Evaluation of the High Metals-Containing Coal Gasification Fine Slag as a High-Performance Adsorbent for Malachite Green Adsorption

The concept of treating waste with waste is of great significance to realize the sustainable development of human society. In this work, the high metals-containing coal gasification fine slag (CGFS) from the coal gasification industry is directly transformed into an excellent adsorbent for malachite green wastewater adsorption. CGFS exhibits a rough and porous structure, which is mainly composed of SiO2 and various metal compounds. Numerous spherical structures which are generated by the melting of inorganic substances are distributed on the surface of CGFS with a large number of flocculent carbon structures covering the substrate or interspersed. Experiments confirm that CGFS is a competitive adsorbent for the removal of malachite green due to its low cost and high adsorption performance. The theoretical maximum adsorption capacity of CGFS at 298 K predicted by the Langmuir model reached as high as 1787 mg/g and the capacity increases with the temperature. The removal efficiency reached 100% for CGFS at a solid–liquid ratio of 0.05 g/100 mL and a malachite green concentration of 100 mg/L. A dominant role of chemisorption was confirmed by the analytical results of the pseudo-second-order model and the Freundlich model combined with the characterization results. The metal oxides and carbon structures in CGFS are presumed to be the main active adsorption sites. From the fitting of the intraparticle diffusion model, the adsorption rate was limited first by membrane diffusion and then by intraparticle diffusion as the adsorption process proceeded.Graphical Abstract