Optimization and application of acid-modified coal gasification fine slag for effective removal of chemical oxygen demand and volatile phenols in semi-coking wastewater

• The high removal efficiency for COD and volatile phenols in semi-coking wastewater was synthesized from coal gasification fine slag. • Enhanced porosity and active sites enable efficient pollutant removal. • The adsorption follows pseudo second order kinetics, indicating chemisorption dominance. • ACGFS offers stable, sustainable, and cost-effective wastewater treatment potential. The removal of chemical oxygen demand (COD) and volatile phenols (VP) from semi-coking wastewater is crucial for mitigating environmental pollution. This study investigates the acid modification of coal gasification fine slag (CGFS) using HCl to enhance its adsorption performance for COD and VP. Characterization via FTIR and XPS confirmed the enrichment of silanol (-SiOH) and hydroxyl (-OH) functional groups, which facilitate hydrogen bonding and electrostatic interactions with pollutants. The acid treatment significantly increased surface area from 332.84 m²/g to 573.44 m²/g and optimized micropore (0.07 cm³/g) and mesopore (0.34 cm³/g) structures, improving adsorption efficiency. Adsorption experiments demonstrated that ACGFS achieved 98.6 % COD removal and 99.2 % VP removal under optimized conditions of 20 % HCl concentration, 80-minute leaching time, and 50 °C leaching temperature. The adsorption capacities were 153.8 mg g −1 for COD and 14.4 mg g −1 for VP, following pseudo-second-order kinetics, confirming chemisorption as the dominant adsorption mechanism. VP adsorption was primarily influenced by micropore availability, while COD removal was governed by mesoporous structures and surface functional groups. The findings highlight ACGFS as a cost-effective and sustainable adsorbent for semi-coking wastewater treatment, offering a viable alternative to commercial activated carbon. Future research will focus on pilot-scale applications, multi-cycle reusability, and economic feasibility assessments to evaluate the practical implementation of ACGFS in industrial wastewater treatment.