Study On Adsorption Properties And Mechanisms Of Water Soluble Dyestuffs Onto Purified Palygorskite

Palygorskite is a chain-layer magnesium-aluminum silicate clay minerals. Since it was discovered in the 19th century, few attention has been paid on the adsorption mechanism of organic substances onto palygorskite.Adsorption thermodynamics and kinetics were carried out on adsorption properties and mechanisms of cationic pink FG, methylene blue and direct acid proof scarlet 4BS onto purified palygorskite which was prepared from Guanshan palygorskite clay.The results show that adsorption data of three water soluble dyestuffs onto purified palygorskite fitted well to the Langmuir isotherms; adsorption of cationic pink FG and methylenen blue were endothermic processes, but direct acid proof scarlet 4BS is exothermic in nature. The adsorption enthalpy changes of cationic pink FG, methylene blue and direct acid proof scarlet 4BS are 0.49,0.26 and -19.68kJ/mol respectively, adsorption Gibbs free enegy changes are in the range of -27.48—-31.21 kJ/mol. The negative of adsorption Gibbs free enegy changes in all the cases are indicative of the spontaneous nature,which show chemical sorption coexist with physical sorption. and the values of adsorption entropy changes are positive.Good correlation coefficients of methylene blue and 4BS were obtained for the pseudo-second order kinetics model. The apparent adsorption activation energy of adsorption is 13.92 and 11.91kJ/mol respectively. A relatively low apparent adsorption activation energy suggest that the adsorption dyestuffs may involve not only chemisorption but also physical adsorption process, which is likely due to its combined control of chemisorption and film diffusion.