Electrochemical injection for Ni-contaminated soil: potentials, electrodes, and chelants

The interaction between remediation and strengthening of heavy metal-contaminated soil remains unclear, necessitating further investigation into specific influencing factors. This study conducted model tests for the injected electrochemical strengthening and remediation of nickel (Ni)-contaminated soil. It adopted stepped and intermittent loading voltages, employed iron, graphite, and iridium–tantalum–titanium (ITT) as electrode materials, and used ethylene diamine tetraacetic acid (EDTA) and biopolymer as chelating agents. Various remediation and strengthening indices were evaluated, such as contaminant removal rate, drainage volume, shear strength, and energy consumption. The results showed that the injected electrochemical method significantly enhanced both the strengthening and remediation of contaminated soil with high water content. Compared with constant voltage loading, stepped and intermittent loading not only reduced energy consumption but also increased the overall heavy metal removal rate by 41.39% and 26.34%, respectively. Meanwhile, the shear strength of soil reached 65 kPa under stepped loading and 54 kPa under intermittent loading. Furthermore, the use of graphite and ITT electrodes prevented chelating agents from being consumed by iron ions, yielding further removal rate increases of 16.58% and 24.67%. The incorporation of sodium alginate mitigated heavy metal enrichment and increased the Ni2+ removal rate by 31.81% compared to traditional EDTA, thereby reducing the soil contamination from an unacceptable risk level to a possible one. These findings offer valuable insights for the injected electrochemical strengthening and remediation of contaminated soil.