Quantitative assessment of residual carbon content and oxidative shrinkage behavior of coal gasification slag through in situ high-temperature stage microscope

Separation of residual carbon from inorganic components has been recognized as an essential strategy for the high-value utilization of coal gasification slag (CGS), while limited studies were conducted to directly examine the distribution of the residual carbon in CGS. In this study, CGS was pretreated by being wet-sieved, acid-washed or ashed, and the shrinkage behavior of the above samples during the oxidation process were studied through in situ high-temperature stage microscope. The results indicated that the carbon-containing CGS predominantly exhibited a carbon framework and fine-sized ash particles were wrapped or nested within the pores of carbon particles. The shrinkage of the samples within the temperature range of 550–650 °C was mainly associated with the oxidation of the residual carbon. Therefore, the residual carbon content in CGS could be quantitatively assessed according to the shrinkage behavior. A nonlinear correlation between the shrinkage rate of CGS and the residual carbon content across the full particle size range was established and the reliability of the derived fitting formula was validated. In addition, the shrinkage of CGS within the temperature range of 750–900 °C was associated with the bonding interactions between residual C=O and O=C-O functional groups and metallic bonds. This research can evaluate the separability by directly investigating the distribution of residual carbon in CGS, which provides important guidance for the effective separation of carbon and ash in CGS.