Adsorption of binary mixtures of cationic dyes

Adsorption of cationic textile dyes namely, C.I. Basic Blue 41 and C.I. Basic Red 18 onto granular activated carbon (GAC) and silkworm pupa (SWP – a natural adsorbent) has been investigated for single and binary solute systems. Equilibrium isotherms were conducted for two, single solute systems and three binary combinations of the dyes. Although adsorption of C.I. Basic Red 18 on SWP showed no correlation with the Langmuir, Freundlich or Myers models, the Freundlich equation described the adsorption of Basic Blue 41 well and the Myers equation correlated reasonably well the two dyes on GAC. Of the multi-component models studied, the ideal adsorbed solution theory (IAST) gave reasonable predictions of the binary systems of the dyes on GAC but it failed to predict the binary system on SWP. The adsorption on SWP was shown to occur by chemisorption which was not affected by the presence of molecular oxygen.