Abstract
The potential of palm spathe (PS), an agricultural waste, to remove methylene blue (MB) from aqueous solution was evaluated in a batch process. The effects of contact time (0-300 min), initial dye concentration (25-400 mg L-1), pH (2-12), temperature (25 degrees C-45 degrees C), ionic strength (0-500 mg L-1) and biosorbent dosage (0.5-6 g L-1) on the uptake of MB by PS were studied. The obtained results show that the optimum pH for MB biosorption was in the range of 5.0-10.0. Increasing the biosorbent concentration from 0.5 to 6 g L-1 caused a diminution in biosorption capacity from 59.86 to 8.01 mg g(-1). Equilibrium time increased from 120 to 270 min when the initial dye concentration increased from 25 to 400 mg L-1. When the MB concentration augmented from 25 to 400 mg L-1, the amount of MB sorbed increased from 7.83 to 62.62 mg g(-1). A rise in temperature from 25 degrees C to 45 degrees C decreased the sorption capacity from 45.28 to 42.36 mg g(-1). The removal kinetics was analyzed using the pseudo-first-order and pseudo-second-order model equations. The pseudosecond-order model was found to describe the biosorption process better than the pseudo-firstorder equation. Biosorption isotherms were modeled with the Langmuir, Freundlich, and Temkin isotherms. The data fitted well with the Langmuir isotherm. The maximum monolayer biosorption capacity was found to be 74.3 mg g(-1) at 25 degrees C. The thermodynamic parameters obtained for the sorption of MB by PS demonstrate spontaneous, exothermic, and favorable sorption process. Palm spathe may be used as an alternative biosorbent to remove MB from aqueous solutions.