ABSTRACT Atrazine is an herbicide used to remove weeds in agricultural crops; however, because it is considered toxic, options for removing it from the environment are needed. Adsorption on biochar is an efficient technique for removing organic contaminants. In this study, the atrazine adsorption capacities of two biochars (BCA400 and BCA700) produced from rice husks at different pyrolysis temperatures (400 and 700 °C) were compared by phenomenological modeling. The biochars were characterized by SEM, FTIR and BET. Experimental kinetic and equilibrium data were obtained to evaluate Langmuir, Freundlich and BET isotherms and to conduct intraparticle diffusion. In comparison to BCA400, BCA700 showed a higher adsorption capacity at a higher pyrolysis temperature, and the Freundlich isotherm best described its system. To describe the kinetic adsorption data for the biochars, a phenomenological model based on intraparticle diffusion was applied, and the model fit well to these data for each biochar. This model is slow and involves the transport of atrazine to the pores of the biochar. Thus, the predictive model can be scaled up to adsorption systems.