Adsorption of methylene blue on humic acid activated-carbon from weathered coal

Humic acid-activated carbon (HAAC) was prepared using weathered coal humic acid as the raw material, and its adsorption performance for methylene blue (MB) was systematically investigated. The results showed that pH, temperature, and the amount of adsorbent used had considerable effects on MB adsorption. Moreover, weathered coal HAAC demonstrated an adsorption capacity of 1039.8 mg/g at 298.15 K (pH = 3). When the addition amount of HAAC was 150 mg/L, the MB removal rate reached its highest of 99.41%. After repeating the adsorption and desorption experiments five times, the HAAC derived from weathered coal exhibited a remarkably high adsorption capacity for MB, approaching 850 mg/g. Kinetic analyses revealed that the adsorption rate of MB on HAAC derived from weathered coal is proportional to the square of the dye concentration. This quadratic dependence provides clear evidence that the process can be accurately described using a pseudo-second-order kinetic model. Finally, it was confirmed that humic acid derived from weathered coal can be converted into activated carbon for the purification of industrial wastewater, broadening its industrial applications. This study also realizes the diversified utilization of weathered coal.