REMEDIATION OF ARSENIC AND MERCURY IN GROUNDWATER IN CHINA WITH IRON COMPOUNDS

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, applications of 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 & treat. PRBs are considered a particularly viable remedial technology in the areas of Yangtze River delta and Zhujiang River delta in the southern part of China, where clay underlies below the ground surface and presents a challenge for remediation.

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 iron compounds 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 by both anions. In addition, the effects of several parameters, including the initial concentrations of As and Hg, the size of iron compound particles, presence of cations and anions, pH, and dissolved oxygen, on the performance of iron compounds were examined. The remediation efficiency will be further evaluated in column experiments and pilot-scale tests.