Application of spectral induced polarization technique in monitoring zinc removal by activated carbon as a permeable reactive barrier material

Zinc accumulates in groundwater from mining operation and discarded batteries and poses a threat to environmental safety and human health. Activated carbon (AC), is an affordable media of permeable reactive barrier (PRB) for the in-situ zinc remediation. In this study, column breakthrough tests with spectral induced polarization technique monitoring, coupled with microscopic analyses, were utilized to investigate the zinc retention behaviors in activated carbon PRB. Chemical analysis indicated that Zn²⁺ retention on AC surface was primarily governed by cation exchange, electrostatic adsorption and precipitation. The quantity of Zn retention was well characterized by the real-time normalized chargeability derived from SIP signals. The Zn²⁺ migration simulation and characteristic polarizable units size revealed that the 0.01 μm pore throat channels impeded Zn²⁺ migration into internal pores at low Zn²⁺ inflow concentration due to restriction of overlapping electric double layer, which resulted in a reduction of effective adsorption area. This transport-limiting effect is alleviated at higher Zn²⁺ inflow concentrations due to EDL compression. Above results suggest the feasibility of the SIP technique in real-time monitoring of Zn remediation processes in a permeable reactive barrier set up.