Adsorption and reduction from modified polypyrrole enhance electrokinetic remediation of hexavalent chromium-contaminated soil

Abstract

Toxic metal pollutant Cr(VI) in the environment will pose a severe threat to animal and human health. In this work, Fe₃O₄@PPy, Arg@PPy, and Arg/Fe₃O₄@PPy were prepared to enhance adsorption of Cr(VI) by doping Fe₃O₄ nanoparticles and amino radicals into the original PPy structure. Their characteristics were investigated by FTIR, SEM, EDS, BET analysis, and batch adsorption experiments. And they were used as permeable reaction barriers (PRB) to combine with electrokinetic remediation (EKR) to remediate Cr-contaminated soil. Adsorption experiment results showed that the maximum adsorption capacities of PPy, Fe₃O₄@PPy, Arg@PPy, and Arg/Fe₃O₄@PPy for Cr(VI) were 60.43 mg/g, 67.12 mg/g, 159.86 mg/g, and 141.50 mg/g, respectively. They all followed the kinetic pseudo-second-order model and the Langmuir isothermal model with a monolayer adsorption behavior. In the EKR/PRB system, the presence of Fe₃O₄@PPy, Arg@PPy, and Arg/Fe₃O₄@PPy obtained the higher Cr(VI) removal efficiency near the anode than that of the PPy, increasing by 74.60%, 26.04%, and 68.64%, respectively. A strong electrostatic attraction between anion contaminants and protonated modified PPy and a reduction from Cr(VI) to Cr(III) appeared in the EKR remediation process under acid conditions. This study opened up a prospect for applying modified PPy composites to treat toxic metal-contaminated soil.

Keywords: Adsorption; Cr-contaminated soil; Electrokinetic remediation; Modified polypyrrole; Permeable reaction barrier; Reutilization.