Study On The Treatment Of Cu(Ⅱ)-EDTA Complexed Wastewater By Synergistic Activation Of Persulfate

Heavy metals in industrial wastewater usually exist in the form of complexation,because complexing agent has strong complexation ability to heavy metal ions,the traditional alkaline precipitation method can not effectively remove the heavy metals in the wastewater,so the treatment mode of“first oxidation decomplexation,then chemical precipitation”is often used.Compared with hydroxyl radical（·OH）,sulfate radical(SO₄^·-)has higher redox potential and longer half-life,which can oxidize organic pollutants in a wide p H range.Advanced oxidation process based on SO₄^·-is an effective method for the treatment of complexed heavy metals.The key is to develop efficient method of activating persulfate to release strongly oxidizing SO₄^·-and achieve the oxidative decomplexation of complexed heavy metals.In this paper,three kinds of synergistic activation methods of persulfate were developed and applied to the treatment of complexed heavy metal wastewater.The oxidation decomplexation effects on Cu（Ⅱ）-EDTA by different persulfate activation systems were investigated and the reaction parameters of the system were optimized.The main free radical species produced in different activation systems were identified and the activation mechanism of persulfate in different activation systems was further explored.The decomplexation mechanism of complexed heavy metals and the possible oxidative degradation pathway of EDTA organic ligand were explored.The main research contents are as follows:（1）Synergistic activation of PDS with alkali and heat was used to treat complexed heavy metal Cu（Ⅱ）-EDTA wastewater.There was a significant synergistic effect between alkaline activation and thermal activation.The Cu（Ⅱ）removal efficiency was21.8%by alkaline activation of PDS,and that by thermal activation of PDS was 65.7%.while Cu（Ⅱ）could be nearly completely removed within 60 min by synergistic activation of PDS with alkali and heat.·OH and O₂^·-were the main free radical species in the synergistic activation of PDS with alkali and heat system.EDTA organic ligand could be decomposed and transformed into N,N-dimethylethylenediamine,N-acetylenediamine,oxalamide,ethylamine,glycine,methylmalonic acid,oxalacetic acid,ethylene glycol,oxalic acid,acetic acid,formic acid,and was eventually mineralized into NO₃^-,CO₂ and H₂O.Under the same reaction conditions as synergistic activation of PDS（solution p H maintained at 11,temperature was 60°C）,the ferrite coating on heavy metal sludge produced in decomplexation and percipitation process not only could effectively improve the whole chemical stability of heavy metal sludge,also could increase the density and reduce the water content of heavy metal sludge.（2）Synergistic activation of PDS with alkali and MW was used to treat complexed heavy metal Cu（Ⅱ）-EDTA wastewater.There was a significant synergistic effect between alkali activation and MW activation.The Cu（Ⅱ）removal efficiency was 4.5%by alkali activation of PDS,and that by MW activation of PDS was 81.9%,while 99.9%of Cu（Ⅱ）removal could be achieved within 8 min by synergistic activation of PDS with alkali and MW.SO₄^·-and O₂^·-were the main free radical species in the synergistic activation of PDS with alkal and MW system.The precipite formed after the treatment of Cu（Ⅱ）-EDTA wastewater by synergistic activation of PDS with alkali and MW was mainly composed of CuO particles.EDTA organic ligand could be decomposed and transformed into N,N-dimethylethylenediamine,N-acetylenediamine,oxalamide,ethylamine,glycine,methylmalonic acid,oxalacetic acid,pyroracemic acid,acetic acid,and was eventually mineralized into NO₃^-,CO₂ and H₂O.The biological toxicity of Cu（Ⅱ）-EDTA wastewater was significantly mitigated by synergistic activation of PDS with alkali and MW treatment.In addition,the experiment also compared the treatment of Cu（Ⅱ）-EDTA wastewater by MW-activated PDS and MW-activated H₂O₂.The results showed that PDS has a wider range of p H application and higher utilization rate of oxidizer in MW activation reaction than H₂O₂.（3）Synergistic activation of PDS with alkali and CuO was used to treat complexed heavy metal Cu（Ⅱ）-EDTA wastewater at room temperature.The Cu（Ⅱ）removal efficiency by alone PDS oxidation was 13.5%,and that by alkaline activation of PDS was 57.0%,while Cu（Ⅱ）could be nearly completely removed within 120 min by synergistic activation of PDS with alkali and CuO.SO₄^·-and O₂^·-were the main free radical species in the synergistic activation of PDS with alkali and CuO system.EDTA organic ligand could be decomposed and transformed into N-acetylenediamine,glycine,oxalamide,ethylamine,acetic acid,ethylene glycol,methylmalonic acid,oxalacetic acid,and was eventually mineralized into NO₃^-,CO₂ and H₂O.The precipite formed after the treatment of Cu（Ⅱ）-EDTA wastewater by synergistic activation of PDS with alkali and MW was mainly composed of CuO particles.24 cycles experiments showed that CuO could maintain stable structure and sustained catalytic activity under a strong alkaline condition（solution p H maintained at 11）,which could be recycled and reused for activation of PDS.The rate constant（k value）of Cu（Ⅱ）removal gradually increased from 0.0326 min^-1 in the first cycle to 0.0491 min^-1 in the last cycle.The biological toxicity of Cu（Ⅱ）-EDTA wastewater was significantly mitigated by synergistic activation of PDS with alkali and CuO treatment.