Tetrapolyphosphate‐Strengthened Electro–Fenton Process for Decomplexation of Zinc‐Containing Wastewater: Efficiency and Mechanism Study

This study investigates the enhanced electro–Fenton decomplexation of Zn‐EDTA using sodium tetrapolyphosphate (Na 6 O 13 P 4 ) as a supporting electrolyte. With an initial concentration of 100 mg·L −1 , a current density of 0.6 mA·cm −2 , H 2 O 2 dosage of 6 mL·L −1 ·h −1 , and Na 6 O 13 P 4 dosage of 2.0 mmol·L −1 , the decomplexation efficiency of Zn‐EDTA exceeded 80% after 60 min across a pH range of 3–7. Compared to the traditional Na 2 SO 4 system, Na 6 O 13 P 4 significantly improved decomplexation efficiency. Single‐factor experiments showed that lower pH, higher H 2 O 2 , and increased Na 6 O 13 P 4 enhanced the decomplexation efficiency of Zn‐EDTA. Mechanistically, the formation of complexes between Fe 3+ and tetrapolyphosphate effectively prevents the generation of iron sludge. This simultaneously maintains a high concentration of soluble iron species in the solution, thereby promoting an efficient Fe 2+ /Fe 3+ cycle and a sustained supply of Fe 2+ within the Na 6 O 13 P 4‐ based electro–Fenton system. Under the oxidative action of •OH and •O 2 − , Zn‐EDTA undergoes decomplexation and oxidative degradation. The intermediate products in the reaction solution are identified as fulvic acid‐like and humic acid‐like substances, with the final products predominantly comprising small‐molecular organic acids, ultimately achieving a mineralization rate of up to 71%. The findings provide theoretical insights and practical references for treating heavy metal‐complexed wastewater.