DEPTH DISTRIBUTION AND CHEMICAL FORM OF IRON IN LOW CROSS-LINKED CRUD-REMOVING RESIN BEDS

Deep beds of low cross-linked ion-exchange resins have been tested as a means of corrosion-product removal from condensate water in boiling- water nuclear reactor (BWR) at Clinton Power Station, Illinois Power C ompany. The phase composition of iron deposits in two cores extracted at different times from the same used resin bed, and in particulate fi lters of influent and effluent water sampled prior to core extraction, were examined using Mossbauer spectroscopy. Deposits were predominant ly magnetite, hematite, goethite and lepidocrocite. Although the distr ibution of iron showed a pronounced maximum near the top 10-20 cm of t he bed with up to 15 mg Fe/cm(3), the percentage of different phases r emained constant along the entire core length. Only a minor fraction o f colloidal iron, consisting of ultrafine (similar to 3 nm) colloidal particles of amorphous ferric oxyhydroxide (ferrihydrite), was observe d. These findings are significant, because the iron trapped on resins is commonly believed to represent soluble Fe2+ species. Our results in dicate that the primary mechanism of iron removal is by mechanical fil tration of water-suspended particulates. Thus, the use of a deep bed c ondensate polisher as a filter produces an iron coating that inhibits cation exchanger performance; that particulate iron should be removed on a prefilter. (C) 1998 Elsevier Science B.V. All rights reserved.