Modeling binary adsorption of hexavalent chromium and Xylidine Ponceau dye onto an agave-polymer composite in batch...

Hexavalent chromium and Xylidine Ponceau dye form a binary mixture that is highly hazardous to the environment. The presence of a second pollutant modifies the adsorbent performance towards one or both pollutants, either by synergism or antagonism. This work evaluated the adsorption performance of a chitosan-based adsorbent over a binary mixture of Cr(VI) and Xylidine Ponceau in batch and fixed-bed configurations. The predicted binary isotherm accurately displayed how the adsorption capacity was affected by the concentration of the other pollutant, based on mono-component and binary adsorption data. The Cr(VI) adsorption capacity remained almost unaffected (~ 13.6 mg/g) by the presence of Xylidine Ponceau dye. However, Xylidine Ponceau adsorption capacity was significantly affected by chromium due to the selectivity towards this pollutant, decreasing from 26.9 to 11.4 mg/g. The kinetics of Xylidine Ponceau adsorption became faster in the presence of chromium, with PFO kinetic constant going from 0.0270 to 0.1148 1/min, suggesting interactions between both species. The breakthrough curve analysis evidenced a large mass transfer zone, indicating high mass transfer resistance. In this system, the used bed fraction was 46%; within this fraction, chromium occupied 31% of the surface, while the dye covered 13%, as accurately estimated by the modified Thomas model.