[Adsorption kinetic mechanism of ionic soluble dye mixture on fly ash]

The fly ash from coal combustion was used as adsorbent for the removal of binary mixtures of dyes from aqueous solution. The binary solution included reactive red 23 and one of reactive blue 4, reactive yellow 4, acid black 1 and acid blue 193. The experimental findings show the removal efficiency of reactive red 23 is about 60% -70% while the removal of acid dyes exceeds 90%. The removal value of reactive blue 4 is about 85%, while the value is only 50% for reactive yellow 4. The adsorption kinetic data are good fitted with the pseudo-second-order kinetic model. The external diffusion coefficient solution is in the order of 10(-4) cm x s(-1), while the intraparticle diffusion coefficient is in the order of 10(-8) cm2 x s(1). Because all B(N) numbers are smaller than 100, adsorption of dyes on fly ash is mainly controlled by the external diffusion mechanism.