In the present study, a systematic numerical study is conducted to investigate the mass transfer of a slightly contaminated spherical bubble under the effect of chemical reaction with the consideration of volume change of the bubble. The numerical approach is first validated by the benchmark tests, i.e., the dissolutions of a static bubble and a rising bubble. The numerical results are compared with the results from literatures and show very good agreements. Afterwards, the numerical method is utilized to study the chemical absorption process of a rising spherical CO2 bubble in the alkaline solution of NaOH. The shrinkage of the bubble and the decrease of bubble velocity during the chemical absorption process are taken into account, and the accumulation of the contamination on the bubble surface is also considered based on the stagnant cap model. The profiles of species concentration are presented in detail, and it can be found that the cap angle and the flow separation significantly influence the distribution of the concentration layers. The local mass transfer rate and reaction rate around the bubble surface are studied quantitatively, and the local mass transfer is found to be dominated by the chemical reaction directly. In additional, the supplement of the hydroxyl ion significantly affects the mass transfer which is mainly determined by the local velocity. (C) 2017 Elsevier Ltd. All rights reserved.