Metal Surface Decontamination Using 1-Hydroxyethane-1,1-Diphosphonic Acid

Substituted-ethane diphosphonic acids are an interesting moiety of organic acids because they display particularly favorable chemical characteristics toward the selective dissolution of metal oxides. In recent years, these systems have been studied to develop a cradle-to-grave process for the decontamination of ferrous metals typical of the nuclear power industry. This paper expands the understanding of this system to the dissolution of ferrous oxides found on corroded metals of nuclear facilities.It is found that pure iron oxides such as magnetite (Fe3O4) and hematite (Fe2O3) dissolved quickly (<1 h) using 0.5 M 1-hydroxyethane-1,1-diphosphonic acid (HEDPA) and a strong reducing agent; the oxides with slower kinetics are the spinel structures, such as the nickel ferrites (NiOFe2O3), which dissolved very slowly in the foregoing solution. These results were confirmed in bench-scale tests on actual carbon steel and radioactively contaminated stainless steel samples. The decontamination of actual stainless steel from a nuclear reactor vessel required high concentrations of both HEDPA and reducing agent. Methods for treating the spent HEDPA solution are discussed.