Tetracycline adsorption onto activated carbons produced by KOH activation of tyre pyrolysis char

• High surface area activated carbons were produced from tyre pyrolysis char.
• KOH activation allowed obtaining highly mesoporous activated carbons.
• These activated carbons are as good as commercial ones used in wastewater treatment.
• Kinetics and thermodynamic studies of tetracycline adsorption were performed.
• Activated carbons would improve the economic balance of pyrolysis oil production.

Tyre pyrolysis char (TPC), produced when manufacturing pyrolysis oil from waste tyre, was used as raw material to prepare activated carbons (ACs) by KOH activation. KOH to TPC weight ratios (W) between 0.5 and 6, and activation temperatures from 600 to 800 °C, were used. An increase in W resulted in a more efficient development of surface area, microporosity and mesoporosity. Thus, ACs derived from TPC (TPC-ACs) with specific surface areas up to 814 m2 g−1 were obtained. TPC, TPC-ACs and a commercial AC (CAC) were tested for removing Tetracycline (TC) in aqueous phase, and systematic adsorption studies, including equilibrium, kinetics and thermodynamic aspects, were performed. Kinetics was well described by the pseudo-first order model for TPC, and by a pseudo second-order kinetic model for ACs. TC adsorption equilibrium data were also fitted by different isotherm models: Langmuir, Freundlich, Sips, Dubinin–Radushkevich, Dubinin–Astokov, Temkin, Redlich–Peterson, Radke–Prausnitz and Toth. The thermodynamic study confirmed that TC adsorption onto TPC-ACs is a spontaneous process. TC adsorption data obtained in the present study were compared with those reported in the literature, and differences were explained in terms of textural properties and surface functionalities. TPC-ACs had similar performances to those of commercial ACs, and might significantly improve the economic balance of the production of pyrolysis oil from waste tyres.

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