The Study Of Metals-EDTA Containing Wastewater Treatment By Fe/C Internal Micro-electrolysis Coupled With Fenton Process

As traditional physical and chemical processes fail to break complex thoroughly,electroplating wastewater is always hard to be treated.Fe/C internal micro-electrolysis process has the advantage of economy and simple operation in the treatment of complex wastewater,but still exist the disadvantage of low decomplexation efficiency and insufficient advanced treatment.In order to give full play to the advantage of IE and Fenton,to achieve the goal of breaking complex thoroughly,improving heavy metals removal efficiency and to promote the EDTA degradation,a type of internal micro-electrolysis(IE)coupled with Fenton process was designed.For the purpose of providing technical guidance and theoretical basis about treating meatals-EDTA wastewater by IEF process,a systematic study of the coupling way and the corresponding mechanism of IEF process,the efficiency and process conditions of IEF process treat on Cu-EDTA simulation wastewater,Cu-EDTA and Ni-EDTA simulation mixed wastewater,and the degradation products and pathways of EDTA were performed.IEF process has much higher treatment efficiency compared to sole IE or Fenton process,which can effectively remove heavy metal ions and degrade complexing agents.IEF process has an excellent ability to efficiently decomplex and remove organics,which can be proved by the results.Removal efficiencies of Cu2+ and TOC removal efficiencies were 99.57% and 83.57%,respectively,and when 50 mg/L Cu-EDTA wastewater was treated by IEF process for 40 min,the residual TOC and EDTA in effluent were 21.44 mg/L and 7.16 mg/L,respectively.Batch experimental results indicated that the treatment efficiency of IEF process increases with the decrease of pH and initial concentration of EDTA-Cu(II).Appropriate ranges for the iron scrap dosage,Fe/C and Fe2+/H2O2 are 30-50 g/L,2:1-4:1 and 1:3-1:5,respectively.The time of front IE process and the subsequent Fenton process should be controlled in 15-25 min and in 20 min,respectively.In this study,an empirical equation 90= 0.91 1-0.51 22.00 30.12 and ORP index were proposed to flexible control IE and Fenton process,respectively.The parameters of iron dosage,initial pH and Cu-EDTA concentration could be flexible controlled by the equation.H2O2 dosage could be controlled by the ORP index.The results showed that Cu2+,TOC and EDTA removal efficiencies were 99.6%,80.3% and 83.4%,respectively,under the proper operation conditions of iron dosage of 30 g/L,Fe/C of 3/1,initial pH of 3.0,Fe2+/H2O2 molar ratio of 1/4 and reaction time of 20 min respectively for IE and Fenton process.The influence rule of the main effects by IEF process in treating the Cu-EDTA and Ni-EDTA mixed wastewater were the same that of the sole Cu-EDTA wastewater,such as iron dosage,initial pH and H2O2 dosage.Under the same operation conditions,when the conentration of Cu-EDTA and Ni-EDTA were 50 mg/L and 20 mg/L,Cu2+,Ni2+ and TOC removal efficiencies were 99.34%,95.90% and 82.31%,respectively.These results showed that IEF process not only could efficiently treat sole Cu-EDTA wastewater,but also could efficiently treat Cu-EDTA and Ni-EDTA mixed wastewater.The main reaction mechanism of IEF process could be summarized as: Fe2+-based redox and oxidation,electrophoresis effect,the active hydrogen stems and adsorption coprecipitation in front IE process,and the advanced oxidation of ·OH in subsequent Fenton process.IE process was mainly set to remove most of the heavy metal ions and a few complex anion,while the subsquent Fenton process can further remove heavy metal ions and most complex anion.The removal of heavy metal ions by IE process were effected by many functions,which play synergistic roles in each other.Moreover,the order of the contribution of these effects were Fe3+ replacement > the active hydrogen stems and micro-electric field > adsorption by the ferrous and ferric hydroxides > others.Additionally in Fenton process,·OH played an important role in the degradation of EDTA,which lead to a tendency of cleavage in the first step of degradation of C-C and C-N bonds of EDTA,and to the final degradation into small molecule acid.Main intermediates were nitrilotriacetic acid(NTA),3-(Diethylamino)-1,2-propanediol,amino acetic acid,pentanoic acid,propionic acid and acetic acid,etc.A possible degradation pathway of EDTA in IEF process was proposed.Kinetics analysis indicates that the removal of Cu2+ and Ni2+ in IE and Fenton process all followed pseudo-first-order kinetics.IEF process has excellent color and COD removal performance when used as advanced treatment process of metals-EDTA wastewater.None dose additional ferrous salt,Less the amount of H2O2,which was about 200 mg/L.The solution pH was increased from 3.0 to 6.5 after reacted in the IE and Fenton process,avoid to repeated adjust the solution pH,which beneficial to the subsequent flocculation precipitation process.