Efficient Tetracycline Adsorption by KOH-Activated Yak-Dung Biochar: Mechanistic Insights

In this study, yak dung was used as a precursor to prepare biochar (KYBC600) via high-temperature pyrolysis and KOH modification for the adsorption of tetracycline hydrochloride (TCH) from aqueous solution. Compared with commonly used biomass feedstocks such as straw and fruit shells, the resource-oriented utilization of yak dung holds dual significance: it contributes to regional environmental management and enables high-value conversion of waste, underscoring its distinct regional relevance and potential for synergistic environmental governance. The physicochemical properties of KYBC600 were characterized using BET surface area analysis, FTIR, XRD, and SEM. Adsorption behavior and mechanisms were systematically investigated through kinetic, isotherm, and thermodynamic studies, supplemented by response surface methodology (RSM). The results demonstrated that the adsorption of TCH onto KYBC600 followed pseudo-second-order kinetics and the Langmuir model, with a maximum adsorption capacity of 54.10 mg·g−1. Multiple synergistic mechanisms governed the adsorption process, including pore filling, π–π stacking, electrostatic interactions, hydrogen bonding, and complexation with Ca2+, with chemical adsorption playing a dominant role. KYBC600 demonstrated excellent adsorption performance and regeneration capability across a wide pH range and in various real water matrices. This study provides novel perspectives on the resource utilization of livestock waste in plateau regions and provides a technical reference for treating low-concentration TCH-containing wastewater.