Pine needle–derived biochar adsorbents for removal of Sm(III) and competitive toxic metals from model aqueous matrices

Abstract

Pine needle–derived biochars have been prepared and investigated as adsorbent materials for the removal of trivalent samarium (Sm(III)) from aqueous systems. The biochars, which were previously oxidized and magnetized), have been characterized prior and after Sm(III) adsorption by Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray diffraction (XRD). The effect of various parameters such as metal ion concentration, pH and contact time on the adsorption efficiency has been investigated. In addition, competitive adsorption experiments have been carried out (competition between Sm3+, Cu2+ and UO22+ ions) by means of batch type experiments. The results showed better adsorptive properties for magnetized oxidized pine needle biochar (PNCOM), particularly at pH 6 (qmax = 691.7 mg·g−1), while at pH 3 the oxidized biochar (PNCO) (qmax = 285.7 mg·g−1) presented the highest adsorption capacity. The experimental data were better fitted by the Langmuir adsorption and pseudo-second order kinetic model. On the other hand, the competitive adsorption studies have shown that generally PNCOM presents remarkably higher affinity for U(VI) than its non-magnetized counterpart (PNCO). However, despite the fact that the sorption capacity is the highest for U(VI), the affinity of the biochar materials for the studied metal ions is higher for Sm(III), followed by U(VI) and Cu(II). This indicates that the net charge of the metal ion is a key parameter regarding the stability of the complexes formed on the oxidized biochar materials prior and after magnetization.