The study deals with adsorption of Naphthol Green B on two unburned carbons and the parent coal, from which the UCs have been created in a fluidised-bed power station. Particular attention has been paid to the adsorption equilibrium modelling: experimental data has been analysed using 2-parameter (Langmuir, Freundlich) and 3-parameter (Redlich-Peterson) isotherms - both linear and non-linear regressions have been used for the estimation of the isotherm parameters. In the case of both UCs, the Langmuir isotherm model provides the worst fit, whereas 2-parameter Freundlich and 3-parameter Redlich-Peterson models are both good, from which 3-parameter Redlich-Peterson isotherm provides slightly better results (despite the penalty used for the higher number of parameters). In the case of both UCs, the linear regression of Freundlich and Redlich-Peterson models provides good results (comparable with non-linear regressions). Unlike both UCs, the best fit of the experimental data from the adsorption on the coal has been achieved by the Langmuir isotherm model. The results based on the Freundlich or Redlich-Peterson model were (in this case) somewhat worse. (C) 2016 The Chemical Industry and Engineering Society of China, and Chemical Industry Press. All rights reserved.