Graphene-Alginate Fluids as Unconventional Electrodes for the Electrokinetic Remediation of Cr(VI)

Electrokinetic remediation of groundwater pollutants uses electrical fields to draw contaminants towards electrodes, where they are removed through diverse mechanisms. Conventional electrodes are installed in discrete positions in the soil. Here, we develop unconventional electrodes for the electrokinetic remediation of Cr(VI). Our electrodes are fluids comprised of sodium alginate and graphene particles in aqueous solution and can therefore be injected in the location of interest to facilitate their installation. The subsequent injection of CaCl2 solutions induces gelation (as demonstrated by shear rheology), forming a conductive material (as demonstrated by voltammetry experiments). This material sorbed Cr(VI), as demonstrated in sorption experiments conducted under no-flow conditions and even without any applied electric potential. Therefore, it could be placed downstream of the pollutant to act as a barrier, controlling Cr(VI) migration and providing protection for human or ecological receptors. In a saturated model sandy aquifer, Cr(VI) was drawn towards our unconventional electrode barrier using a 12 V differential voltage, thereby decreasing its concentrations by approximately 70% in 30 min (starting from 0.35 mM Cr(VI), as demonstrated using a spectrophotometer). The net reduction of Cr(VI) concentrations in water was achieved without its extraction from the electrode proximity, because our graphene-alginate electrodes sorbed Cr(VI). Our findings provide a proof of concept of a novel remediation approach, which combines electrokinetic remediation with injectable barriers.