Removal of dyes from aqueous solutions by straw based adsorbents: Batch and column studies

In this paper, the wheat straw materials have been simply modified by carboxymethylation to prepare a kind of new adsorbent. The adsorption of methylene blue (MB) from aqueous solutions onto modified straw has been studied. It was found that the adsorption capability of straw increased dramatically after modification. The investigation of pH effects indicated that the adsorbents had better adsorption performances in neutral and alkaline conditions. The adsorption isotherms were best fitted by the Langmuir equation while the adsorption kinetics was well described by both pseudo-second order equation and the Elovich equation. The adsorption behavior in a fixed-bed system followed Thomas model. It indicated that the adsorption behavior was a monolayer chemical adsorption and the rate-limiting step might be ion exchange reaction. Interestingly, after adsorption of MB, the disused adsorbents were not recovered for recycle as usual, but tried to remove another dye matter of methylene orange (MO) from aqueous solutions directly. It was proved that the MB loaded adsorbents were stable enough at pH > 6.0. and effective in the secondary adsorption of MO for altered surface structures of the straw based adsorbents after adsorption of MB. (C) 2011 Elsevier B.V. All rights reserved.