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:

Fe3O4+Fe+8H++4 chelant→4 Fe(II)chelate+4H2O

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.

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National Association of Corrosion Engineers
1984
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