Removal of three anionic orange-type dyes and Cr(VI) oxyanion from aqueous solutions onto strongly basic anion-exchange resin. The effect of single-component and competitive adsorption

Adsorption of three anionic Orange-type dyes (i.e., Methyl Orange, Orange II, Orange G) and divalent chromate oxyanion onto Amberlite((R)) IRN-78 from single- and bi-solute aqueous solutions have been investigated in view of testing the removal technologies for dye-contaminated wastewater. The research methodology was based on a combination of equilibrium adsorption, isothermal titration calorimetry, and C-13 CP MAS NMR studies. The adsorption followed the pathway of anion exchange between the pristine OH- ions and the oncoming anionic species. The supernatant solution thus became more alkaline, which, in some cases, gave rise to new dye species with an additionally ionized R-N-NH-R moiety, e.g., OII2- or even OG(3-). In the single-solute systems, the retention capacity of the resin towards various anionic solutes, on a per-mole basis, decreased in the following order: CrO42- > OG > OII approximate to MO. The retention of dyes was irreversible even in strongly alkaline media contrary to CrO42-, which was completely desorbed from the resin by a 1 mol L-1 NaOH solution. The competition between dye and chromate anions from their equimolar solutions mainly caused a marked decrease in the uptake of CrO42-, thereby pointing to preferential dye retention by Amberlite((R)) IRN-78. (C) 2016 Elsevier B.V. All rights reserved.