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A carbonaceous adsorbent prepared from hulls of Vitex doniana by H3PO4 treatment was investigated for its efficiency in methylene blue (MB) adsorption in aqueous solution. The characterizations of materials are carried out by Fourier Transform Infrared Spectroscopy (FTIR), pH (6.2) and the iodine index measurement which showed that our powder activated carbon is primarily made up of meso and macro pores. The influence of major parameters governing the efficiency of the process such as, solution pH, sorbent dose, initial concentration, ionic strength and contact time on the removal process was explored. The Time of balance of adsorption is obtained to 40 minutes. The output of elimination of the molecules of the MB to this balance is to 85.92%. The variation of pH showed that the maximum of adsorption of the MB is with pH=10. Four theoretical adsorption isotherms namely Langmuir, Freundlich, Temkin and Dubinin -Radushkevic were used to describe the experimental results. The models of Temkin and Dubinin- Radushkevic describe better the adsorption of the methylene blue.
The reaction of adsorption of this dye is endothermic and the mechanism of adsorption is chemical. The pseudo-first order kinetic models, pseudo second order, Elovich and intra particulate have been applied to the experimental data and that which is appropriate is the kinetic model of pseudo second order.