Background and purpose: Some problems such as filtration, centrifugation, and turbidity in effluent has limited the application of activated carbon and many nano-sized adsorbents. The magnetization of adsorbents using magnetic nano-crystals (MNCs) is a useful approach to overcome these problems. In the present study, magnetic activated carbon was synthesized (since it is separated fast and easily from solution) and employed as an adsorbent for removal of reactive dyes (Reactive black 5 (RB5) and Reactive red 120 (RR120)) from aqueous solutions.

Materials and methods: Physical, surface and magnetic properties of adsorbent were analyzed using XRD, SEM, TEM, EDX, VSM and BET techniques. The performance of adsorbent in removing dyes was investigated considering the effect of pH, contact time, adsorbent dose, initial dye concentration, and temperature in a batch system. The experimental data was analyzed by Langmuir, Freundlich and Temkin isotherms, pseudo-first and second order kinetic models, and thermodynamic equations.

Results: In our study, by increasing temperature and adsorbent dose and decreasing the initial concentration, at pH 3 and equilibrium time of 30 min the adsorption efficiency increased. The optimum dose of the adsorbent was 1 g/L. Based on the Langmuir isotherm model the maximum adsorption capacity of 192.6 and 188.7 mg/g was obtained for RB5 and RR120 dyes, respectively. The adsorption process of both dyes obeyed the Langmuir and pseudo-second order models. The thermodynamic results showed that the adsorption process of dyes was endothermic and spontaneous in nature.

Conclusion: The present study showed that the magnetic activated carbon in addition to features such as rapid and easy separation from solution, has a high potential for dye adsorption too.