Abstract:
Heavy metal-organic complexes in industrial wastewater pose significant challenges due to their resistance to biological treatment. This study proposes the use of ferrous hydroxyl complex (FHC) to break down copper ethylenediaminetetraacetate (Cu(Ⅱ)-EDTA) and remove copper, leveraging its strong reduction and complexation capabilities. The process involves
in situ generation of CuFe
2O
4 and Cu
2O from the reduction of Cu(Ⅱ)-EDTA by FHC. These active metal species catalyze the production of hydroxyl radicals (·OH) from ozone (O
3), promoting the further mineralization of organic ligands and achieving synchronous removal of heavy metals and organic ligands. Under optimized conditions, the Fe
2+∶OH
− ratio of FHC is 1∶3, with a dosage of 2 mmol/L for FHC and 10 mg/min for O
3. This allows the complete removal of 0.2 mmol/L Cu(Ⅱ)-EDTA within 60 minutes, with no residual dissolved iron. A ratio of FHC (1∶3)∶Cu(Ⅱ)-EDTA exceeding 5∶1 ensures complete decomplexation and removal of copper. The economic efficiency of Cu(Ⅱ)-EDTA decomplexation and removal can be enhanced by increasing the proportion of OH
− in FHC rather than increasing the dosage of FHC. The process exhibits strong resistance to common anions such as chloride (Cl
−), nitrate (\mathrmNO_3^- ), and sulfate (\mathrmSO_4^2- ), indicating its practical applicability in diverse wastewater. The
in situ generated CuFe
2O
4, Cu
2O, and Fe
3O
4 after ozonation are magnetic, offering potential for magnetic separation and further enhancing cost-effectiveness. To validate the mechanism, electron paramagnetic resonance (EPR) analysis was conducted. The results confirmed that the
in situ generated products can effectively catalyze the production of hydroxyl radicals (·OH), singlet oxygen (
1O
2), and superoxide radicals (\cdot \mathrmO_2^- ) from O
3. Quenching experiments were performed to investigate the role of reactive oxidative species (ROS) in the degradation of EDTA. The results showed that the removal rate of EDTA decreased from 100.0% to 57.7% upon the addition of tert-butanol (TBA), indirectly proving the involvement of ·OH in the degradation of EDTA. Liquid chromatography-mass spectrometry (LC-MS) analysis provided insights into the reaction pathways. The decomplexation of Cu(Ⅱ)-EDTA by FHC forms iron ethylenediaminetetraacetate (Fe-EDTA), and subsequent ozonation leads to the disruption of the N—C bonds in Fe-EDTA by ·OH and O
3, generating intermediate products such as iron ethylenediaminetriacetate (Fe-ED3A), iron ethylenediaminediacetate (Fe-ED2A), glycine, Fe-nitrilotriacetate (Fe-NTA), and nitrilotriacetic acid (NTA). Further reactions may involve the substitution of acetyl groups to form Fe-iminodiacetate (Fe-IMDA) and iminodiacetic acid (IMDA), ultimately mineralizing to CO
2 and H
2O. In conclusion, this innovative technique provides a promising prospect for the treatment of heavy metal-organic complex wastewater, crucial for environmental protection and industrial sustainability.