Sorption-desorption isotherms of dyes from aqueous solutions and wastewaters with different sorbent meterials

The ability of activated carbon and different low-cost by-products and waste material as sorbents to remove
various reactive dyes from aqueous solutions and wastewaters was investigated. All aqueous dye solutions
contained 2,000 mg l-1 NaCl, to mimic real dye wastewater. Batch kinetic and isotherm experiments were
conducted to determine the sorption-desorption behavior of the examined dyes from aqueous solutions
and wastewaters by different sorbents, including activated carbon, fly ash, bentonite and bleaching earth.
The results from the aqueous solutions indicate that the form of the isotherm equation is not necessarily
unique for best description of both sorption and desorption data. The values of the isotherm
parameters are not the same, indicating a significant hysteresis effect.
Of the 9 sorption systems tested, 5 are best described by the Freundlich, 3 by the Langmuir and 1 by
the linear sorption model. Of the 7 desorption systems tested, 5 are best described by the Freundlich
and 2 by the linear model. In all cases, the sorption capacity for dye removal was higher for activated
carbon, followed by fly-ash and then by bentonite.