RESUMO
The purpose of this study was to examine the combination of magnetic anion-exchange microbeads (MAM) and magnetic cation-exchange microbeads (MCM) to remove crystal violet (CV; a basic dye) and acid green 9 (AG9; an acidic dye) from their individual and combined solutions. Adsorption kinetics and isotherms experiments were performed in batch mode. CV and AG9 displayed superior affinity towards MCM and MAM, respectively, and their combined solution was efficiently adsorbed by combining MCM and MAM. The pseudo-first-order, pseudo-second-order, Elovich and intra-particle diffusion models well described the adsorption kinetic data, and the pseudo-second-order model appeared a better fit for the two-component CV/AG9 system. The better fit of the Langmuir isotherm for CV adsorption indicated that CV adsorption occurred on active sites with equal affinity in the monolayer. In contrast, AG9 adsorption onto the heterogeneous MAM surface appeared to be multilayered adsorption. The adsorption capacities of the two dyes decreased with the increase in the co-existing salt concentration and increased only slightly at the high salt level due to the salting-out effect. Moreover, these microbeads maintained most of their initial capacity during five reuse cycles, indicating the great potential of MCM and MAM to remove basic and acidic dyes in practical applications.