Studies On Effects Of Metal Ions On The NaNO₂-Catalyzed Wet Oxidation Of Dye Pollutants

The Wet Air Oxidation （WAO） is an efficiently advanced oxidation technology,involving oxidation at high temperature （423-623K） and pressure （0.5-20MPa）condition, taking oxygen as the oxidizer, oxidizing high concentration, hazardous,toxic, and nonbiodegradable waste streams to CO2and H2O inorganic or smallmolecular organic compound. This text studied that to oxidize dyeing wastewater byCWAO.To investigate the promoting catalysis of metal ions (Cu²⁺,Ni²⁺,Mn²⁺,Co²⁺,Cr³⁺,Fe³⁺) on the NaNO₂-catalyzed wet oxidation of the anthraquinone dye, the Acid Blue129（AB129） was taken as the research substrate, and the initial AB129concentrationof100mg/L （0.22mM） coupled with the molar ratio of NaNO₂to AB129at0.6:1inacid aqueous media （pH2.5） under moderate conditions （T=150℃; oxygenpressure=0.5MPa） was used. The promoting catalysis of the different metal ions wassort by the order of Fe³⁺＞Cu²⁺＞Cr³⁺＞Co²⁺＞Mn²⁺≈Ni²⁺based on the catalyticactivity detection when the molar ratio of cocatalysts, NaNO₂and AB129was0.2:0.6:1. In addition, the decoloration rate reached100%after2h of catalytic wetoxidation in the NaNO₂/FeCl₃system. The variation of COD of the solution showedthat the NaNO₂/FeCl₃coupling system was better than the Fe³⁺or NaNO₂catalysisalone. After4h of catalytic wet oxidation, the COD removal rate reached68%in thepresence of NaNO₂/FeCl₃, and the increment of COD removal rates compared with theFe³⁺and NaNO₂alone were21%and45%, respectively. The UV-visible spectrumanalysis as well as the COD determination indicated that the final products of theAB129degradation were CO2and small molecule organic compounds.The reaction mechanism of NaNO₂/FeCl₃coupling system was studied by theaddition of free radical scavenger. For O-2the capture agent is benzoquinone, for theOH, the main scavenger are Br-and isopropyl alcohol. From the decolorization rateand UV-visible spectra of adding the benzoquinone and Br-, the more the amount ofscavenger, the more the degradation effects of the AB129, which played a certaindegree of inhibition. For the addition of the isopropyl alcohol, the decolorization rateincreased with the amount of scavenger. However isopropyl alcohol decreased theproduction of OH and inhibited the catalytic degradation of aromatic rings bycombining with the UV-visible spectra analysis. As a result, a probable mechanism ofthe stimulative catalytic oxidation was proposed by the cycle and transformation of M^（n+1）+/Mn⁺、NO、NO₂and ONOOH, while ONOOH and cocatalysts were consideredas the most important active oxidants.