Effects of co-existing anions on fluoride removal in electrocoagulation (EC) process using aluminum electrodes

C. Y. Hu, S. L. Lo, W. H. Kuan

Research output: Contribution to journalArticlepeer-review

256 Citations (Scopus)


Batch experiments with bipolar aluminum electrodes and potentiodynamic polarization tests with monopolar systems were conducted to investigate the effects of the type and concentration of co-existing anions on defluoridation in electrocoagulation (EC) process. The results demonstrate that the type of the dominant anion directs the EC defluoridation reaction. The defluoridation efficiency was almost 100% and most of the fluoride removal reaction occurred on the surface of the anode in the solution without the co-existing anions, due to the electro-condensation effect. In the solutions with co-existing anions, most of the defluoridation took place in bulk solution. The residual fluoride concentration is a function of the total mass of Al(III) liberation from anodes and the types of the functions in the solutions with and without co-existing anions are different. The existence of sulfate ions inhibits the localized corrosion of aluminum electrodes, leading to lower defluoridation efficiency because of lower current efficiency. The presence of chloride or nitrate ions prevented the inhibition of sulfate ions, and the chloride ions were more efficient. Different corrosion types occurred in different anion-containing solutions and the form of corrosion affected the kinetic over-potential. The bypass flow causes the decrease of current efficiency and the proportion of the bypass flow of current increased due to a rise of the kinetic over potential and the conductivity of the solution.

Original languageEnglish
Pages (from-to)4513-4523
Number of pages11
JournalWater Research
Issue number18
Publication statusPublished - Nov 2003
Externally publishedYes


  • Aluminum
  • Bipolar electrodes
  • Co-existing anion
  • Corrosion
  • Defluoridation
  • Electrocoagulation (EC)
  • Fluoride
  • Potentiodynamic polarization test

ASJC Scopus subject areas

  • Water Science and Technology
  • Ecological Modelling
  • Pollution
  • Waste Management and Disposal
  • Environmental Engineering
  • Civil and Structural Engineering


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