Estimating in situ prepared alkaline soluble flavan as an advanced adsorbent for rare earth elements

Abstract

Abstract The design and synthesis of organic adsorbents for rare earth element (REEs) separation remain significant scientific aspect and industrial endeavor. In a single-pot reaction, acetone and resorcinol in acidic media over a two-day period facilitated the formation of the 2, 4, 4-trimethyl-7, 2′, 4′ trihydroxy flavan (flavan adsorbent). Under acidic conditions, flavan effectively adsorbs REEs (adsorbate), while under alkaline conditions, flavan rapidly dissolves completely. A series of adsorption experiments was conducted to determine the optimal adsorption conditions, including pH variations (1–5), REEs solution concentrations (250–1000 mg/L), adsorption time (5–60 min), and flavan mass (10–100 mg). The maximum adsorption capacity for flavan under optimal conditions was 258 mg g−1. Various analytical instruments were employed for flavan characterization, including Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), which were essential for analyzing the surface morphology and structural properties of the flavan. Adsorption isotherms suggested that the adsorption of REEs onto the flavan surface followed the Langmuir model, which in turn exhibited a theoretical adsorption capacity of 263.2 mg g−1 better off the Freundlich model. Kinetically, the adsorption of REEs on the flavan is best run in a pseudo-second-order model trajectory, which in turn exhibited an adsorption capacity value of 283 mg g−1. Interference studies revealed that flavan is a selective adsorbent; however, aluminum ions may exert a minor interference effect of 4% (in term of REEs uptake). Other competing elements, including Na, K, Mg, Ba, Mn, Cu, Fe, and Sn, exhibited a minimal decline in flavan uptake for REEs.

Keywords

• Rare earth elements
• Adsorption
• Flavan
• Characterizations
• Alkaline soluble adsorbent
• Adsorption isotherm