Europium removal from aqueous solutions by oxidized biochar prepared from waste palm tree fronds

Palm oil is a product of major economic importance worldwide however, palm tree cultivation generates large quantities of palm fronds as waste. In this work, the sorption of Eu3+ from aqueous solutions by oxidized biochar derived from palm tree fronds was studied at pH 3 by batch type experiments under ambient conditions. Following biochar production, the sample was oxidized using HNO3 to increase the oxygen-containing moieties on its surface. The oxidized biochar was characterized through surface and spectroscopic techniques. As indicated by the coefficient of determination value of 0.99, Eu3+ adsorption was best described by the Langmuir isotherm model. The optimum adsorption capacity was determined at qmax= 0.81 mol kg−1. Adsorption was an entropy-driven process and followed the 2nd order kinetics, reaching a plateau value of 50% relative adsorption within 60 min. Furthermore, Fourier Transform InfraRed spectroscopic data and the effect of ionic strength indicated that adsorption proceeded via the development of inner-sphere complexes between Eu3+ and the carboxylic groups on the biochar surface.