The potential use of straw-derived biochar as the adsorbent for La(III) and Nd(III) removal in aqueous solutions

Recent attention on the lanthanides (Ln) contaminant such as lanthanum (La) and neodymium (Nd) extensively used in industry has aroused the great desire for the effective adsorbent. Biochar, relying on its high selectivity and optional ease, is regarded as a promising adsorbent for lanthanides removal although the evaluation of the efficiency and mechanism of La(III) and Nd(III) adsorption on biochar still lags. Here, we investigated the aqueous adsorption processes through SEM, TEM, EDS, FTIR and Raman spectra, XPS, and batch experiments. The porous structure of biochar and the complex functional groups on its surface contributed to the La(III) and Nd(III) removal processes. The kinetic of La(III) and Nd(III) adsorption agreed well with the pseudo-second-order kinetic model. The adsorption capacity showed a strong positive correlation with pH value. However, it was only slightly altered and robust in La(III) and Nd(III) adsorption respectively. The isotherm results reflected significant fitting to the Sips model as well as Langmuir and Freundlich model. Thermodynamic demonstrated the spontaneity, endothermic nature, and temperature favor of the adsorptions on biochar surface (La: Delta H-0=35.39 (kJ/Mol), Delta S-0=104.71(J*Mol(-1)*K-1) and Delta G(0)<0; Nd: Delta H-0=16.71(KJ/mol), Delta S-0=119.41(J*Mol(-1)*K-1) and Delta G(0)<0). Both the La(III) and Nd(III) removal processes combined physical and chemical adsorptions. Therefore, biochar could be a potential green material for the lanthanum and neodymium adsorption with high efficiency.

Automated summary

Recent research on the adsorption of lanthanum (La) and neodymium (Nd) on biochar demonstrates that the porous structure and complex functional groups on biochar surface contribute to the efficient removal of these lanthanides. The adsorption processes follow the pseudo-second-order kinetics and show a strong positive correlation with pH value. Thermodynamic analysis indicates that the adsorptions are spontaneous, endothermic, and favored at higher temperatures on the biochar surface, combining both physical and chemical adsorption mechanisms for effective removal of La and Nd.