Recovery of the Dye Intermediate DNDS from Aqueous Solution by Adsorption onto Resins

Abstract

Four kinds of resins were investigated for the recovery of 4,4‘-dinitrostilbene-2,2’-disulphonic acid (DNDS), which is present as a pollutant in wastewater, and their adsorption behaviour and mechanisms assessed. One of the resins, YWB-38, exhibited much better adsorption properties towards DNDS than the other two commercial acrylic ester resins XAD-7 and HP2MG. The Langmuir and Freundlich adsorption models were fitted to the experimental equilibrium data when the Langmuir model was found to provide a better fit for all resins over the temperature range studied. The investigation indicates that hydrophobic interaction provides the main mechanism in the adsorption of DNDS onto XAD-4 resin and that such interaction decreases significantly when additional methanol (10%) is added to the DNDS solutions. While the main interaction between the acrylic ester resin and adsorbate is hydrogen bonding, this can be enhanced to some extent by increasing acid concentration. Adsorption dynamics, column adsorption and desorption processes were also investigated to explore the differences in adsorption behaviour and mechanism on the polystyrene resin XAD-4 and acrylic ester resins.