Adsorption of Hexavalent Chromium from Aqeous Solution Onto Chemically Activated Ocimum Tenuiflorum Stem-A Kinetic, Linear Equilibrium and Thermodynamical Studies

Abstract

Low cost activated carbon from the stem of the plant Ocimum Tenuiflorum (OTA) was prepared by chemical activation method using sulfuric acid. The activated carbon was used for the removal of the Cr(VI) from waste water by batch process. Effect of initial pH, concentration of Cr(VI), amount of the adsorbent, contact time and temperature were studied. Activated carbon showed an excellent efficiency of removal of Cr(VI) from aqueous solution. Maximum adsorption capacity was found to be 95.9 mg g-1. pH studies on the adsorption revealed that low pH was favorable for the adsorption and optimum adsorption takes place at pH =1. Mechanism of the adsorption was studied and OTA followed interparticle diffusion at higher concentration of Cr(VI) and at lower concentration film diffusion contributes more towards the mechanism. Kinetic model of the adsorption shows that Pseudo second order kinetics was followed by the adsorption compared to pseudo first order or Elovich model which were studied. Linear and non linear adsorption isotherm was analyzed. Thermodynamic parameters calculation showed that ΔGo <0 for all the temperature and with increase in temperature the negative value increase indicating higher spontaneity at higher temperature. Interestingly both enthalpy of adsorption and entropy of adsorption was found to be positive for the adsorption. The activated carbon was characterized by FTIR and SEM.