Characterization of rare-earth Gd-doped iron–carbon materials and their effectiveness in treating waste leachate

Abstract

Gd/Fe–C composites were prepared by hydrothermal reaction and high-temperature sintering, and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) before and after strengthening with rare earth element Gd. The optimum process conditions for the treatment of waste leachate with Gd/Fe–C composites were also investigated, and the organic species in the mixed system were initially characterized by UV-vis analysis, molecular weight cut-off ultrafiltration analysis, and three-dimensional fluorescence spectroscopy to investigate the degradation patterns of organic species, molecular weight and functional groups. The results showed that the rare earth element Gd in the Gd/Fe–C material was mainly present in the form of Gd³⁺ and acted as a catalyst in the preparation of the material. The addition of the rare earth element Gd resulted in the appearance of elongated crystals in the material, a more detailed and compact material surface, the inhibition of the formation of Fe-based oxides, a significant increase in the amount of zero-valent iron and activated carbon, and the appearance of more active C–O and C–H functional groups. When the solution pH was 6, the temperature was 25 °C and the solid–liquid ratio between the Gd/Fe–C composite and waste leachate was 6 : 100; the degradation effect on waste leachate was most satisfactory, and the removal rates of COD, TOC and UV₂₅₄ were 70.54%, 56.13% and 95.27% respectively, and the removal rate of color was 97.37%. The main components of aged waste leachate are fulvic and humic acids. After treatment, most of the fulvic acid was degraded by the [H] and ˙OH produced by micro-electrolysis, which enhanced the biodegradability of the effluent.