The preparation of activated carbon from apricot stone (ASAC) activated with H3PO4 and
its ability to remove the basic dye Congo red (CR) used in the textile industry in aqueous
solution are reported in this study. The FTIR spectroscopy is used to get information on
the interactions between the ASAC adsorbent and CR. A series of contact time experiments
were undertaken in stirred batch to assess the effect of the system variables. The results
showed that ASAC can be successfully used the wastewater treatment. A comparison of
two models on the overall adsorption rate showed that the kinetic of adsorption was better
described by the pseudo-second order model. The adsorption data of CR onto ASAC are
determined and correlated with common isotherms equations. The small values of the Root
Mean Square Error (RMSE) obtained for the Langmuir and Dubinin–Radushkevich models
indicate the best fitting of the curves. The monolayer adsorption capacity of CR is found to
be 32.85mg g−1 at 25 ◦C and 23.42mg g−1 at 65 ◦C at pH ∼ 13. The thermodynamic parameters
indicate a spontaneous and endothermic nature of the adsorption process. The positive
entropy (S◦) shows that the randomness increases at the solid–solution interface during
the CR adsorption, indicating that some structural exchange occurs among the active sites
of the adsorbent and CR molecules.