Full-Component Valorization of Coal Gangue: Interfacial Synergy in Metal Ion-Derived Layered Oxides and SiO2-Supported Composites for PMS Activation and Tetracycline Adsorption

It is crucial to achieve the valid treatment and reuse of solid waste coal gangue (CG). This work extracted Al and Fe elements from solid waste coal gangue (CG) for the synthesis of layered double hydroxides (NiAlFe-LDHs), which were then converted to layered oxides (LDOs) via calcination to activate peroxymonosulfate (PMS) for rhodamine B (RhB) degradation. NiAlFe-LDOs/SiO2 was also synthesized utilizing leached CG (SiO2) as an inorganic support through thermal treatment of NiAlFe-LDH/SiO2 under an air atmosphere. Due to the different structures and physicochemical properties, NiAlFe-LDOs and NiAlFe-LDOs/SiO2 displayed different removal performance toward organic pollutants. LDO-400 exhibited an outstanding RhB degradation efficiency of about 96% within 20 min in the PMS activation system, and it also showed excellent cycling stability with about 82% degradation efficiency after the eighth cycle. The toxicity of RhB and its degradation intermediates was simulated via ECOSAR software to evaluate the environmental safety of the degradation process. For practical application, LDO@sodium alginate (SA) gel beads were synthesized and employed in a fixed-bed reactor, which maintained a degradation efficiency exceeding 90% after 96 h of continuous operation. Other than the excellent RhB degradation efficiency of LDO-400, LDO/SiO2-400 showed a more remarkable adsorption efficiency of 95% toward tetracycline hydrochloride (TC, 50 mg·L–1) within 40 min compared with LDO-400 (54%) and SiO2 (7%). This work not only provides an effective strategy for aquatic pollutant removal but also realizes the comprehensive utilization of CG as an inorganic non-metallic raw material.