The preparation of coal-based carbon materials traditionally uses anthracite as the carbon source. In the present study, two types of porous carbon materials were prepared, one by tube furnace heating (CM1) and one by microwave processing (CM2), through the KOH activation method using the residue (YNC1) from the oxidative degradation of lignite. The structure-function relationships of the obtained materials were explored by studying the dynamic law and mechanism of methyl orange adsorption. Results showed that both CM1 and CM2 contained aromatic and hydroxyl (secondary alcohol) moieties but no carboxyl groups, ketone groups or long-chain aliphatic hydrocarbons. Both materials were dominated by micropores and mesopores, with a greater proportion of micropores than mesopores. The micropore content was higher in CM2 than in CM1. Additionally, structural characterisation revealed that the microwave-based KOH activation could open aromatic structures. Studies on the adsorption of methyl orange by the carbon materials indicated that the secondary hydroxyl groups on the surface of the carbon materials were active sites for chemical adsorption and played the key role in adsorption, leading to monolayer chemical adsorption. Furthermore, the distribution pattern of hydroxyl groups produced by the polarity selection of the microwave field was more favourable for chemical adsorption. The dynamic law of CM1 and CM2 adsorption of methyl orange conformed to the quasi-second-order kinetic model. The adsorption process comprised two stages: external surface adsorption, followed by the diffusion of methyl orange in pores.