Equilibrium, kinetic, and thermodynamic studies on the removal of Chromium (Ⅵ) using activated carbon prepared from Cocos nucifera roots as an adsorbent

摘要

Adsorption of Cr (Ⅵ) onto sulphuric acid activated Cocos nucifera roots was studied under batch mode. The effect of pH, temperature, contact time, adsorbent dosage, and initial Cr (Ⅵ) concentration was determined. Sorption of Cr (Ⅵ) onto activated coconut tree root carbon (ACTRC) was found efficient at pH of 2. The optimum adsorbent dose was found to be 2 (g/L) and the time taken to reach equilibrium was found to be 6 h. Toth isotherm was found to best describe the sorption mechanism among the five different isotherm models with R~2 of 0. 993. The maximum adsorption capacity as predicted from Langmuir isotherm was found to be 75 (mg/g). It was found from Dubinin-Radushkevich model that sorption of Cr (Ⅵ) onto ACTRC is physical in nature. Thermodynamic studies showed ΔH° value of-17. 416 KJ/mol indicating that the sorption process is exothermic and physical in nature. ΔG° and ΔS° values were found to be negative indicating that the sorption is feasible and spontaneous. Among the different kinetic models used for fitting the kinetic data, pseudo-first order model best describes the adsorption mechanism. A mathematical model for MB transported by molecular diffusion from the bulk of the solution to the surface of ACTRC was derived and the values of liquid phase diffusivity and external mass transfer coefficient were estimated.