Removal of Congo red from aqueous solutions by adsorption onto illite clay

Many synthetic dyes are toxic and must be removed from industrial effluents to prevent critical environmental and health problems. Adsorptive technologies are favored and several adsorbents have been tested for this purpose. Efficiency, economic suitability, and environmental compatibility are the most critical criteria in the selection of an adsorbent. The focus of the present study was the adsorption of Congo red (CR), an anionic diazo dye, from aqueous solutions using illite mineral. The Brunauer–Emmett–Teller surface area of the mineral tested in the study was 44.73 m2/g. Solution pH had a significant effect on the process, with the highest adsorption efficiency (AE) at pH 5.7. The process reached equilibrium after 2 h and the relevant data were in good agreement with the pseudo-second-order kinetic model. Adsorption efficiency decreased with temperature; the process was exothermic and non-spontaneous, according to thermodynamic data. The isotherm curves were fitted with Type I adsorption, and adsorption capacity increased with illite dosage but was negatively impacted by initial CR concentration. The highest adsorption capacity was 61.02 mg/g, and the equilibrium data were well described (R2 = 0.999) by the Langmuir isotherm model. This study demonstrates that illite mineral can be used for the remediation of the anionic diazo dye Congo red by adsorption.