Application of Mg-Fe Layered Double Hydroxides/Biochar Composite for the Removal of La(III) from Aqueous Solutions

As a valuable strategic resource, rare earth elements are widely used in various high-end industries, however, the environmental pollution and resource recovery caused by them have also attracted wide attention. In order to remove La(III) from aqueous solution by adsorption, Mg-Fe layered double hydroxide (MgFe-LDH) was loaded onto biochar (BC) through co-precipitation method to synthesis Mg-Fe layered double hydroxide/biochar composite (HBC) in this study. Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), specific surface area test (BET), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and X-ray photoelectron spectroscopy (XPS) were used to analyze the physical and chemical characteristics of the materials. The effects of various factors on the adsorption of La(III) by HBC were investigated. Under the optimal conditions of temperature = 308 K and pH = 6.0, the adsorption efficiency of 20 mg/L La(III) solution by 0.60 g/L adsorbent reached 97.81% within 24 h. The HBC showed good regeneration and reuse performance, the adsorption capacity of the regenerated HBC for La(III) still maintain 75.75% of the first adsorption capacity after 5 cycles. Moreover, kinetic and isothermal model fitting analysis showed that the adsorption is consistent with the pseudo-second-order kinetic model and the Langmuir model with maximum adsorption of 42.01 mg/g. Additionally, E s calculated through the D-R model is 23.12 kJ/mol, indicating that the adsorption is monomolecular and mainly chemisorption. Thermodynamic analysis demonstrated that the spontaneous endothermic process of adsorption La(III) on HBC. Overall, this study illustrates that the prepared HBC can be used as carbon-based adsorbents for the removal of La(III) in aqueous solutions.