Waste to Adsorbents: Porous Carbon Derivatives of Coal Gasification Fine Slag for Efficient Cr(VI) Adsorption in Wastewater

In this study, coal gasification fine slag was utilized as a raw material to develop a high-performance adsorbent through KOH activation, to assess its efficacy in removing Cr(VI) from heavy metal wastewater. The results revealed that the modified coal gasification slag that was prepared at a CGS-to-KOH mass ratio of 1:3 and a calcination temperature of 850 °C, exhibiting the most favorable characteristics, with a specific surface area of 1090.53 m²/g. The experiments demonstrated that the adsorption rate and adsorption amount of Cr(VI) surpassed 90% and 90 mg/g, respectively, at an initial Cr(VI) concentration of 100 mg/L under optimal conditions (pH of 2, adsorption temperature of 40 °C, adsorbent dosage of 1 g/L and an adsorption time of 180 min). The Characterization analyses confirmed that KOH activation facilitated the development of a hierarchical pore structure in coal gasification fine slag. Kinetic analyses demonstrated that the adsorption behavior adhered to a pseudo-second-order kinetic model (<i>R</i>² = 0.9903), highlighting chemical adsorption as the predominant mechanism. Moreover, the adsorption isotherms were better fitted by the Freundlich model (<i>R</i>² = 0.9588), indicating a multilayer adsorption process. This study presents a sustainable approach to the value-enhanced recycling of the bulk coal gasification solid waste and an effective remediation solution for Cr(VI)-contaminated wastewater.