Adsorption modeling via statistical physics theory allows to understand the adsorption mechanism of heavy metal ions. Therefore, this paper reports the analysis of the mechanism of copper ion (Cu2+) adsorption on four activated carbons using statistical physics models. These models contain parameters that were utilized to provide new insights into the possible adsorption mechanism at the molecular scale. In particular, a monolayer adsorption model was the best alternative to correlate the Cu2+ adsorption data at 25–55 °C and pH 5.5. Furthermore, the application of this model for copper adsorption data analysis showed that the removal of this heavy metal ion was a multi-cationic process. This theoretical finding indicated that Cu2+ ions interacted via one functional group of activated carbon surface during adsorption. In this direction, the adsorption energy was calculated thus showing that Cu2+ removal was endothermic and associated with physical interaction forces. Furthermore, these activated carbons showed saturation adsorption capacities from 54.6 to 87.0 mg/g for Cu2+ removal, and their performances outperformed other adsorbents available in the literature. Overall, these results provide new insights of the adsorption mechanism of this water pollutant using activated carbons