch experiments have been carried out and it was found that the removal efficiency of Fe₂O₃ was influenced by the presence Cl^- and SO₄^2-; however, 100% removal of As and Hg were achieved with both ZVI and Fe₃O₄, with no detectable influence of both anions. Iron oxide particles are being developed electrochemically as a barrier material for PRBs to allow for simultaneous As and Hg removal. The removal efficiency will be evaluated in column experiments and field-scale applications. In addition, the effects of several parameters, including the initial concentrations of As and Hg, the presence of cations and anions, pH, and dissolved oxygen, on the performance of iron oxide particles will be examined.