A thermodynamic study of the adsorption of organic dyes on palygorskite clay

The adsorption isotherms of such organic dyes as methylene blue,crystal violet and aniline blue in water on palygorskite based on the purification of Jingyuan palygorskite clay were studied through static adsorption experiments,with a discussion on the thermodynamic characteristics. The results show that the equilibrium of the three kinds of dyes can be reached in about 30 minutes in the range of experiment temperatures,the adsorption isotherms of these three dyes on purified palygorskite fit Langmuir model fairly well,and the saturated adsorption capacities from Langmuir models are in order of crystal violetmethylene blueaniline blue. The adsorptions of the three dyes are all endothermic processes,the adsorption enthalpies of methylene blue,crystal violet and aniline blue are 15.52,9.26 and 2.59 kJ/mol,respectively; the adsorption Gibbs functions vary in the range of -35～-30 kJ/mol and the adsorption entropies are all positive values. The adsorption processes are spontaneous.