LAUSR

This paper aims to evaluate the simultaneous adsorption of basic red 2 (BR2) and basic violet 3 (BV3) in a binary system in a batch mode using date stones as low cost adsorbents. For both dyes, experimental kinetic data were well fitted by the Brouers–Sotolongo model (R2 = 0.99) and intraparticle diffusion was the controlling step in mass transfer mechanisms. The intraparticle diffusion extent was found to be lower for BR2 (1.13×10−11 cm2/s) than for BV3 (1.11×10−11 cm2/s) when compared to individual solutions (1.24×10−10 cm2/s and 1.76×10−11 cm2/s for BR2 and BV3, respectively). The equilibrium study revealed lower adsorption capacities (41.95 and 88.91 mg/g for BR2 and BV3, respectively) compared to the individual sorption results (92.00 and 136.00 mg/g for BR2 and BV3, respectively) for both dyes. To assess the extent of competition and the preference of dyes for functional sites, competition and separation factors were calculated suggesting an antagonistic effect as well as a greater affinity for BV3 than for BR2 to the adsorption sites. The equilibrium adsorption results were best fitted by modified Langmuir and P-factor Langmuir isotherms for BR2 and BV3, respectively. Besides, based on enthalpy values (16.30 and 30.26 kJ/mol for BR2 and BV3, respectively), the simultaneous adsorption of both dyes was endothermic while the entropy revealed a higher affinity of the investigated adsorbent to BV3. The sorption process in separate systems (BR2 and BV3) was thermodynamically feasible for both dyes with negative free enthalpy values. The comparison to single systems showed an increase of affinity for BV3 contrarily to BR2 and, a decrease of spontaneity with higher extent for BR2.