Electrooxidation of polyacrylamide in the wastewater from molybdenum ore flotation: Resurrecting molybdenite floatability and degradation mechanism

To enable the reuse of molybdenite flotation wastewater, it is necessary to degrade the residual flocculant polyacrylamide (PAM) to eliminate its inhibition on molybdenite floatability. This study adopted electrooxidation technology to degrade PAM and investigate its mechanism as well as its effect on restoring molybdenite flotation. Under optimized conditions (current density: 40 mA/cm², oxidation time: 60 min), the molybdenite recovery in the 10 ppm PAM system increased from 1 % to 96 %, with a total organic carbon (TOC) removal efficiency of 81.39 %. For the artificial mixed ore (molybdenite:quartz = 1:9), after treatment of the system containing 2.5 ppm PAM, the Mo recovery and grade increased from 17 %/10 % to 96 %/27 %, respectively. Characterizations via atomic force microscopy (AFM), contact angle measurement, and Zeta potential analysis confirmed that PAM forms a hydrophilic adsorption layer on the molybdenite surface via hydrogen bonding (evidenced by a contact angle decrease from 85° to 55°). In contrast, electrooxidation degraded PAM into short-chain fragments, reducing the PAM coverage on the molybdenite surface to 10.33 % and restoring the contact angle to 83°, thereby reconstructing hydrophobicity. The degradation pathway involves free radicals (·OH/·Cl/·ClO) attacking the PAM main chain to cause chain scission, generating small-molecule products containing alkenes and esters, which are ultimately mineralized into CO₂, H₂O, and NO₃⁻. This technology provides an efficient solution for flotation wastewater recycling and green mineral processing.