Insights into thallium adsorption onto the soil, bamboo-derived biochar, and biochar amended soil in Pomelo orchard

Little information is available on thallium (Tl) adsorption onto biochar amended soil for a relatively long term. In this study, bamboo-derived biochar (BDB), soil in pomelo orchard (SP), and biochar amended soil in pomelo orchard (BSP) were thus used to evaluate the potential remediation of thallium (Tl) using batch-adsorption techniques. Furthermore, we characterized the above-mentioned sorbents' properties related to Tl adsorption to understand Tl's adsorption mechanisms. The results showed that BDB, SP, and BSP achieved equilibrium adsorption capacity of 96.9, 95.43, and 96.76%, respectively, within the initial 15 min. This means that compared to other sorbents, BSP exhibited an efficient sorbent for Tl remediation even when applied in the agricultural field for one year. Multi-layer adsorption played a dominant role in the adsorption of Tl, which was supported by the suitability of Freundlich model for describing the adsorption behavior of Tl onto the selected sorbents. In addition, the pseudo-second kinetic order models strongly fitted Tl's adsorption onto BDB, SP, and BSP, indicating that the process was accompanied by chemical adsorption. Observed on the surface of BDB by a Fourier Transform Infrared Spectrometer (FTIR) and an X-ray photoelectron spectroscopy (XPS), the presence of O-H groups and PO43- might promote chemical adsorption of Tl onto BDB. Overall, these findings can provide insights into comprehensively developed bamboo-derived biochar technology to remediate Tl contamination in agricultural soils.