Effect of mineral constituents on temperature-dependent structural characterization of carbon fractions in sewage sludge-derived biochar

The structure of carbon fractions and its characterization are critical for practical applications of the sewage sludge-derived biochar. However, the endogenous mineral constituents in sewage sludge can largely affect the structural characterization of carbon fractions in the obtained biochar. In this study, the high-mineral sludge biochar together with the biochar after acid washing was employed to explicate the effects of silicon- and aluminum-containing minerals on the structural characterization of carbon fractions. Results from Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) showed that major minerals such as kaolinite, metakaolin and quartz can obscure the presentation of functional groups and crystalline structure of carbon fractions. Peak deconvolution of Raman spectra demonstrated that both positions and peak area ratios of G and D bands were affected by the signals of aluminosilicates. Furthermore, aromatic rings developed and condensed with the increase in pyrolysis temperatures, leading to a gradual increase in structural ordering and the formation of turbostratic structures with poor crystalline and short-ranged orders. In addition, the effect of mineral constituents on physicochemical properties was related with pyrolysis temperature, which showed an enlargement in porosity at high temperatures (500-700 degrees C) but a more closely-packed powder mixture for low-temperature biochar (200-400 degrees C). From the interference of mineral constituents on temperature-dependent structure characterization of biochar carbon fractions, this study showed the necessity to explore interactions between mineral and carbon fractions to enhance potential application of high-mineral biochars. (C) 2017 Elsevier Ltd. All rights reserved.