A thermodynamic analysis of the organic matter (chemical oxygen demand - COD) removal from synthetic oil-water emulsions by the electrocoagulation process was performed with the objective of determining the most stable ionic species under diverse pH and aluminum concentration conditions and identifying possible removal mechanisms. The analysis suggests that the predominant species during the reactive stage are the amorphous aluminum hydroxide (for the mononuclear speciation of aluminum) and the positively charged trimeric species, Al3(OH)45+ (for the polynuclear speciation of aluminum). The emulsion destabilization probably occurs by charge neutralization, carried out jointly by the polynuclear species and by positively charged aluminum hydroxide. This sorption mechanism is likely to be the primary coagulation mechanism during the reactive stage. The formation of aluminum hydroxide and/or oxide during the stabilization stage may also take place, which indicates the gradual change of the dominant removal mechanism to sweep flocculation.
Electrocoagulation; oil-water emulsions; organic matter (COD); thermodynamics
