Chelating agents are used to remove fouling deposits and surface films from industrial equipment. This paper discusses the mechanisms by which magnetite (Fe3O4) dissolves in chelating solvents. A general mechanism for the dissolution of scale is presented. The three reaction steps—reduction, proton, donation, and chelation—are considered in detail. The dissolution of Fe3O4 from a steel surface is summarized:
Data from a number of scale dissolution tests show that any of these steps may be rate controlling under specific conditions. A low concentration of a reducing agent or lack of a proton donor (such as H3O+ or NH4+) can greatly decrease the reaction rate. The stability constant of the iron chelate also affects the rate. EDTA is much more effective than NTA or citric acid.
Subject
Acids,
Iron oxide,
Corrosion rate,
Tubes,
Chelation,
Iron,
Dissolution,
Ammonium,
Acidity,
Constants,
Scale,
Magnetite,
Chemical reactions
National Association of Corrosion Engineers
1984
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