In this study, we found the raw coal fly ash (CFA) that had not been subjected to any pretreatment process had superior adsorbing ability for the anionic dye Acid Red 1 (AR1) than did two modified coal fly ashes (CFA-600 and CFA-NaOH). The adsorption capacities followed the order CIA > CFA-600 > CFA-NaOH, and they each increased upon increasing the temperature (60 degrees C > 45 degrees C > 30 degrees C). The adsorptions of AR1 onto CFA, CFA-600, and CFA-NaOH all followed pseudo-second-order kinetics. The isotherms for the adsorption of AR1 onto the raw and modified coal fly ashes fit the Langmuir isotherm quite well; the adsorption capacities of CFA, CFA-600, and CFA-NaOH for AR1 were 92.59-103.09, 32.79-52.63, and 12.66-25.12 mg g(-1), respectively. According to the positive values of Delta H degrees and Delta S degrees, these adsorptions were endothermic processes. The ARE and EABS error function methods provided the best parameters for the Langmuir isotherms and pseudo-second-order equations, respectively, in the AR1-CFA adsorption system. (C) 2008 Elsevier Ltd. All rights reserved.