Study of the Adsorption of Methylene Blue from Aqueous Solution: a Comparison between Iraqi & English bentonite Activity as Adsorbents


Background: Methylene blue dye uses as adsorbent to study the ability of different surface activities as adsorbents. The adsorbents can be used in the extraction of certain pollutant substances from solution on solids which is one of the cheapest and easiest separation methods. Furthermore, some of the extracted substances are economically important. In previous work, the ability of English bentonite to extract methylene blue dye from aqueous solution was carried out. In this work, Iraqi locally bentonite was used as a cheaper adsorbent for methylene blue from aqueous solution. The second aim of the present study is to make a comparison between English bentonite and Iraqi bentonite in different parameters of adsorption of Methylene blue dye from aqueous solution. Some practical parameters affecting adsorption process, in both clays, such as initial dye concentration and the thermodynamic parameters (ΔHº, ΔGº, ΔSº) for the adsorption process also computed and compared. Materials and Methods: Ten milliliters of different concentrations of methylene blue solutions (5, 10, 15, 20, 25, 30, 35, 40, 45, 50 mg/L) were mixed in water shakerbath with 0.05g of bentonite clay. Supernatants were separated by centrifugation. UV-Visible spectrophotometer technique used to follow up the adsorbed quantities after mixing the dye solution with bentonite. The experiment repeated at three different temperatures (5, 25, 45°C) to measure the thermodynamic parameters (ΔHº, ΔGº, ΔSº) for the adsorption process. Results: The extent of the methylene blue removal by Iraqi bentonite increased with increase in the initial concentration of the dye and with decrease temperature. Thermodynamic parameters, such as ΔHº, ΔGº, and ΔSº have been calculated by using the thermodynamic equilibrium coefficient obtained at different temperatures and concentrations. Iraqi bentonite :( ΔHº=-32.04 KJ.mol-1, ΔGº=-14.78 KJ.mol-1, ΔSº=-57.91J.mol-1. ºK-1). English bentonite: (ΔHº=20.21 KJ.mol-1, ΔGº=-5.17KJ.mol-1, ΔSº=85.16 J.mol-1. ºK-1). Conclusion: Both English and Iraqi bentonite clays have ability to adsorb methylene blue. The dye removal increased with increase in the initial concentration of the dye. There is no significant difference in the amounts of dye adsorbed by both clays indicated the possible symmetry in the active sites of bentonite clays even they come from different origin. Thermodynamical data indicate that the adsorption of methylene blue on Iraqi bentonite is exothermic and spontaneous and high heat of adsorption indicates possibility of chemisorption process in addition to other ordinary forces including in adsorption. While same process on English bentonite is endothermic, spontaneous with very low free energy change. In conclusion, Iraqi bentonite clay is cheaper, available and has identical adsorptive activities for methylene blue. This research opens a series of studies for the uses of this Iraqi bentonite as adsorbent for different substances in pollution, medicine, supporter, and different fields in industry.