Selective adsorption and recovery of scandium from red mud leachate by using phosphoric acid pre-treated pitaya peel biochar

Abstract

In recent years, the global demand for scandium has increased due to its essential role in the high-technology industry. Red mud leachates constitute a significant source of scandium and an efficient and environmentally friendly approach that attracted considerable interest. In this study, H3PO4 activated biochar (P40s) is manufactured from pitaya peel (PP) as a novel material to be used for scandium adsorption and recovery from red mud leachates. The material was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), nitrogen adsorption isotherms, X-ray photoelectron spectroscopy (XRF), zeta potential, and element analysis (such as C, H, O, N and P) to characterize adsorbents. The results indicated that the phosphorus-containing functional groups were successfully introduced to improve the physicochemical properties of biochar. The pseudo-second-order kinetic model and Freundlich isotherm fit experimental data, verifying that the scandium adsorption by activated biochar is dominated by chemisorption and belongs to multilayer sorption. The maximal adsorption capacity of 750 °C calcinated H3PO4 activated biochar (P40-750) was 20.77 mg/g. Notably, the adsorbent was better for selective recovery of Sc3+ from Al3+, Fe3+, Dy3+, Y3+ coexistence ions. The separation coefficients (SF) of scandium for aluminum, iron, dysprosium, and yttrium are 137.03, 27.04, 77.74, and 208.25 times respectively, at pH3. Importantly, scandium is efficiently extracted from the leaching solution of red mud with an 83% recovery rate. Meanwhile, P40-750 exhibited a stable scandium adsorption capacity after 5 adsorption/desorption cycles. Overall, P40-750 could be considered a low-cost and environment-friendly biosorbent for recovering scandium from red mud leaching solution.