Study on the adsorption isotherms of chromium (VI) by means of carbon nano tubes from aqueous solutions

Background: The presence of heavy metals in the environment especially in water supplies have caused many concerns because of their toxicity and non-degradability. Hexavalent Chromium (Cr) is one of the most toxic metals which is used in many industries, so it is essential to remove it from industrial wastewater. In this study, we made a comparison between different adsorption isotherms in the chromium (VI) removal process using carbon nano tubes from aqueous solutions. Methods: This experimental study used atomic absorption spectrophotometry. To determine the adsorption isotherms, a synthetic sample with defined concentration of Cr (VI) was prepared and different doses of adsorbent were added to it. The effect of initial Cr concentration, pH, adsorbent dose, and reaction time on removal of Cr was investigated. Temperature and mix rate were steady during a defined time. At the end, Cr (VI) concentration measured and adsorbents equality capacities were calculated via formulas and graphs. Data analysis were performed using descriptive statistics. Results: Adsorption capacities (qe) increased with increasing of initial Cr concentration, and reaction time decreased with increasing adsorbent dose and pH. Correlation coefficients for Langmuir, and Freundlich isotherms in oxidized Multi-Walled Carbon Nano Tubes (MWCNTs) were 0.93, 0.874, and 0.714 and in oxidized Single-Walled Carbon Nano Tubes (SWCNTs) were 0.904, 0.868, and 0.711 respectively. Conclusion: Chromium ions adsorption in carbon nano tubes is accordant to Langmuir isotherm model, and MWCNTs have more cc than SWCNTs. Carbon nano tubes are effective adsorbents in removal of Cr (VI) from aqueous solutions.