Fruit shell residue from Xanthoceras sorbifolia was investigated as a potential biosorbent to remove crude oil from aqueous solution. The shell powder and its carbonized material were compared while assessing various factors that influenced oil removal capacity. The structure and sorption mechanism were characterized using scanning electron microscopy and Fourier-transform infrared spectroscopy. The oil removal capacity of the raw material (75.1 mg g-1) was better than the carbonized material (49.5 mg g-1). The oil removal capacity increased with greater saponin content, indicating that hydrophobic and lipophilic surface characteristics of the saponins improved adsorption by the raw X. sorbifolia shell. An orthogonal experimental design was used to optimize the adsorption. Using 4 g L-1 of raw X. sorbifolia shell (particle size of < 0.15 mm), the highest crude oil removal efficiency was obtained using an initial oil concentration of 400 mg L-1, adsorption temperature of 30 °C, adsorption time of 10 min at a shaking speed of 150 rpm. The adsorption of crude oil onto X. sorbifolia shell was best described using a pseudo-second-order kinetic model. Raw X. sorbifolia shell material was more efficient than the carbonized material at crude oil removal from aqueous solution. This was attributable to the functional groups of saponins in raw X. sorbifolia shell. This study highlights that some agricultural and forest residues could be a promising source of low-cost biosorbents for oil contaminants from water-without requiring additional processing such as carbonization.
Keywords: Adsorption kinetics; Biosorbents; Oily wastewater; Physical-chemistry adsorption; Saponin.