Natural coal gangue as a stable catalyst to activate persulfate: tetracycline hydrochloride degradation and its explored mechanism

Coal gangue (CG), a kind of kaolinite-rich solid waste, is produced in coal washing and mining. Its massive accumulation causes serious environmental pollution. Therefore, the comprehensive utilization of CG is urgently needed. This work found that natural kaolinite-rich CG could efficiently activate persulfate (PS) to degrade tetracycline hydrochloride (TC) in the absence of light, electricity, heat, or other energy sources. The degradation efficiency and total organic carbon (TOC) removal efficiency could reach nearly 70% within 10 min and 55.3% within 60 min, respectively. The capture experiments and electron spin resonance (ESR) tests showed that SO4-, OH, O-2(-), and O-1(2) participated in the process of TC degradation. Mechanism investigation indicated that the abundant hydroxyl groups on CG surfaces contributed most to the excellent adsorption performance toward PS and hence played critical roles in the PS activation and TC degradation process. This work offers an example of an effective utilization of a natural solid waste in pollution treatment to realize waste control.