Iron-carbon composite as flow electrode active material for highly efficient electrosorption of uranium from radioactive wastewater

A kind of iron-carbon composite for efficient electrosorption of uranium from radioactive wastewater was prepared by simply carbonization of cellulose and ferric nitrate, and the uranium electrosorption performance and behavior of the iron-carbon composite as flow electrode active material were investigated for low-concentration (below 50 mg/L) uranium-containing wastewater. By regulating the experimental conditions such as cellulose particle sizes, the mass ratio of cellulose/Fe(NO3)3, liquid flow rate, pH, and electric field strength, it was found that under the optimized conditions, the uranium removal ratios were 66.8, 81.92, 95.2, and 97.75 % for initial concentrations of 0.1, 0.5, 5.0, and 50.0 mg/L, respectively. The uranium concentration could be reduced from 0.1 mg/L to 0.0332 mg/L (the emission standard is 0.05 mg/L in China, GB 8798–1996) within 180 min of treatment. In addition, the material maintained an average salt removal rate of 26.27 μg cm−2 min−1 after 36 cycles of electrosorption. It achieved a uranium removal ratio of 87 %, and the upper limit of the electrosorption capacity was still not reached. Combined with X-ray photoelectron spectroscopy (XPS) analysis, the results indicated that the uranyl ion (UO22+) was firstly adsorbed on the surface of the active material after entering the flow electrode. Then, parts of the UO22+(Ⅵ) were reduced to uranium dioxide [UO2(Ⅳ)] under the synergistic action of zero-valent iron (ZVI) and cathodic electro-reduction and were finally immobilized on the electrode surface. This study proposed an innovative application of iron-carbon composite as flow electrode active material in FCDI for the treatment of uranium-containing wastewater with low-concentration (below 50 mg/L).