Enhanced thallium(I) removal from wastewater using hypochlorite oxidation coupled with magnetite-based biochar adsorption

The development of efficient and regenerable adsorbent coupled with advanced oxidation for enhanced thallium (Tl) removal has been a recent focus on wastewater treatment. In this study, a magnetite-based biochar derived from watermelon rinds was synthesized and used as a sustainable adsorbent and catalyst for hypochlorite oxidation and removal of Tl(I) from wastewater. The addition of hypochlorite substantially enhanced the Tl(I) removal under normal pH range (6–9). Maximum Tl adsorption capacity of 1123 mg/g was achieved, which is 12.3% higher than the highest value previously reported. The magnetic biochar can be regenerated using 0.1 mol/L HNO3 solution for elution in only 5 min, with a Tl desorption efficiency of 78.9%. The Tl removal efficiency was constantly higher than 98.5% during five consecutive recycle tests, indicating the effective reuse performance of the adsorbent. Oxidation, surface precipitation, pore retention and surface complexation were the main mechanisms for Tl(I) removal. The re-dissolution of Tl compounds and ion exchange of Tl cations with proton were the main mechanisms for adsorbent regeneration. Given the fast oxidation rate, high adsorption capacity, steady reusability and facile separability, this magnetic biochar-hypochlorite technique is a promising means for Tl(I) removal from wastewater. The catalytic hypochlorite oxidation induced by the magnetic biochar has also great potential to the effective removal of other pollutants. [Display omitted] •Magnetite-based biochar coupled with hypochlorite oxidation enhances thallium removal.•Efficient thallium removal is achieved under normal pH of 6–9 with hypochlorite oxidation.•Capacity for adsorption of thallium from wastewater is as high as 1123 mg/g.•Thallium removal mechanisms include oxidative precipitation and surface complexation.•Magnetic biochar coupled with advanced oxidation can be extended to other field research.