Electrokinetic remediation of chromium contaminated soil: Impact of particle size on treatment efficiency and bioavailability

• Soil undergoes substantial redox and pH changes during EKR. • Removal of Cr is effective in coarser particle size. • Metal speciation study aids to understand the mobility and bioavailability of Cr. • EKR alters the metal speciation of Cr and converts into more labile fractions. • Metal recovery is feasible by Hybrid-EKR technique. The electrokinetic remediation (EKR) is a potential method employed for removal and recovery of heavy metals from soil and various waste materials. However, it demonstrated promising efficacy in laboratory settings, diminished in practical implementations as a result of insufficient comprehension of in-situ conditions. In this study, experimental investigations were conducted to determine the effect of soil particle size on the performance of EKR. Four distinct soil particle sizes were utilized i.e., retained on 1.18 mm (EKR-A), 300 μm (EKR-B), 150 μm (EKR-C), and passing through 150 μm (EKR-D). The alteration in bioavailability as well as physiochemical properties of Chromium (Cr) was investigated through sequential extraction process (SEP) along with soil characterization techniques such as FE-SEM-EDX, XRD, FT-IR. Studies of soil particle size, composition and morphology indicate that as particle size decreases, pollutant concentration increases. Consensus was reached through the research that the treatment efficiency is substantially impacted by the particle size of the soil; in other words, smaller particle sizes led to diminished efficacy. The cumulative Cr removal percentages for EKR-A, EKR-B, EKR-C, and EKR-D were achieved as 27 %, 19 %, 10 %, and 7 %, respectively. The SEP study revealed that the initial soil Cr-concentration was predominated with oxidizable fraction (63–81 %) and the EKR facilitates the extraction of pollutants from the soil matrix by increasing their leachability from 1 % to 30 %, thus providing both removal and recovery of Cr as a feasible option.