THERMODYNAMICS STUDY OF ADSORPTION OF WATER SOLUBLE DYESTUFFS ONTO PURIFIED PALYGORSKITE

Adsorption thermodynamics of catioriic pink FG,methylene blue and direct acid proof scarlet 4BS onto purified palygorskite were studied through static adsorption experiments, and the adsorption isotherms in the range of 298-328 K were determined. The results show that adsorption data of three water soluble dyestuffs onto purified palygorskite fitted well to the Langmuir isotherm. The adsorption of cationic pink FG and methylene blue onto purified palygorskite is an endothermic processes, and direct acid proof scarlet 4BS is exothermic in nature. The adsorption enthalpy changes, Gibbs free energy changes and entropy changes were calculated according to the relationship of the thermodynamic function. The adsorption enthalpy changes of cationic pink FG, methylene blue and direct acid proof scarlet 4BS are 0. 49, 0, 26 kJ/mol and 19. 68 kJ/mol respectively. The adsorption Gibbs free energy changes are in the range of -27. 48 -31. 21 kJ/mol. The negative of adsorption Gibbs free energy changes in all the cases are indicative of the spontaneous nature of the adsorption interaction, and the values of adsorption entropy changes are positive.