Utilization of avtivated carbon produced orange (Citrus sinensis L.) pulp for adsorption of reactive dye from aqueous solution

Activated carbon is the most widely used adsorbent. It can use removal of heavy metals, organic compounds, dyestuffs from aqueous solution through the high surface area and pore volume. However, the price of activated carbon is high. Its use is limited due to the high cost, and therefore it led to search for low-cost adsorbents. Recently, it has increased an interest in the production of activated carbon from agriculture and forestry waste. In this study, activated carbon was produced from orange (Citrus sinensis L.) pulp, which obtained fruit juice industry by chemical activation with zinc chloride (ZnCl2). The orange pulp was mixed with ZnCl2 in the impregnation ratio of 3:1. Carbonization of the impregnated sample was carried out at 500ºC, heating rate of 5ºC/min, under the nitrogen flow (200-300 cm3/min) and held for 1 h at this final temperature. BET surface area and micropore area of obtained activated carbon was 1779,48 m2/g and 1383,20 m2/g, respectively. As the carbon content increased after activation process, hydrogen and oxygen content decreased. The activated carbon used removal of Orange 13 from aqueous solutions. Effects of adsorbent dossage, solution pH, temperature, initial dyestuff concentration and contact time on the adsorption process was examined. The suitability of various equilibrium izoterm (Langmuir, Freundlich and Dubinin-Radushkevich) and kinetic (pseudo-first-order, pseudo-second-order, intraparticle diffusion) models on adsorption process were investigated. Equilibrium isotherms were well described by Langmuir equilibrium isotherm equation. The adsorption capacity was about 147, 222 and 263 mg/g at 25, 35 and 45ºC, respectively. Adsorption kinetics were fitted with the pseudo-second-order equation and the adsorption rate is controlled by film diffusion with intraparticle diffusion. Thermodynamic parameters (ΔHº, ΔSº, ΔGº) were calculated. The positive value of enthalpy (ΔHº) shows that the adsorption process is endothermic, the negative values of Gibbs free energy (ΔGº) indicate that the spontaneity of the adsorption process and the positive value of entropy (ΔSº) shows the increasing of randomness at the adsorbent–solution interface. According the results, prepared activated carbon can be used as a low-cost adsorbents for the removal of Orange 13 from wastewater.