Publication Details

Sivakumar, M. & Emamjomeh, M. (2005). Electrochemical method for fluoride removal: Measurement, Speciation and Mechanisms. Environmental Postgrad Conference; Environmental change: Making it Happen (pp. 1-8). Australia: School Civil & Chemical Engineering, RMIT.


Electrocoagulation/flotation (ECF) is a process of passing a steady electric current through a liquid to remove a known contaminant. When aluminium electrodes are used, the aluminium goes into solution at the anode and produces aqueous aluminium species and hydrogen gas is released at the cathode. The experimental results indicate that the pH of solution is an important factor in the removal of fluoride. The optimal pH was found to be between 6 and 7.5. When pHA l {O H )+2are predominant and aluminium hydroxide is tended soluble. However when pH>9, soluble species Al(OH)4 is found to be predominant species. The strong presence of the hydroxy-aluminium in the pH range of 6-7.5, maximizes the formation of fluorohydroxide aluminium complexes and it is considered to be the main reason for defluoridation by electrocoagulation. The residual fluoride in such solutions may occur in different dissolved forms (F‘, A1F2+, A1F4') or finely precipitated to solid forms such as Al(OH)3-xFx . The composition of the sludge produced was analysed using X-ray diffraction (XRD) spectroscopy. XRD analysis shows confirmation that the removal mechanism is a competitive ion adsorption between OH' and F' The dried sludge obtained by ECF shows the formation of Al(OH)3-xFx and provides confirmation for the main mechanism for fluoride removal.

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