Effect of KOH treatment on bituminous coal for the effective removal of Basic Blue 41 dye from aqueous solutions

Activated carbons (ACs) were produced from Zonguldak region bituminous coal using physical and chemical techniques and evaluated for the removal of a textile dye, Basic Blue 41 from aqueous solutions. The color removal performance of ACs prepared by physical activation (PAC), chemical activation with KOH (CAC), and the commercial AC were compared; and the effects of adsorbent preparation method, temperature, and initial dye concentration on adsorption were studied. BET surface areas of the PAC, AC, and CAC were determined as 52.6, 824, and 1,312 m2 g-1, respectively. Micropore volume of PAC determined by DR method was 0.02 cm3 g-1, whereas AC and CAC have values of 0.42 and 0.57 cm3 g-1. Thermal treatment with KOH resulted in enhancement of the porosity characteristics, particularly in micropores, and the surface area of the CAC samples. The batch adsorption experiments were carried out isothermally at 25–35°C. The values for the adsorption capacity Q0, determined from the Langmuir model at 25, 30, and 35°C were 96.4, 52.1, 54.7 mg g-1 for PAC; 262.5, 283.3, 293.3 mg g-1, for AC; and 420.2, 427.4, 460.8 mg g-1 for CAC, respectively. The increase in adsorption capacity with an increase in temperature for BB 41 onto CAC and AC indicated an endothermic chemisorption process, which was attributed to increased surface coverage at higher temperature and creation of reactive and active sites. For BB 41 adsorption onto PAC, the decrease in sorption capacity with increasing temperature indicated the exothermic behavior of the sorption process that is related to physisorption. The adsorption capacity of the obtained samples was found in the order of CAC > AC > PAC. Among the AC samples prepared by different methods, the highest value of the adsorption capacity obtained was 460.8 mg g-1 at 35°C for CAC. Kinetic data were adequately represented by the pseudo-first-order kinetic model. AC prepared from coal by CAC treatment was shown to be an effective adsorbent for the removal of BB 41. © 2016 Balaban Desalination Publications. All rights reserved