Tracking Cr(VI) removal with spectral induced polarization under ZVI and AC synergetic remediation

The structure and active components of the filling material play a critical role in the contamination remediation performance of permeable reactive barriers. However, current methods lack a comprehensive understanding of the structural evolution and long-term performance of these materials during remediation processes. This study utilizes column experiments combined with spectral induced polarization (SIP) monitoring to investigate the effectiveness of zero-valent iron (ZVI), activated carbon (AC), and their composite with sand in removing Cr(VI). Water chemistry, SEM-EDS and XPS methods were used to examine the structural changes and remediation efficacy of these reactive particles. The monitoring results show a notable synergistic effect between ZVI and AC particles, with the average removal rate of Cr(VI) by Sand + ZVI + AC (90.3%) being significantly higher than that of Sand + ZVI (36.2%) and Sand + AC (19.5%). This difference is also clearly reflected in the SIP spectral data, where the reduction in chargeability and scaled relaxation time when ZVI and AC are used together is approximately 2.4-4.3 times and 6.1 to 9.9 times that of using ZVI or AC alone. Changes in the ZVI matrix and the active surface area of particles, monitored through SIP parameters, exhibit a correlation with Cr(VI) removal rate, with chargeability being a particularly effective indicator. This research elucidates the relationship between SIP parameters and PRB remediation performance, highlighting the potential of SIP technology for monitoring and evaluating PRB remediation performance in Cr(VI) contamination.