Restoration of alkaline soils contaminated by inorganic elements under pulsed electrokinetics

Electrokinetics (EK) offers a viable approach for extracting inorganic toxins from alkaline soils. Nevertheless, the progression of acidic and, peculiarly, the alkaline front in soil diminishes contaminant elimination efficacy by the precipitation of metal ions as insoluble hydroxides. Moreover, the so-called focusing phenomenon (driven by the convergence of pH fronts) weakens electric field strength within the soil, thereby hindering ionic mobility and making ions removal further time-intensive, raising reclamation costs through increased labor and electrical energy consumption, etc. To address these shortcomings of continuous electric field, we have investigated the effect of pulsed field (30 min ON/OFF cycles of 1 Vcm^-1) to slow down the production and propagation of pH fronts and thus delay the focusing development. Furthermore, Ethylenediaminetetraacetic acid (EDTA) was introduced at the anode to optimize the elimination and alteration of Cr⁶⁺ into Cr³⁺ ions by intense acidification. The findings indicate that pulsed fields have significantly enhanced the removal of ionic species by reducing the focusing localization and energy consumption. Additionally, EDTA effectively heightened the acidic environment, markedly improved the extraction of total Cr (74.4 %), facilitating accelerated Cr⁶⁺ reduction (89 %) and persuading the unfamiliar electroendosmosis trend that augmented anion transport. In contrast, a continuous field intensified the redox reaction, exacerbating the focusing zone at 30 hr of treatment and inhibiting ion removal, increasing energy consumption by 12.24 % relative to the pulsed strategy. In conclusion, pulsed field is a worthwhile alternative to the continuous approach, offering a controlled and energy-efficient process while minimizing anode deterioration and negative impacts on soil properties. Herein, it provides momentous insights for future field-scale applications, particularly in alkaline soils contaminated by heavy metals and salts, aiding the development of more cost-effective and environmentally sustainable soil remediation strategies.