Thallium separation from wastewater using α-FeOOH@Biochar: Efficacy and mechanism

Thallium (Tl) is an untraditional toxic metal. Emerging Tl pollution has received increasing concerns. Despite its extreme biotoxicity, Tl is an irreplaceable element for specific high-tech fields (e.g., superconductors, semiconductors, and optical fibers) due to its peculiar physio-chemical properties. Besides, Tl has been also regarded as critical strategic metal owing to its low abundance and scarcity in the earth’s crust. Herein, a novel composite of α-FeOOH@BC was facilely synthesized via biochar modification with environmentally abundant iron oxides (α-FeOOH) to separate Tl(I) from wastewater. The results showed that overall large distribution coefficient values ( K d  > 5000 mL/g) of Tl separation by α-FeOOH@BC in a wide pH range (5.0–11.0) were achieved, suggesting a generally promising Tl separation capacity. Multiple characterizations with Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) indicate that the dominant Tl separation mechanisms included electrostatic attraction, ion exchange and complexation. These findings indicate that the α-FeOOH@BC material may have important application in Tl separation from industrial wastewaters, which are usually moderately acidic with pH values ranging from 5.0 to 7.0. This study offers novel perspectives on using environmental abundant iron oxides modified biochar for easy and fast separation of Tl from industrial wastewater. All these findings can facilitate to develop waste-to-resources strategy for recycling Tl in the loop of circular economy and industrial symbiosis.