Depth distribution and chemical form of iron in low cross-linked crud-removing resin beds

Abstract

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 Company. The phase composition of iron deposits in two cores extracted at different times from the same used resin bed, and in particulate filters of influent and effluent water sampled prior to core extraction, were examined using Mössbauer spectroscopy. Deposits were predominantly magnetite, hematite, goethite and lepidocrocite. Although the distribution of iron showed a pronounced maximum near the top 10–20 cm of the bed with up to 15 mg Fe/cm 3, the percentage of different phases remained constant along the entire core length. Only a minor fraction of colloidal iron, consisting of ultrafine (∼3 nm) colloidal particles of amorphous ferric oxyhydroxide (ferrihydrite), was observed. These findings are significant, because the iron trapped on resins is commonly believed to represent soluble Fe 2+ species. Our results indicate that the primary mechanism of iron removal is by mechanical filtration of water-suspended particulates. Thus, the use of a deep bed condensate polisher as a filter produces an iron coating that inhibits cation exchanger performance; that particulate iron should be removed on a prefilter.