In this work, the rate-limiting steps of reactive dye adsorption onto FS-400 activated carbon
were elucidated through the investigation of adsorption kinetics. These studies initially revealed
that only 20% of the available adsorption capacity was achieved during the first 6 h of mixing.
Kinetic profiles showed that the adsorption process was mainly controlled by external diffusion
during the first 30 min of the reaction, after which internal diffusion controlled the process.
The interruption test method identified the rate-limiting steps; the results showed that sorption
of reactive dyes onto FS-400 was mainly controlled by internal diffusion. Furthermore, the
external and internal diffusion coefficients and the desorption rate decreased after the
interruption period. The same parameters increased when the solution temperature was raised.
The thermodynamic parameters studied showed that the adsorption of reactive dyes onto
activated carbon was endothermic and is mainly controlled by internal diffusion with a minor
effect of external diffusion.
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