Removal of tannins and polyhydroxy phenols by electro-chemical techniques

The removal of tannins and their basic molecules such as catechol, pyrogallol, phloroglucinol and resorcinol was studied by electro‐flotation and electro‐oxidation techniques. Iron rods and triple oxide (TaO2/RuO2/IrO2) coated titanium rods were used as electrodes for electro‐flotation and electro‐oxidation respectively. Interaction of tannins and polyhydroxy phenols with iron oxy‐hydroxide formed by anodic dissolution of iron was studied by UV‐Visible, FT‐IR and zeta‐potential measurements. GC–MS was used to identify the intermediate compounds formed during electro‐oxidation. Catechol, pyrogallol, phloroglucinol and resorcinol were found to be mineralized in the presence of triple oxide (TaO2/RuO2/IrO2) coated titanium electrodes. Catechol and pyrogallol were found to form insoluble organo‐metal complexes while resorcinol and phloroglucinol were found to adsorb on iron oxy‐hydroxide. The sludge thus formed was simultaneously separated from the aqueous phase by hydrogen bubbles. It was observed that the power consumption is relatively high for electro‐oxidation compared with electro‐flotation. The effects of pH and reaction time on their removal were also studied and the results are discussed. Copyright © 2005 Society of Chemical Industry