Evaluation of olive pomace for the separation of anionic dyes from aqueous solutions: kinetic, thermodynamic, and isotherm studies

Abstract

Today, water pollution is one of the major problems threatening human health. Synthetic dyes from industrial effluents are among the many toxic compounds that cause water pollution. The aim of this study is the evaluation of olive pomace (OP) to be used as a biosorbent during the separation of two anionic dyes, Congo Red (CR) and Methyl Orange (MO), from aqueous solutions by adsorption technique. The biosorbent was characterized using Fourier transform infrared, Brunauer-Emmett-Teller, Barrett-Joyner-Halenda, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. It was shown to be largely unaffected by pH, indicating that OP can be utilized over a wide pH range. Experiments were conducted without pH adjustment of aqueous solutions. Kinetics showed that adsorption followed the pseudo-second-order kinetic model and reached equilibrium in 210 min. Efficiency reduced with the increase in temperature and thermodynamic parameters indicated that physical or physico-chemical interactions may have occurred between the dyes and OP. The process was exothermic and non-spontaneous. The efficiency was negatively influenced by initial dye concentration while positively affected by the OP dose. The trend was reversed for adsorption capacity, resulting in maximum values of 145.0 and 257.4 mg/g for CR and MO, respectively. These were higher than those reported in the literature for the sorption of these dyes using various types of waste materials. The process was well-explained by Freundlich isotherm for both dyes. The OP was found to be effective for the separation of anionic dyes from aqueous solutions over wide pH and concentration ranges.