Abstract Recently, the circular economy aiming at elimination of waste and the continual use of resources has attracted a lot of attentions. In the circular system, the resource recovery uses the recycled wastes as the raw material to manufacture new valuable products. This work focuses on a low-cost process, in which an activated carbon (AC) adsorbent was prepared from waste cation exchange resin by calcination and HNO3 activation hydrothermal method. Surface structure and chemistry of AC were characterized by SEM, XRD, FTIR and Boehm titration. It was found that the acid treatment could increase the number of pores and the content of oxygen-containing functional groups on AC surface. In the adsorption experiment, Methylene blue (MB) was used to assess the adsorption capacity of AC. Experimental results showed that the highest efficiency of MB removal was achieved by AC with modification of 4M HNO3, showing the acidification effect on the adsorption capacity of AC. Adsorption isotherms of Langmuir and Freundlich were employed to fit the experimental data. It was shown that MB adsorption on AC is more consistent with Langmuir model that assumes a homogeneous adsorption. In the adsorption kinetic analysis, the adsorption was found to follow the pseudo-second-order model, indicating that adsorption of MB on acidified AC is dominated by chemical adsorption. The study revealed that the waste ion-exchange resin is a proper precursor of carbon adsorbent for MB dye. This low-cost method would specifically reduce the environmental cost of waste disposal.

    Abstract
    1 Introduction
    2 Preparation of samples
        2.1 Activated carbon from resin
        2.2 HNO3-AC mixture
        2.3 Dye wastewater
    3 Results and discussions
        3.1 Surface structure and morphology of AC
        3.2 Characterization for chemical structure of AC
        3.3 Adsorption experiment
    4 Adsorption isotherm and kinetics
        4.1 Adsorption isotherms
        4.2 Kinetic of MB adsorption on AC
    5 Conclusion
    Acknowledgements 
    References

• Chane‑Yuan Yang(Department of Chemical and Materials Engineering, National Chin-Yi University of Technology)
• Chao‑Lang Kao(Department of Chemical and Materials Engineering, National Chin-Yi University of Technology)
• Pang‑Yu Hung(Department of Chemical and Materials Engineering, National Chin-Yi University of Technology)