Study On The Treatment Of Copper-Containing Complex Wastewater By Activated Persulfate

Heavy metals have the characteristics of low toxic concentration and non-biodegradable,and often exist in industrial wastewater in the form of a mixture of ionic and complex states.Among them,free heavy metals are easy to be removed by traditional methods such as adsorption,ion exchange and alkali precipitation,but the complexed heavy metals are usually removed by“oxidation decomplexation-alkali precipitation”method due to the strong complexing force between complexing agents and heavy metals.Compared with hydroxyl radical-based advanced oxidation processes（HR-AOPs）,sulfate radical-based advanced oxidation processes（SR-AOPs）produces SO₄^·-which has the advantages of equal or even higher REDOX potential,less pH limitation and longer half-life.Therefore,to find a reasonable effectively activate persulfate（PS）method is the key to dealing with complex state of heavy metal.In this paper,Cu（Ⅱ）-EDTA was used as the target pollutant,and three different PS activation methods were developed to study the decomplexation of Cu（Ⅱ）-EDTA.The removal of Cu（Ⅱ）-EDTA,identification of free radical species and possible degradation paths of Cu（Ⅱ）-EDTA were discussed.The main conclusions are as follows:（1）The effect of alkali activated peroxymonosulfate（PMS）and alkali activated peroxydisulfate（PDS）on Cu（Ⅱ）-EDTA was compared.The results showed that when the concentration of Cu（Ⅱ）-EDTA was 1.57 m M,the ratio of[Cu（Ⅱ）-EDTA]/[PMS]was 1:25,and the pH was maintained at 7.0±0.2,93.20%of Cu（Ⅱ）could be removed after 60 min of reaction.At the same concentration of Cu（Ⅱ）-EDTA,[Cu（Ⅱ）-EDTA]/[PDS]was 1:25,pH was maintained at 11.0±0.2,only 62.75%of Cu（Ⅱ）can be removed after 240 min reaction.The free radical capture experiment showed that in the alkali activated PMS system,the main radicals involved in the decomplexation were SO₄^·-and O₂^·-,while in the alkali activated PDS system,·OH and O₂^·-were the main radicals in the Cu（Ⅱ）-EDTA decomplexation.According to gas chromatography-mass spectrometry（GC-MS）and ion chromatography（IC）analysis,the main degradation products in alkali activated PMS system included acetic acid,ethylamine,oxaloacetic acid,glycine,N-Acetylethylenediamine,oxalamide,formic acid and other organic intermediates,and some of them were mineralized as CO₂,H₂O,NO₂^-and NO₃^-.The main intermediates produced in the alkali activated PDS system were N-Acetylethylenediamine,ethylamine,glycine,ethoxyethanol,ethylene glycol,oxaloacetic acid,formic acid,oxalamide and glycolic acid,some of which were mineralized as CO₂,H₂O and NO₂^-.The actual electroplating wastewater can be discharged up to the standard by alkali activated PMS.（2）Cit-Fe（Ⅲ）was used to activate PDS under visible light to treat Cu（Ⅱ）-EDTA wastewater.The results showed that when the concentration of Cu（Ⅱ）-EDTA was 1.57m M,[Cu（Ⅱ）-EDTA]/[PDS]was 1:15,the dosage of Fe（Ⅱ）was 200 mg/L,and[Fe（Ⅱ）]/[Citrate]was 1:0.75,98.63%Cu（Ⅱ）was removed after 120 min of the decomplexation reaction.Although the removal efficiency of Cu（Ⅱ）-EDTA can be improved by increasing the dosage of PDS,Fe（Ⅱ）and citrate,the excessive concentration of PDS and citrate in the system will inhibit the decomplexation of Cu（Ⅱ）-EDTA.In the initial pH range of 2.92～11.0,the PDS/Fe（Ⅱ）/Citrate/VL system can achieve efficient removal of Cu（Ⅱ）-EDTA.According to the free radical trapping experiment,SO₄^·-and O₂^·-were the free radicals mainly involved in Cu（Ⅱ）-EDTA decomplexation in the PDS/Fe（Ⅱ）/Citrate/VL system.Cu（Ⅱ）-EDTA was degraded into acetic acid,formic acid,glycolic acid,N-Acetyl ethylenediamine,oxaloacetic acid,ethylamine,oxalamide,oxalamide and other acids,amines and amide organic byproducts during the collateralization process by GC-MS and IC methods.It is even partially mineralized into inorganic substances such as CO₂,H₂O and NO₃^-,and Cu（Ⅱ）was released.The emission of real electroplating wastewater can reach the standard by promoting the activation of PDS with iron citrate by visible light.（3）Cu（Ⅱ）-EDTA wastewater was treated by thermo-CuO co-activated of PDS.Results showed that when the Cu（Ⅱ）-EDTA concentration was 1.57 m M,[Cu（Ⅱ）-EDTA]/[PDS]was 1:12,the dosage of CuO was 1.0 g/L,the reaction temperature was60°C,98.68%of the Cu（Ⅱ）could be removed after 60 min of the reaction.According to the Cu（Ⅱ）removal rate constants at different temperatures,the apparent activation energy Ea was calculated as 45.43 k J/mol.Increasing reaction temperature,dosage of CuO and dosage of PDS can increase the removal efficiency of Cu（Ⅱ）-EDTA,but increasing the initial pH value had no obvious effect on the decomplexation of Cu（Ⅱ）-EDTA.The results of free radical trapping experiments showed that SO₄^·-and O₂^·-were the main free radicals produced in thermo-CuO co-activated PDS system.The intermediate products of Cu（Ⅱ）-EDTA decomposed into N-Ethylformamide,N-Acetylethylenediamine,formic acid,oxaloacetic acid,dimethylamine,ethylamine,glycine,oxalamide,acetic acid and other small molecules of organic matter were characterized by GC-MS and IC methods.Inorganic substances such as CO₂,H₂O,NO₂^-and NO₃^-are also produced.Through the thermo-CuO co-activation PDS,the real electroplating wastewater can be discharged to the standard.