Electrochemically Assisted Coagulation of Wastes Polluted with Eriochrome Black T

The electrochemically assisted coagulation of wastes polluted with Eriochrome Black T (EBT; an azoic dye) is studied. The pH is the most significant parameter, and good removal efficiencies are only obtained for pH values under 6. The EBT removal percentages increase with the electrical current charge passed up to a given value and then they stabilize. The concentration of electrolyte does not seem to influence the removal efficiencies. However, electrocoagulations in sulfate media achieve better results than those carried out in chloride media. The operation mode (continuous or batch) does not affect the removal of EBT at high concentrations of aluminum dosed. For lower concentrations, the discontinuous process attains better removal of EBT for the same amount of aluminum electrogenerated. Two primary coagulation mechanisms can explain the experimental observations: the binding of aluminum hydroxo cations to EBT anionic sites at strongly acidic pH values, and the adsorption of EBT molecules on the surface of the positively charged aluminum hydroxide precipitate at close-to-neutral pH values.