Equilibrium isotherms, kinetics, and thermodynamics studies for congo red adsorption using calcium alginate beads impregnated with nano-goethite

• Published in: Ecotoxicology and environmental safety 2017-07, Vol.141, p.226-234
• Main Authors: Munagapati, Venkata Subbaiah, Kim, Dong-Su
• Format: Article
• Language: English
• Subjects: Adsorption; Alginates - chemistry; Congo red; Congo Red - analysis; Glucuronic Acid - chemistry; Hexuronic Acids - chemistry; Hydrogen-Ion Concentration; Iron Compounds - chemistry; Isotherms; Kinetics; Minerals - chemistry; Models, Theoretical; Solutions; Spectroscopy, Fourier Transform Infrared; Surface Properties; Temperature; Thermodynamics; Water Pollutants - analysis
• ISSN: 0147-6513; 1090-2414
• DOI: 10.1016/j.ecoenv.2017.03.036

The present study is concerned with the batch adsorption of congo red (CR) from an aqueous solution using calcium alginate beads impregnated with nano-goethite (CABI nano-goethite) as an adsorbent. The optimum conditions for CR removal were determined by studying operational variables viz. pH, adsorbent dose, contact time, initial dye ion concentration and temperature. The CABI nano-goethite was characterized by Fourier transform infrared spectroscopy (FTIR), X- ray diffraction (XRD) and Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) analysis. The CR sorption data onto CABI nano-goethite were described using Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherm models. The results show that the best fit was achieved with the Langmuir isotherm model. The maximum adsorption capacity (181.1mg/g) of CR was occurred at pH 3.0. Kinetic studies showed that the adsorption followed a pseudo-second-order model. Desorption experiments were carried out to explore the feasibility of regenerating the adsorbent and the adsorbed CR from CABI nano-goethite. The best desorbing agent was 0.1M NaOH with an efficiency of 94% recovery. The thermodynamic parameters ΔG°, ΔH°, and ΔS° for the CR adsorption were determined by using adsorption capacities at five different temperatures (293, 303, 313, 323 and 303K). Results show that the adsorption process was endothermic and favoured at high temperature. [Display omitted] •We used CABI nano-goethite which is efficient adsorbent for the removal of CR.•FTIR, XRD and SEM/EDS studies have been carried out for characterization of the CABI nano-goethite.•The maximum monolayer adsorption capacity (181.1mg/g) of CR occurred at pH 3.0.•Adsorption process fits the Langmuir isotherm and pseudo-second-order kinetic model.•Thermodynamic studies revealed that the adsorption process was spontaneous and endothermic.