Role of Potassium in Thallium(I) Removal from Wastewater Using Fruit Peels-Based Biochar

Abstract

Biochar derived from fruit peels can effectively remove thallium (Tl) from wastewater, but the role of potassium (K) in this process is underexplored. This study investigates K-rich biochars, specifically banana peel biochar, which showed high K content and excellent Tl removal efficiency. K species in these biochars were found to include loosely bound K in easily dissolvable compounds, readily exchangeable K in cationic resin-like carbonaceous polymers, and tightly bound K within the inner biochar. A positive correlation between K content and Tl removal efficiency was observed, with higher Tl removal linked to greater K release facilitated by ion exchange originated from the exchangeable K in cationic resin-like carbonaceous polymers. Adsorption kinetics followed a pseudo-second-order model, while isotherms aligned with the Langmuir model, indicating a maximum adsorption capacity of 224 mg/g at pH 5.8. Tl concentration of real acidic mine drainage was effectively reduced to below 2.0 μg/L, meeting industrial discharge standards. Characterization techniques confirmed that Tl removal primarily occurred through K-Tl-based cationic exchange and the formation of water-insoluble TlCl via chlorides-related precipitation. This study presents an efficient method for Tl remediation and elucidates the role of K from biochars in the removal of Tl from wastewater.

Keywords: biochar, Heavy metal, Adsorption, Wastewater treatment, Ion exchange