Enhanced remediation of Pb(II)-Contaminated Fine-Grained soil using citric acid ex situ leaching coupled with electrochemical treatment

This study proposes an efficient ex situ remediation method combining leaching with electrochemical treatment for Pb(II)-contaminated fine-grained soil. During the leaching stage, citric acid (CA) was identified as the optimal leaching agent, with the optimal washing conditions determined as: 0.1 mol/L CA (pH 3), liquid-to-solid ratio of 10, and a duration of 3 h. Under these conditions, the Pb(II) removal rate of 17.21% was achieved. Crucially, electrochemical enhancement was implemented during the filtration phase using a custom-designed vertical apparatus operated under constant current mode (2-4 mA/cm²), significantly improving remediation efficacy. Orthogonal experiments revealed current density as the dominant factor influencing Pb(II) removal. The optimal parameters (P₃T₂₀I₃) were: pressure of 0.57 MPa, electric field initiation at 20% before the filtration-threshold time point (36 min), and current density of 3 mA/cm². This integrated approach achieved a remarkable Pb(II) removal rate of 70.1% within 3 h, representing a fourfold increase compared to single-stage leaching. Morphological analysis of Pb(II) in soil samples post leaching and electrochemical remediation, conducted using the BCR sequential extraction method, revealed that the Pb(II) fractions removed in the regions near both the cathode and anode were predominantly in the exchangeable (F1) and reducible (F2) states, with a smaller proportion in the oxidizable (F3) state. This indicates that the remediation treatment successfully reduced the mobility and bioavailability of the heavy metal, thereby diminishing its environmental impact. This combined remediation technology offers advantages of short duration and operational simplicity, enabling the deep removal of pollutants exceeding environmental standards in soil.