Electrocoagulation mechanism of perfluorooctanoate (PFOA) on a zinc anode: Influence of cathodes and anions

Abstract

Batch experiments were conducted to investigate the effects of cathode materials and anions (Cl−, SO42−, NO3−, and CO32−/HCO3−) on perfluorooctanoate (PFOA) removal in electrocoagulation process using zinc anode. The results indicated that the hydroxide flocs generated in-situ in the electrocoagulation process using the stainless steel rod as cathode were more effective than those using aluminum rod as cathode for the removal of PFOA after 20min of electrocoagulation at a current density of 0.5mAcm−2. Hydroxide flocs generated in-situ in the electrocoagulation in the presence of Cl−/NO3− could effectively remove PFOA from aqueous solution with the removal ratios of 99.7%/98.1% and 98.9%/97.3% using stainless steel rod and aluminum rod as cathode, respectively. However, the PFOA removal ratios were 96.2%/4.1% and 7.4%/4.6% using stainless steel rod and aluminum rod as cathode, respectively, in the presence of SO42− and CO32−/HCO3−. The different removal ratios of PFOA during the electrocoagulation process were primarily due to the fact that the hydroxide flocs generated in-situ were different in the presence of diverse cathodes and anions. We firstly demonstrated that Zn0.70Al0.30(OH)2(CO3)0.15·xH2O and ZnO generated in-situ in the electrocoagulation process (except for CO32−/HCO3−) using zinc anode and aluminum/stainless steel rod cathode governed the sorption of PFOA. The adsorbent hydroxide flocs in-situ generated in the presence of Cl− could effectively remove PFOA from aqueous solution containing CO32−/HCO3− anion at the initial hydroxide flocs concentration of 2000mgL−1. These results provided an effective and alternative method to remove PFOA from aqueous solution containing CO32−/HCO3− anion.