Transport modeling of ZVI-AC mixtures in Cr(VI) remediation driven by spectral induced polarization

Cr(VI) remediation performance of zero valent iron (ZVI) and activated carbon (AC) mixtures is investigated via Spectral Induced Polarization (SIP) and transport modeling in two parallel laboratory columns. The strong correlation (R² = 0.75-0.96) between chargeability and Cr (VI) removal capacity provides a real-time proxy for tracking reactive surface area dynamics and contaminant degradation progress. Acid-washed ZVI demonstrates enhanced reactivity, with prolonged remediation efficiency. Reactive transport modeling calibrated by chargeability improves accuracy of contaminant breakthrough curves, revealing distinct removal capacities and material utilization efficiencies in different zones of the two laboratory columns. In the acid-washed column, the lower section of the column shows higher Cr(VI) removal (3.92 mg/g) and lower active surface area depletion rate (0.012 g/mg) than the upper section, highlighting the early confrontation of the Cr(VI) plume with ZVI-AC mixtures in the lower section. SIP reveals the spatial heterogeneity for Cr(VI) removal capacity of ZVI-AC, facilitating the zoned optimization of PRB design to extend the barrier's service life.