Adsorption of anionic dye on natural and organophilic clays: effect of textile dyeing additives

The adsorption of Reactive Red 120 (RR120) onto natural and organophilic clays was investigated in aqueous solution in a batch system with respect to contact time, initial dye concentration, initial pH, and additives from textile dyeing industrial effluents. The results showed that the organophilic clay fixed more RR120 dye molecules than the natural clay when additives are not present. The adsorption kinetics was found to follow the pseudo-second-order model. Dye molecules formed a monolayer over the homogenous surface of the modified and unmodified adsorbent. When textile dyeing chemicals were added, the amount of dye adsorbed onto clay varied depending on the nature of the added chemical. However, on the overall, adsorption on the natural unmodified clay was enhanced, whereas it remained reduced or at least unchanged in case of the organophilic clay. Adsorption on both clays was enhanced when all additives were present together. Adsorption was also enhanced when non-clay minerals (>2 mu m fraction) were present in the unmodified bulk clay sample. Fourier transform infrared spectroscopy analyses showed strong evidence of interactions between RR120 dye and clay and also with additives.