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Background and purpose: Nitrate is one of the most common chemical pollutants in groundwater in the world. Adsorption has been considered as an effective and efficient method of removing pollutants, particularly nitrate from aqueous solutions and so the aim of this study was to magnetization of the carbon nanotubes with zero-valent iron and using it as an adsorbent for the removal of nitrate from aquatic environments. Materials and methods: In this study, reduction method for converting divalent iron into zero-valent iron and co-precipitation method for iron particles deposition on carbon nanotubes was used. Characteristics of absorbent were analyzed by SEM (structural equation modelling), XRD (X-ray powder diffraction), and VSM (value stream mapping) techniques. In this study, the effect of the pH, contact time, mixer speed, temperature, adsorbent dosage and the concentration of nitrate was investigated by one factor at the time method and then was optimized. Results: The pH equal to 3, 60 min contact time, 200 rpm stirring speed and 1 g/l absorbent was obtained as the optimum conditions in the adsorption of nitrate. Investigating the isothermandkinetic models showed that the experimental data correlate to the Langmuir adsorption isotherm model (R2 > 0.997) and pseudo-second order kinetic (R2 > 0.993). The reaction thermodynamic study also expressed endothermic and spontaneous reaction. Conclusion: In optimal conditions, carbon nanotubes modified by zero-valent iron has well potential to quickly and effectively remove nitrate and simply be separated from the solution by the magnet due to its magnetic property.

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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.