Modeling of binary and ternary batch adsorption systems via multidimensional logistic distribution and statistical physics

In many industrial sites, a series of various organic and inorganic co-contaminant species are simultaneously present in their aqueous discharges. This therefore justifies the recent interest and the choice of binary and ternary adsorption of three co-contaminant species to understand their competitive effects. Here we introduced two types of theoretical adsorption models, recently developed by us: multi-logistic distribution and statistical physics. These modeling approaches were applied in order to understand the adsorption of two cationic dyes (Rhodamine B, RB and Malachite Green, MG) and one metal cation (Cadmium Cd(II)) on granulated activated carbon (GAC). New experimental batch adsorption data were obtained with these mono-component, binary and ternary systems. The adsorption capacities of all these pollutants decreased from single to binary and ternary systems. Moreover, although Cd(II) did not lead to any notable competitive effect, when the two dyes were simultaneously present (binary and ternary systems) there was an increase in the adsorption capacity for RB and a decrease for MG, thus indicating a complex removal process due to different adsorption effects. Both models were used to calculate affinities, dissociation constants, steric and energetic parameters to characterize the single, binary, and ternary adsorption of tested pollutants. Modeling results indicated that the number of captured adsorbates per active receptor site of GAC decreased from single to binary and ternary systems, signaling a competitive effect for the same adsorption site. Based on this parameter, the adsorption orientation of these three pollutants was described. Interestingly, the models provided adsorption energies which allowed the characterization of the interactions between the adsorbates and the adsorbent surface. Calculated adsorption energies showed that the adsorption in single, binary, and ternary systems was associated to physisorption.