Studies on the optimum conditions using acid-washed zero-valent iron/aluminum mixtures in permeable reactive barriers for the removal of different heavy metal ions from wastewater

Abstract

The method of permeable reactive barriers (PRBs) is considered as one of the most practicable approaches in treating heavy metals contaminated surface and groundwater. The mixture of acid-washed zero-valent iron (ZVI) and zero-valent aluminum (ZVAl) as reactive medium in PRBs to treat heavy metal wastewater containing Cr(VI), Cd2+, Ni2+, Cu2+, and Zn2+ was investigated. The performance of column filled with the mixture of acid-washed ZVI and ZVAl was much better than the column filled with ZVI or ZVAl alone. At initial pH 5.4 and flow rates of 1.0mL/min, the time that the removal efficiencies of Cr(VI), Cd2+, Ni2+, Cu2+, and Zn2+ were all above 99.5% can keep about 300h using 80g/40g acid-washed ZVI/ZVAl when treating wastewater containing each heavy metal ions (Cr(VI), Cd2+, Ni2+, Cu2+, and Zn2+) concentration of 20.0mg/L. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to characterize ZVI/ZVAl before and after reaction and the reaction mechanism of the heavy metal ions with ZVI/ZVAl was discussed.