Integrated lignin-mediated adsorption-release process and electrochemical reduction for the removal of trace Cr(vi)

Abstract

Hexavalent chromium Cr(VI) is extremely toxic and is classified as a human carcinogen, even at trace concentrations. Hence, it is critical to develop reliable and efficacious methods for its elimination. Here we report on the development of an effective lignin-mediated adsorption-release process based upon the pH-dependent solubility of lignin to significantly enhance the electrochemical removal of trace Cr(VI). The adsorption and pre-concentration of Cr(VI) was carried out at pH 2.0, while the release and electrochemical reduction was performed at pH 11.0. The 100% efficient release process was due to the complete dissolution of lignin within alkaline solution. The released Cr(VI) ions were electrochemically reduced, forming insoluble Cr(OH)₃, which could be easily separated. This novel approach overcomes the drawback of non-degradability in adsorption by the latter electrochemical reduction phase and the efficiency limitation of electrochemical process by the prior preconcentration step. The new integrated lignin-mediated adsorption-release and electrochemical reduction process proposed in this study comprises a promising strategy for the removal of trace concentrations of Cr(VI).