Abstract
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 (R 2 =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 cm 2 /s) than for BV3 (1.11×10 -11 cm 2 /s) when compared to individual solutions (1.24×10 -10 cm 2 /s and 1.76×10 -11 cm 2 /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.
Highlights
Cationic or basic dyes are extensively used in textile industry processes [1,2]
Models can be considered in good agreement with experimental data when R2 is close to unity and when squares of the errors (SSE), Hybrid, and Marquardt’s percent standard deviation (MPSD) values are as low as possible [50]
The adsorption in the mixture solution is endothermic since the value of enthalpy ∆H ◦ is positive for basic red 2 (BR2) (16.30 kJ/mol) and basic violet 3 (BV3) (30.26 kJ/mol) dyes (Figure 10-A)
Summary
Cationic or basic dyes are extensively used in textile industry processes [1,2]. The presence of dyes in water, even at very low concentrations, makes them unfit for human consumption [1]. As for basic dyes, they are considered to be among the most toxic molecules due to the presence of metals in their structures [1, 6]. Industrial wastewater treatment involves various methods: advanced oxidation processes, precipitation/coagulation, and biological treatment [8,9]. Such processes have some drawbacks, including high-energy requirement, consumption of chemicals, high operational cost, and the possible generation of toxic materials [10]
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