Study On Activation Of H₂O₂/?NH₄?₂S₂O₈ By Lignite Pyrolysis Product For Nitroaromatic Compounds Degradation

Direct combustion of lignite exhibits low efficiency and high operation cost,and causes air pollution.Lignite pyrolysis technology is one of the solutions for the efficient utilization of lignite.In recent years,researchers have demonstrated that persistent free radicals?PFRs?can be produced from the transition metal oxide and aromatic group during the biomass pyrolysis process.Since lignite has abundant surface oxygenic functional groups and redox-active metals such as iron,this study investigated the types and concentrations of the PFRs generated by lignite pyrolysis at different temperatures.Then the degradation efficiency of nitroaromatic compounds by hydrogen peroxide and persulfate activated with lignite pyrolysis product was investigated.The types and concentrations of PFRs in Xinjiang lignite pyrolysis products at 200,400,600,and 800°C?L200,L400,L600,and L800?were analyzed.According to electron paramagnetic resonance?EPR?spectra,the concentrations of PFRs increased with the temperature increased from 200 to 600°C,while decreased when the temperature was elevated to 800°C.The g factors in the EPR spectra were all above 2.0040,indicating that all the generated PFRs were oxygen-centered radicals.The degradation of p-NA?25 mg/L?was enhanced after the addition of lignite pyrolysis product and H₂O₂,and the degradation efficiency increased with the increasing of pyrolysis temperature?200⁶00°C?,lignite product concentration?0.5⁴ g/L?,and H₂O₂ concentration?10¹00 mM?during 24 h of reaction.The activation of persulfate by lignite pyrolysis products for p-NA and p-nitrophenol degradation were also studied.The results indicated that the SO₄^-·was produced during the activation of persulfate by the lignite pyrolysis product,and the SO₄^-·could react with the aqueous OH^-with the generation of hydroxyl radicals?·OH?.The degradation efficiency of p-NA increased with increasing the pyrolysis temperature?200⁶00°C?,lignite pyrolysis product concentration?0.5⁴ g/L?,and persulfate concentration?4³2 mM?after 24 h of reaction.In addition,8?M Fe³⁺and Ni²⁺loaded on lignite and the PFRs in modified pyrolysis product?L600-Fe and L600-Ni?were increased from 1.48×10¹⁷ spins/g to 1.77×10¹⁷ and 1.82×10¹⁷spins/g,respectively.The g factors were increased from 2.0041 to 2.0035 and 2.0035,indicating that the type of PFRs was changed from oxygen-centered radical to carbon-centered radical.Meanwhile,in comparison to the unmodified pyrolysis products,the degradation efficiency of p-NA separately activated by L600-Fe and L600-Ni increased from 48.2%to 93.2%and 95.3%.The concentration of 8?M Ni²⁺and 5 mM CT co-loading on lignite and the modified pyrolysis product?L600-Ni/CT?was increased to 3.04×10¹⁷ spins/g.The degradation efficiency of p-NA separately activated by L600-Ni/CT reached 100%in 7 h.