An increasing Cr recovery from soil with catholyte-enhanced electrokinetic remediation: Effects on voltage redistribution throughout soil sections

Abstract

The evolution of potential gradient across different soil sections that were responsible for divergence of Cr migration in electrokinetic (EK) remediation need further investigate. Here, the redistribution of Cr and voltage was conducted out under four kinds of catholytes applying a constant potential. The results showed that the total removal efficiency of dissolved Cr from soil matrix achieved 51.7% with humic acid (HA) catholyte, compared to 40.4, 36.5 and 31.9% with KCl, citric aicd (CA) and H2O catholytes, respectively. The voltage drops on soil cells were enhanced with assisted catholytes, in which facilitating the migration capacity of Cr out of soil in a faster way. The voltage shifted to cathode electrode with a significant value of above 17 V over 12 d due to polarization in EK-H2O, which may become the limiting factor for driving the Cr migration. The voltage located in the last two soil slices that controlled by electric conductivity of pore water made a large proportion of 4.3–5.2 V (1.08–1.4 V cm−1) in EK-CA, which was consistent with the highest Cr removal efficiency of 64.3–85.6%. Whilst the voltage concentrated in the first soil slice and central slices related to water holding capacity reached 3.3–5.6 V (0.83–1.40 V cm−1) in EK-HA, contributing to a remarkably increasing Cr removal efficiency of 49.3–58.7%. In addition, HA can restrain the transformation and migration of Ca and S ions. Furthermore, higher migration potential for Cr indicated the voltage were efficiently consumed on Cr depletion in EK-HA. These suggested that HA was optional catholyte for site with the utmost Cr recovery and lower energy loss.