Kinetics, thermodynamics and isotherm studies of malachite green adsorption by modified orange peel

Kinetics, thermodynamics and isotherm studies o f malachite green (MG) adsorption by orange peel (OP) modified w i t h ethanol, calcium chloride and sodium hydroxide were performed. E f f e c ts o f i n iti a l dye c o n c e n tr a ti o n , t e m p e r at u r e a n d p H o n the a d s orp ti o n w e r e studied at the different c o n tact t i m es . T h e a m ou n ts o f MG adsorb ed onto OP increased w ith increasing c o n tact t i m e, i n itial d y e c on c e n trati o n , s o l u ti o n t e m p e r a t ur e, and pH . M a x i m u m dye adsorption w as about 92.90 % u n d e r all the e x p e r i m e n tal c o n d iti o ns . Percent desorption of MG from the surface of OP was lower in the alkali and HCl solutions and higher in an acetone-water mixture of 50%. Adsorption kinetics was best fit the pseudo-second order model with correlation coefficients of 0.99 and 1 for the concentrations studied. Thermodynamic results indicated a spontaneous adsorption. A d s orp ti o n i s o t h e r m obeyed t h e La n g m u ir m od el. The Langmuir adsorption capacity was determined as 14.55 mg g -1 . FT-IR and SEM analyses were also recorded before and after the adsorption.