Study On The Effect And Mechanism Of Cu-EDTA Treatment By Microelectrolysis And Advanced Oxidation Process

Ethylenediaminetetraacetic acid?EDTA?,as a powerful chelating ligand with notable affinity for heavy metals ions?e.g.,CuII,NiII,Pb IIand CoII?,has been widely used in the industries.With large amounts of EDTA used in the electroless copper-plating process in the printed circuit boards?PCBs?industry,the effluent always contains high concentrations of CuII ions,forming an octahedron structure of hexacoordination with EDTA.The EDTA-chelated CuII?CuII-ETDA?complexes are considerable stable within entire pH range,thus greatly reducing the efficiency of CuII removal by conventional chemical precipitation?e.g.,OH-,S2-,CO32-?and other processes.The high toxicity of CuII-ETDA in effluents exerts serious damages to aquatic plants and living organisms,also posing great challenges for the elimination of COD/BOD by subsequent biological treatment processes.The microelectrolysis method,which uses low cost scrap as raw material,has a very good effect in the treatment of heavy metal complex wastewater.However,for the microelectrolysis in the treatment of heavy metal complex wastewater,reaction mechanism is still a lack of clear awareness.In this paper,Cu-EDTA solution was used as the research object.Microelectrolysis was used as a means of treatment.Treatment effect was compared in the miscroelectrolysis within two kinds of cathode,activated carbon and copper.The microelectrolysis method can greatly improve the removal efficiency of copper ions compared to the Fe0 method without cathodes.While using copper as the microelectrolysis of the cathode can effectively improve the reaction rate.The reaction rate constant of the pseudo-first-order reaction for copper ion removal by Fe-Cu microelectrolysis method was 0.084.The reaction rate constant of the pseudo-first order reaction of Fe-C microelectrolysis is 0.066.The analysis of the change of metal ions and pH value in Cu-EDTA solution by Fe-Cu microelectrolysis shows that the rapid decrease of copper ions in the solution is accompanied by the rapid increase of ferrous ions and total iron concentration.The results of UV spectroscopy showed that Fe³⁺-EDTA was the main product after the reaction and that the effect of microelectrolysis on EDTA degradation is limited.Infrared spectroscopy analysis of the new precipitate confirmed that the precipitate is mainly Fe?OH?3.Based on the comprehensive understanding of the apparent reaction phenomena,the complex morphological distribution of Cu²⁺,Fe³⁺ and Fe²⁺ heavy metal ions and EDTA in the pH range of 0 14 was simulated by software Visual MINTEQ 3.1.The effect of the complexation of EDTA and Cu²⁺ at pH 0 14 by gradually adding Fe³⁺ or Fe²⁺ or both Fe³⁺ and Fe²⁺ into the Cu-EDTA solution was simulated by the software.Thereby revealing the microscopic changes in the microelectrolysis process.Fe³⁺ has a good effect on the decomplexing of Cu²⁺-EDTA.The higher the Fe³⁺/Cu²⁺,the lower the pH,the better the decomplexing effect.Fe²⁺ can also effectively disassemble EDTA with Cu²⁺.The higher the Fe²⁺/Cu²⁺,the higher the pH,the better the decomplexing effect.Based on the apparent phenomena and simulation results,it can be seen that the main process of Cu-EDTA treatment by microelectrolysis is that iron dissolution produces a large amount of Fe²⁺.Then Fe²⁺ is oxidized to Fe³⁺ by dissolved oxygen.The high concentration of Fe³⁺ makes EDTA and Cu²⁺ cleave to form Fe³⁺-EDTA and free Cu²⁺.Free Cu²⁺ is removed by iron scrap,while Fe³⁺-EDTA has been partly degraded due to the reduction of iron scrap.While using ferrous ion activated persulfate to treat Cu-EDTA solution,the higher the PS/Fe²⁺,the higher the TOC removal rate,but the TOC removal rate was always lower than that by persulfate without ferrous ion.Indicating that in the reaction on the degradation of EDTA Fe²⁺ played an inhibitory effect.While treating Cu-EDTA solution with heat-activated persulfate,increasing the temperature and increasing the amount of persulfate can improve the degradation efficiency of EDTA.When the reaction temperature was 25 oC and the ratio of [PS]0/[Cu-EDTA]0 was 40/1,the removal rate of copper was 86.8% after reacting for 60 min,the removal rate of TOC was 21.1% after reacting for 240 min.When the reaction temperature was 65 oC and the ratio of [PS]0/[Cu-EDTA]0 was 40/1,the removal rate of copper was 99.6% and the removal rate of TOC was 97.8% after reacting for 40 min,indicating that EDTA has been thoroughly mineralized.At the reaction temperature of 45 oC,when the amount of persulfate was increased from [PS]0/[Cu-EDTA]0 = 5/1 to [PS]0/[Cu-EDTA]0 = 150/1,the removal rate of copper was increased from 91.1% to 98.6% after reacting for 60 min,and the removal rate of TOC increased from 35.0% to 97.9% after reacting for 240 min.The effect of heat-activated persulfate on degradation of EDTA under acidic conditions is better than that of alkaline.Therefore,the use of heat activated persulfate method followed by Fe²⁺ precipitation method can also mentain the total removal of heavy metal ions,and can effectively degrade EDTA.Cu-EDTA solution was treated by Fenton oxidation.When the initial pH was 3 and the radio rate of H2O2/Fe²⁺/[Cu²⁺-EDTA]0 was 2.5/1/0.0625,the removal rate of TOC was 77.3% after 30 min reaction,and the removal rate of copper ions was 98.6% after precitpitation by adjusting pH.Indicating that EDTA was degraded and partially mineralized during the reaction,so that the complexation function was destroyed.The iron-copper microelectrolysis method combined with Fenton oxidation method can achieve 99.4% copper removal rate and 73.1% TOC removal rate,which can ensure the complete removal of heavy metal ions and effective degradation of EDTA.It is a cost-effective complexed heavy metal wastewater treatment process.