Effect of solution composition on the efficiency of Fe⁰ and lapillus permeable reactive barriers

The long-term behaviour of a permeable reactive barrier (PRB) composed of a granular mixture of zero-valent iron and lapillus for groundwater remediation of copper (Cu), nickel (Ni), and zinc (Zn) was studied through column tests. Solutions with or without calcium carbonate (CaCO 3 ) were used to evaluate the effect of groundwater geochemistry on the removal efficiency and hydraulic behaviour of the PRB. The performance of the granular mixture aged with an uncontaminated solution in the presence of CaCO 3 and subsequently permeated by Cu, Ni, and Zn was also studied. Finally, the removal efficiency using lapillus alone was evaluated. The results show that removal capacity was reduced by 68% for Cu, 54% for Ni, and 67% for Zn due to the presence of CaCO 3, highlighting the need to adapt the design of PRBs to specific geochemical conditions. The ageing of the granular mixture was instrumental in investigating the role of iron corrosion products in the removal processes. The removal efficiency of an aged mixture was reduced by 43% for Ni and 29% for Zn, remaining unchanged for Cu, suggesting that contaminant removal mainly occurs during iron corrosion. Finally, lapillus exhibited a strong affinity towards Cu and rapid exhaustion towards Ni and Zn.