Degradative hydrogen peroxide oxidation of chelates catalysed by metallophthalocyanines

Catalytic oxidation of various chelating agents in aqueous solutions, namely: diethylenetriaminepentakis(methylphosphonic acid) (DTPMP); diethylenediaminepentaacetic acid (DTPA); ethylenediamine tetraacetic acid (EDTA); nitrilotriacetic acid (NTA); and β-alaninediacetic acid (β-ADA) was studied. Hydrogen peroxide was used as oxidising agent in combination with five different metallotetrasulfophthalocyanines as catalysts. (Reaction temperature was set to 60 °C, which is expected to be the temperature of bleaching wastewaters of modern pulp mill in the near future. Among the uncomplexed chelating agents, EDTA was most readily degraded, while DTPMP and NTA were less degradable. β-ADA and DTPA concentrations remained high. The metal speciation of these chelating agents has a significant effect on their chemical degradability. Iron, manganese and sodium complexes were most degradable, while zinc, copper and calcium complexes were more difficult to oxidise.