Elimination of Cr(VI) from chromium slag with poplar lignin by electrochemical treatment in sulfuric acid solution.

In this paper, we proposed a novel method to eliminate nocuous Cr(VI) from chromium slag with poplar lignin by electrochemical treatment in sulfuric acid solution. In this electrochemical process, self-made Ti/SnO-Sb anode and graphite cathode were applied, and the oxidative degradation of lignin proceeded simultaneously with the reduction of Cr(VI) in one pot. The influences of pivotal factors on electrocatalytic redox efficiency were investigated, such as chromium slag concentration, lignin concentration, current density, sulfuric acid concentration, and reaction time. The results showed that the elimination rate of Cr(VI) in chromium slag was 97.16 ± 1.13% and the total yield of lignin degradation products reached 93.78 g/kg lignin under the optimal conditions. X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDS), and UV-visible spectrophotometer studies confirmed that most of the Cr(VI) ions were reduced to Cr(III) ions with the aid of lignin, and a small amount of Cr(VI) ions were adsorbed by lignin residue. Importantly, this method provides a typical example of "waste control by waste", which is treating waste chromium slag with waste lignin that can be an effective way to eliminate Cr(VI).