Adsorption studies of Toluidine Blue from aqueous solutions onto gypsum

Gypsum was investigated as an inexpensive and efficient adsorbent to remove Toluidine Blue from aqueous solution. The adsorption studies were carried out at room temperature. Batch mode experiments were conducted at 25 degrees C to study the effects of pH and initial concentration of Toluidine Blue. The adsorption data was analyzed by using the Langmuir, Freundlich and Tempkin isotherm models and was found to give better results with respect to Langmuir equation. The maximum monolayer adsorption capacity was found to be 28 mg of the dye per gram of gypsum. The data were also studied in terms of their kinetic behavior and was found to obey the pseudo second order equation. (C) 2008 Elsevier B.V. All rights reserved.