High-efficiency removal of Cr(VI) in wastewater via coal gasification slag-based porous composite material

The safe and efficient treatment of Cr(VI)-containing industrial wastewater has attracted increasing attention, owing to its substantial potential hazards to both the ecosystem and humanity. A modified carbon-silicon porous composite material (MGFS) was prepared for efficient adsorption of Cr(VI) in wastewater in this study, using original coal gasification fine slag (GFS) - a typical solid waste as precursor material. It is demonstrated that the prepared porous composite material exhibited the richer pore structure, larger specific surface area, and more abundant functional groups compared with that of GFS. Under optimal conditions (adsorption time:150 min, pH: 3, temperature: 25°C, adsorbent dosage: 0.20 g), MGFS exhibited the highest Cr(VI) adsorption capacity of 4.94 mg/g with a removal rate of 98.85%, representing a 40.01% enhancement compared to GFS. Kinetic studies revealed that the adsorption process conforms to both the pseudo-second-order model and Ho-McKay model, indicating a multi-step rate-controlling mechanism. Equilibrium data was well-described by Langmuir isotherm models, suggesting a monolayer adsorption behavior. Thermodynamic analysis confirmed that the adsorption was a spontaneous exothermic process. The adsorption mechanism of Cr(VI) onto MGFS was systematically characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and other advanced analytical techniques. These findings not only provide theoretical support for the high-value utilization of coal gasification slag but also offer a viable strategy for heavy metal wastewater treatment.