Patent Number: 050358405
Section: summary

BACKGROUND OF THE INVENTION EDTA (ethylene diamine tetraacetic acid) is used as a chelating agent for cleaning scale from steam generators used for pressurized water reactors. These steam generators accumulate great quantities of precipitated iron oxides that reduce the heat transfer coefficient and the efficiency of the steam generator. Periodically, it is necessary to clean the precipitated material from these steam generators. A 10-15% ammonium EDTA salt solution is typically injected into the steam generator. Since EDTA is a powerful chelating agent, it coordinates the iron and solubilizes it. In nuclear power plants, the shell side or secondary side of these steam generators is supposed to be the "clean" side. However, minor leaks in the tubes may occur allowing material from the primary side to leak low levels of radioactivity to the "clean" side, primarily in the form of radioisotopes of cesium cobalt and other metals. Acidifying the metal salt containing EDTA chelating solution produces a metal salt contaminated H.sub.4 EDTA. The cost of stabilization, transportation and disposal of these wastes are high, making volume reduction of the metal salt containing H.sub.4 EDTA precipitate a cost-effective alternative. INFORMATION DISCLOSURE STATEMENT The reduction of the volume of radioactive waste products resulting from steam generator cleaning has been the subject of various U.S. patents. However, none of the patents discloses or anticipates a process for eliminating radioactive salts from an EDTA acid precipitate. U.S. Pat. No. 3,669,631 to Bellbrook, et al. discloses a process for removing radioactive materials from ion-exchange resins. The ion-exchange resins are used to remove radioactive metal isotopes from a cleaning solution. The radioactive isotopes are recovered by dissolving the ion-exchange resins in an acid/catalyst mixture and thereafter recovering the radioactive isotopes from the solution. U.S. Pat. No. 3,791,981 to Calmon discloses a method for reducing the volume of radioactive contaminated ion-exchange resins prior to their disposal. The method consists of contacting the ion-exchange resins with an organic solvent to physically reduce the ion-exchange resin volume. U.S. Pat. No. 4,704,235 to Arvesen discloses a steam generator descaling method that is accomplished in a single step in the absence of EDTA. U.S. Pat. No. 4,705,573 to Wood et al. discloses a descaling process that does not use EDTA. The process comprises contacting a scale-containing surface with a specific reagent. No mention of subsequent reagent purification is made. An article by Robert W. Hay et al. entitled Reactions of Co-ordinated Ligands. Hydrolysis of Tetramethyl Ethylene-diaminetetra-acetate and its Copper (II) Complexes discloses methods of producing Me.sub.4 EDTA from H.sub.4 EDTA. SUMMARY OF THE INVENTION A principal object of this invention is to provide a process for removing metal contained in an H.sub.4 EDTA complex. The process results in a significant reduction in the volume of the unwanted metal containing H.sub.4 EDTA complex prior to disposal. Accordingly, in a broad embodiment the present invention is a process for removing metal contained in a metal contaminated H.sub.4 EDTA. The metal containing H.sub.4 EDTA complex undergoes esterification in the presence of an esterification reagent to produce an esterification mixture comprising a metal salt and a liquid EDTA ester. The metal salt is then separated from the esterification mixture. In a preferred embodiment, the invention is a process for removing radioactive metal salts contained in an H.sub.4 EDTA precipitate. The radioactive metal salt is removed by esterifying a radioactive metal salt containing H.sub.4 EDTA with an esterification reagent, in the presence of an organic solvent, at esterification conditions including a temperature of from about 0.degree. C. up to about the boiling point of the esterification reagent but no greater than 220.degree. C. for a period of time ranging from 15 minutes to about 24 hours or more to provide an esterification mixture comprising a solid radioactive metal salt, excess organic solvent and a liquid esterified EDTA. The liquid esterified EDTA is then recovered from the mixture.