Electrokinetic Remediation of Copper-And Lead-Contaminated Loess Using Novel Hydrogel Electrodes Coupled with a Permeable Reactive Barrier Composed of Modified Activated Carbon and Carbon Fiber

Copper and lead contamination in loess areas poses a potential threat to soil environmental quality and sustainable land use, while the low permeability, high clay content, and strong buffering capacity of loess often limit the efficiency of conventional electrokinetic (EK) remediation. In this study, a modified activated carbon–carbon fiber (MAC–CF) composite reactive barrier was introduced into an EK remediation system to enhance the soil-phase depletion of Cu and Pb from contaminated loess. The effects of ordinary activated carbon (AC), MAC, CF, and different MAC–CF mixing ratios on current, cumulative electroosmotic flow (EOF), soil pH, electrical conductivity (EC), and potentially toxic metal (PTM) removal were systematically investigated. The conventional AC barrier increased system resistance and inhibited current transmission and EOF. The MAC barrier exhibited enhanced OH− adsorption and buffering capacity, decreasing the cathode-adjacent pH from approximately 9.8 to 8.8. CF incorporation improved barrier conductivity, increasing the peak current from 1.6 A for MAC (100%) to 4.0 A for MAC (25%) + CF (75%), while cumulative EOF increased from approximately 380 to 950 mL. The MAC (25%) + CF(75%) barrier provided the best balance between conductivity enhancement and cathodic alkalization regulation. Sectional Cu removal reached approximately 90% near the anode, whereas Pb removal ranged from approximately 18% to 29%, with a section-weighted mean of about 24.8%. The corresponding residual Pb concentrations (approximately 355–410 mg kg−1) indicate that the system is more effective for Cu and would require additional treatment to meet a conservative agricultural-soil target for Pb. The results support complementary functions of CF in maintaining conductive pathways and MAC in regulating cathodic alkalization. Because Cu and Pb in the spent barrier and electrolyte chambers were not quantified, the proposed precipitation-suppression and migration mechanisms are interpreted from the combined electrochemical, pH, EC, adsorption, and soil-residual evidence rather than from a complete metal mass balance.