Removal of chromium(VI) from aqueous solutions using mango leaf powder : Process optimization with Response Surface Methodology

Department of Chemical Engineering, National Institute of Technology Agartala, Agartala-799 046, Tripura, India Department of Civil Engineering, National Institute of Technology Agartala, Agartala-799 046, Tripura, India Department of Chemical Engineering, University of Calcutta, Kolkata-700 009, India E-mail : somanag.nita@gmail.com, abhijitju17@gmail.com, umishra123@rediffmail.com, drsudipkdas@vsnl.net Manuscript received 22 July 2016, accepted 26 August 2016 In the present work, a naturally available mango leaf, was investigated for removal of CrVI from aqueous solution. In a series of batch experiments, kinetics and equilibrium of sorption process were studied with respect to pH, initial CrVI concentration, adsorbent concentration, time, particle size and temperature. External mass transfer model and intra-particle diffusion models were used to predict the rate limiting step. Both had contribution in adsorption process but the internal diffusion was the rate controlling step. Numerical values of the coefficients indicated that the adsorption was quite fast. The kinetics was best described by pseudo second order model. Langmuir monolayer adsorption model was the best fitted one among the four isotherm models used. Sorption energy estimation by using Dubinin- Radushkevich model predicted the process was chemisorptions. The high temperature was found favourable, and the thermodynamic study suggested that the adsorption process was endothermic and spontaneous. A two-level two-factor full-factorial central composite design with the help of DESIGN EXPERT 7.0 statistical software, was used to optimize the process conditions for the maximum removal of CrVI from aqueous solution