| Surface treatment is a basic industry of the development of modern industry.Electroless plating, which is widely used in the aerospace, petrochemical, electronic,mechanical, textile and so on, is a basic process of surface treatment industry. However,electroless plating bath will not be able to continue to use after several times of plating.Spent electroless plating bath always have some characteristics such as containing highconcentration and complex pollutants, difficult to be treated and so on. It will causegreat harm to people’s living environment if direct emission them to the environment.So, the harmless treatment of them have been the hot spots and difficulties in the fieldof environmental protection. Ultraviolet light (UV) has the characteristics such as green,no secondary pollution, no influence on water quality and so on. This paper introducedhigh photon flux and short wave UV into catalytic oxidation process, with H2O2asoxidant, use wastewater itself contained waste metal as catalyst of advanced oxidationto oxidation of organic pollutants in wastewater, and achieving the purpose of treatingwaste by waste. Or, for the recovery valuable contaminant, recycling them and turningwaste into treasure. The effects of different parameters on the oxidation efficiency wereintensive investigated. The reasonable mechanism was also discussed.On the basis of comparing electro-optical properties of different types of UV lamps,including low-pressure, medium-pressure, high-pressure and high-strength shortwave,the phenol degradation efficiencies were also compared by different types UV catalyticoxidation process. The advantages and disadvantages of these UV lamps were alsodiscussed. Ultimately, new developed spherical high-strength UV lamp with185nmvacuum band was selected as the appropriate UV lamp of catalytic oxidation process.From the angle of using wastewater itself contained metal as catalyst to oxidation oforganic pollutants, the catalytic activity of six kinds of most common heavy metals werecompared. The results indicated that catalytic activity is in the order: Fe2+> Cu2+>Mn2+> Ni2+> Co2+> Pb2+. In addition, Fe2+, Cu2+, Ni2+, Mn2+four kind metals showedthe most possible of used in the actual production.Electroless nickel plating is one of the most typical electroless plating process. Thespent electroless nickel plating bath is not only contain high concentrations of nickeland organic pollutants, but also contain high concentration of hypophosphite andphosphite. Firstly, the hypophosphite and phosphite oxidation efficiencies by combinedhigh photon flux UV and H2O2were investigated. The results indicated that neitherH2O2nor UV alone was enough to appreciably oxidize phosphite in the90mintreatment, but the UV/H2O2process did significantly oxidize in the30min. It isbelieved that the·OH was generated by the photolysis of H2O2. Consequently, the·OHoxidized the hypophosphite to phosphite and then to phosphate. On the basis of treatment synthesized wastewater, the oxidation efficiency of electroless nickel platingrinse-wastewater, which contains2.50mmol/L hypophosphite、6.23mmol/L phosphiteand580mg/L COD, by the UV/H2O2process was investigated. At the experimentconditions of initial molar ratio of H2O2to P (including both hypophosphite andphosphite) was up to7, continuous addition H2O2mode, the initial pH=5.5, bothhypophosphite and phosphite completely oxidized in the20min and60min, respectively.90%of COD removal was also obtained in the90min. The pollutant concentration inthe spent electroless nickel plating bath was tens times higher than its rinse-wastewater.So, the treatment effect of UV/H2O2is already very limited. In order to recoveryphosphorus resource during the treatment of pollutants, the spent electroless nickelplating bath was treated by UV-Fenton process. The results indicated that not only spentelectroless nickel plating bath was treated very well, but also nickel andnanometer-sized ferric phosphate particles were recovered. Consequently, pilotexperiment was carried out. The results indicated that, deducting operating costs, itcould profit about1000yuan RMB from treatment of a ton wastewater. It couldachieve environmental and economic benefits, and has practical application value.Catalyzed by self-contained copper, the organic pollutants in the spent electrolesscopper plating bath was treated by UV catalytic oxidation process. Firstly, EDTA wasused as modal pollutant in the spent electroless copper plating bath. EDTA wasdegradated by the UV promoted copper catalytic oxidation process. The backgroundexperiment results indicated that, with180min treatment, UV/H2O2, Cu(II)/H2O2andUV/Cu(II)/H2O2three processes could remove COD about10%,44.6%and76.5%,respectively. The best COD removal efficiency was observed by UV/Cu(II)/H2O2.Secondly, the organic pollutants in the spent electroless copper plating bath was treatedby UV catalytic oxidation process, which was catalyzed by itself contained copper. Theresults indicated that, no need more copper, COD removal efficiency of82.4%wasobtained in180min of treatment. It was proved that the method of self-catalyticoxidation was practicability.With spent electroless nickel and copper plating baths as examples, the efficienciesand mechanism of spent electroless plating bath oxidation by high photon flux UVparticipated catalytic oxidation process were investigated in this paper. At the core ofhypophosphite and phosphite catalytic oxidation reaction, polymerization precipitationmechanism was elucidated in the spent electroless nickel plating baths treatment process.The recovery and utilization of high concentration phosphorus was achieved. Withself-contained copper as catalyst, a new spent electroless copper plating bath harmlessprocess was offered. Finally, on the basis of these studies, effects of UV light withorganic, catalyst and oxidant were analyzed. The free radical chain reaction mechanismof UV catalytic oxidation system was also proposed in this paper. It is believed thatthose basic research will provide theoretical and practical guidance for spent electroless plating bath treatment in the actual production. |
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