Adsorption Behavior of Methyl Orange onto Modified Ultrafine Coal Powder

The adsorption of methyl orange onto ultrafine coal powder (UCP) and modified ultrafine coal powder (MUCP) from aqueous solutions were studied, in which the influence of contact time, dosage, temperature, pH, and methyl orange concentration in the solution were investigated. The adsorption kinetics of methyl orange by UCP and MUCP can be described by the Lagergren first-order and pseudo second-order kinetic models, respectively. The adsorption isotherms of methyl orange onto MUCP at 303, 313 and 323 K follow the Freundlich and Langmuir isotherm equation. Values of ΔG0 for methyl orange adsorption onto MUCP are −22.55, −23.10 and −23.79 kJ·mol−1 at 303, 313, and 323 K, respectively. The values of ΔH0 and ΔS0 are −3.74 kJ·mol−1 and 61.99 J·mol−1, respectively. The adsorption process is spontaneous and exothermic.