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DEGRADATION OF NITRILOTRIS (METHYLENEPHOSPHONIC ACID) AND RELATED (AMINO) PHOSPHONATE CHELATING AGENTS IN THE PRESENCE OF MANGANESE AND MOLECULAR OXYGEN. (R826376)
Citation:
Nowack, B. AND A. T. Stone. DEGRADATION OF NITRILOTRIS (METHYLENEPHOSPHONIC ACID) AND RELATED (AMINO) PHOSPHONATE CHELATING AGENTS IN THE PRESENCE OF MANGANESE AND MOLECULAR OXYGEN. (R826376). ENVIRONMENTAL SCIENCE & TECHNOLOGY. American Chemical Society, Washington, DC, 34:4759-4765, (2000).
Description:
Phosphonates are used in an increasing variety of industrial and household
applications including cooling waters systems, oil production, textile industry,
and detergents. Phosphonates are not biodegraded during wastewater treatment but
instead are removed by adsorption onto sludge. This study investigates the
degradation of phosphonates in the presence of MnII and molecular
oxygen. The half-life for the reaction of nitrilotris(methylene)phosphonic acid
(NTMP) in the presence of equimolar MnII and in equilibrium with 0.21
atm O2 is 10 min at pH 6.5, with the reaction occurring more slowly
under more alkaline or acidic pH values. The presence of other cations such as
CaII, ZnII, and CuII can considerably slow the
reaction by competing with MnII for NTMP. Catalytic MnII
is regenerated in cyclic fashion as the reaction takes place. Although
generation of a MnIII-containing intermediate appears likely,
electron transfer within the ternary complex O2-MnII-NTMP
cannot be completely ruled out. Formate ion, orthophosphate ion,
imino(dimethylene)phosphonic acid and N-formyl
imino(dimethylene)phosphonic acid breakdown products have been identified. This
work indicates that manganese-catalyzed thermal autoxidation of commercial
(amino)phosphonate chelating agents is likely to be an important degradation
mechanism in natural waters.